Guide to cleaning the fruit off palm seeds

Removing the fruit from palm seeds by the easiest, quickest and most cost effective method

The link to buy Juania australis seeds is here: Buy Juania australis seeds

The fruit would eventually rot away in soil, but the problem is that most palm seeds don’t stay viable for any length of time, it is therefore imperative that the fruit, which is often a germination inhibitor, is cleaned off the seeds in a fast and efficient way, so that the seeds can then be germinated as quickly as possible in the nursery.

In this guide we’re focussing on rare and valuable seeds (Juania australis and Pinanga tashiroi), for which care is required to not damage these very expensive seeds. You should note that seeds of many species of palm are incredibly tough and cannot be crushed even with a hammer, an example would be Acrocomia, Parajubaea or Butia ssp., and fruits of these can be easily placed in a bag then trampled under foot until the fruit comes away from the seed, well, the Acrocomia would need a bit more work than that! Nevertheless so many species don’t produce such indestructible seeds, and here we show you how to remove the fruit without damaging these more delicate seeds.

The first step is to try to harvest the seeds when they are fully ripe, picking only the ripe ones and leaving the rest. If you have time at hand, then placing a suspended sheet under the infructescence (bunch of fruit) and waiting for the ripe fruits to fall into the sheet would be the best method. But, in reality we seldom ever have the luxury of time and collection is usually done quickly. In this instance it is far better to cut the whole infructescence and allow the unripe fruits to finish ripenning while still on the infructescence.

Fig. 1. Pinanga tashiroi fruits

Fig. 1. Pinanga tashiroi infructescences, the yellow infructescence with the black fruits is fully ripe, the green infructescence with the red fruits is not yet ripe

The unripe Pinanga tashiroi infructescence (fig 1) was left together with the fully ripe one for 3 days in a warm room, during which time the ethylene gases produced from the fully ripe fruit goes to speed up the ripening process of the unripe fruit. At the same time the unripe fruit draws the remaining water and nutrition out of the green infructescence, had the red fruits been picked off separate then they would have dried out and not gained that remnant nutrition that they needed. All of these fruits went on to fully ripen and the germination test was 100%.

Fig. 2. Juania australis fruits

Fig. 2. Juania australis fruits.

Fig. 3. Scarified Juania australis fruit

Fig. 3. A scarified Juania australis fruit. A sharp knife is used to slice away some of the outer layers of skin and fruit to allow oxygen and water into the fruit.

Fruits of Juania australis (fig 2) have a waxy coating over the skin of the fruit impeding water penetration of the fruit. This also acts as a barrier to oxygen, and therefore slows the oxygenation and decomposition of the fruit by the natural enzymes (pectins) in the fruit. When fruit decomposes it is an effect of oxygenation of the natural enzymes in the fruit to digest it, so when it’s eaten, the animal extracts those nutrients of the fruit, or the fruit decomposes. The skin is the natural barrier to slow this process. We therefore need to damage that skin of the fruit, by bruising or cutting in a process called scarification. Juania australis is the most sought-after cool-tolerant palm species in the world and its seeds are therefore amongst the most expensive seeds in the world. We don’t just knock them about to try to damage the skin, we take great care to not damage the seeds contained. I’ve used a sharp knife to cut away slices of skin and fruit (fig 3) taking care not to cut too deeply and avoiding the seed contained. Once scarified the fruits are left in a warm room for several hours to oxygenate, this starts the decomposition process of the fruit.

The next step requires soaking the fruit in warm (not boiling) water. Some fruit has naturally high levels of pectin enzyme, and therefore decomposes faster. The Pinanga tashiroi seeds were cleaned of fruit within one day after scarification. This was easily done by rubbing the pre-soaked seeds between my hands, then rinsing the cleaned seeds in fresh water, and allowing to become touch-dry in the air. Juania australis fruits are naturally poor in pectin enzyme and therefore require several days soaking and fermenting to remove the fruit. I add additional pectin enzyme to the water, which you can usually buy in a wine-making shop as a white, crystalline powder. One tablespoon full will usually suffice. Normally, when soaking seeds to hydrate them before planting I would say that the water needs to be changed every day. This is because it stagnates (de-oxygenates) and drowns the emerging embryo in the seed. Seeds need oxygen for respiration during germination. Fermenting fruit is different, we don’t change the water, otherwise we would be throwing our pectin enzyme away and slowing the rate of decomposition. The seed, for the most part is protected from the water by the surrounding fruit, and as soon as the fruit falls away we remove, wash, and dry (to touch-dry) the seeds. The cleaned Juania australis seeds (fig 4) should never be allowed to fully dry out.

Fig. 4. Juania australis seeds

Fig. 4. Juania australis seeds, cleaned of fruit, not allowed to dry-out more than simply touch-dry, and they are now ready for germinating.

Current list of germinated palm seeds at Trebrown Nurseries

I’ve made a list of all the diferent species of palm seeds that we, at Trebrown Nurseries, have ever germinated, or attempted to try and germinate. There may be one or two species that I’ve missed off the list.

I’m not going to duplicate the list here. Rather to link directly to it: This is an archive list of all species of Palm tree ever germinated from palm seeds at Trebrown Nurseries.

The Native Palms of the Ryukyu Islands of Japan

Japan has six native species of palm tree. Four of these are endemic to Japan. There are a further three species, which have been cultivated in Japan for centuries. These are:
Rhapis excelsa (Thunb.) Henry, J. Arnold Arbor. 11: 153 (1930).
Rhapis humilis Blume, Rumphia 2: 54 (1839).
Trachycarpus fortunei var. wagnerianus Becc., Webbia 5: 70 (1921).

Two native species are found only in the Japanese Ogasawara-shoto or Bonin Islands (typical oceanic islands, located 1,000 km south of Tokyo, Japan). These are:
Clinostigma savoryanum (Rehder & E.H.Wilson) H.E.Moore & Fosberg, Gentes Herb. 8: 465 (1956). Endemic.
Livistona boninensis (Becc.) Nakai, J. Jap. Bot. 11: 222 (1935). Endemic.

The remaining four native species are the subject of this article, and these species are found in the Ryukyu archipelago of Japan or Nansei-shoto. These are:
Arenga ryukyuensis A.J.Hend., Taiwania 51: 298 (2006). Endemic.
Livistona chinensis var. subglobosa (Hassk.) Becc., Webbia 5: 16 (1920).
Nypa fruticans Wurmb, Verh. Batav. Genootsch. Kunsten 1: 349 (1779).
Satakentia liukiuensis (Hatus.) H.E.Moore, Principes 13: 5 (1969). Endemic.

The Ryukyu Islands (Figure 1) are a chain of Japanese islands that stretch south-west from Kyushu to Taiwan: the ÅŒsumi, Tokara, Amami, Okinawa, and Sakishima (Miyako and Yaeyama) islands, with Yonaguni the southernmost. The largest of the islands is Okinawa. These islands have a subtropical climate with mild winters and hot summers.

Ryukyu Islands

Arenga ryukyuensis
This palm is very similar to Arenga engleri from Taiwan, but differs in the pinnae being strongly ribbed adaxially, and the stems are only to about 2 m tall, whereas, Arenga engleri stems grow to over 4 m. tall. Arenga ryukyuensis seeds are also very globose, short and fat, whereas, Arenga engleri seeds are more elongate, also generally larger. Arenga engleri in Taiwan occurs at 200 – 1050 m. elevation, whereas, Arenga ryukyuensis is a lowland species, and occurs from sea-level up to about 300 m. Indeed, the more common localities to see A. ryukyuensis is on the coral limestone coastal rocks, often in the spray zone.

Arenga ryukyuensis and Cycas revoluta growing together in Okinawa, Japan.

Arenga ryukyuensis and Cycas revoluta growing together in Okinawa, Japan. © Phil Markey

A. ryukyuensis is usually seen growning together with Cycas revoluta, which is also very common, and can also be seen throughout the Ryukyu Islands growing on coastal rocks and cliffs.

Both the cycads and the palms are more frequent at lower levels, becoming more scarce at elevation, nevertheless, both are found at the highest elevations in Okinawa.

Right: Cycas revoluta Okinawa, Japan. Left: Arenga ryukyuensis and Cycas revoluta growing together in dense undergrowth, Okinawa, Japan.

Right: Cycas revoluta Okinawa, Japan. Left: Arenga ryukyuensis and Cycas revoluta growing together in dense undergrowth, Okinawa, Japan. © Phil Markey

Arenga ryukyuensis showing form, and white undersides of the leaves.

Arenga ryukyuensis showing form, and white undersides of the leaves. © Phil Markey

Another difference between Arenga ryukyuensis and Arenga engleri is the infructescence. A. ryukyuensis fruits are somewhat exposed and visible from above, growing out of the top of the plant. Whereas, A. engleri fruits are often hidden in amongst the leaves, and almost never visible from above. Fruit of A. engleri ripens from green, through an orange/yellow to dark purplish red. A. ryukyuensis ripens from green through yellow to orange then dark red.

Left: Arenga ryukyuensis fruits. Right Arenga engleri fruits.

Left: Arenga ryukyuensis fruits. Right Arenga engleri fruits. © Phil Markey

Taiwan is a new island that started being pushed up from the sea-bed around 6.5 Ma, by the north eastward movement of the Philippine plate crashing into the Chinese continental margin at 8 cm. per. year. This would have crashed through the Ryukyu archipelago / Luzon volcanic arc, pushing any pre-existing islands into the new Taiwan landmass. It is therefore logical to assume that Arenga existed first in the Ryukyu, which are very much older islands, and was then taken to Taiwan to evolve into Arenga engleri. It is not possible that there has been a land-bridge between Taiwan and the Ryukyu since that time.

Livistona chinensis var. subglobosa
I have written before about this species, so will not spend too much time discussing it here. Only to say that Livistona chinensis does not exist in its truly wild state anymore anywhere within the Ryukyu or Taiwan. In Japan, so-called virgin L. chinensis forest is now found only on the islets of Aoshima and Tsukishima in the Miyazaki prefecture, Kyushu, Japan. The islet of the gods on Aoshima is the extreme northern limit of the species, and this is also officially recognised as the largest single population of the species in Japan consisting of 4000 individuals. But as I have published before, this is not acurate, the largest virgin population of Livistona chinensis var. subglobosa is to be found on a tiny island called Uotsurijima (Japanese) or Diaoyudao (Chinese). This is the largest island of the Senkaku Islands (钓鱼岛及其附属岛屿) or what we know as the Pinnacle Islands. Uotsurijima or Diaoyudao Island located at 25°44’39”N 123°28’26”E has an area of 4.3 square kilometres (1.7 sq mi) and a highest elevation of 383 metres (1,260 ft). L. chinensis is the dominant tree species on this island and I estimate this population to be over 100,000 individuals.

Left: An interesting picture of Livistona chinensis var. subglobosa growing through an old house on Okinawa, Japan. Right: Livistona chinensis var. subglobosa in Taiwan tends to grow much straighter trunks.

Left: An interesting picture of Livistona chinensis var. subglobosa growing through an old house on Okinawa, Japan. Right: Livistona chinensis var. subglobosa in Taiwan tends to grow much straighter trunks. © Phil Markey

It is more often than not that the Japanese Livistona trunks are seen to be leaning, bent, twisted, and show irregular growth patterns. I’ve questioned this in Japan, and was told that the Ryukyu islands experience many typhoons, which bend the trees over. But, coastal Taiwan experiences the same typhoons, and the Taiwan trees tend to have much straighter, upright trunks. Another, difference is that many of the Ryukyu trees produce much more globose, almost round, seeds than do the Taiwan trees. The Taiwan Livistona produce more globose seeds than do the Chinese trees.

Nypa fruticans in habitat on Iriomote Jima, Ryukyu, Japan.

Nypa fruticans in habitat on Iriomote Jima, Ryukyu, Japan. © Phil Markey

Nypa fruticans
Nypa fruticans exists in Japan in one single, very isolated, and inaccessible population at Funaura on the island of Iriomote Jima.
This population of about 28 or more clumps are located a long way up a tidal tributary stream in a large mangrove swamp that surrounds a stunningly beautiful tidal estuary on the north of the island.

Tidal estuary and tidal tributary stream leading through the mangrove swamp. Iriomote Jima, Ryukyu, Japan.

Beautiful tidal estuary and tidal tributary stream leading through the mangrove swamp. Iriomote Jima, Ryukyu, Japan. © Phil Markey

The Nypa population is carfully monitored.

The Nypa population is carfully monitored. Some of the overhanging mangrove has been cleared away to see if this has any effect on the population growth. © Phil Markey

I must say that these Nypa palms are not good examples. Much better examples are to be seen, in much more accessible locations elsewhere in South-east Asia. The Japanese Nypa are located deep in an important mangrove, declared as a natural monument in 1959, well off the beaten track. This mangrove is an important habitat for wildlife, and is best left to the wildlife that inhabit it.

Nypa fruticans reproduces by vegetative propagation, each clump connected together under the mud.

Nypa fruticans reproduces by vegetative propagation, each clump connected together under the mud. © Phil Markey

The population is the world’s northernmost natural occurrence, and it has been rapidly reduced in size. Its genetic diversity examined by the Random Amplified Polymorphic DNA(RAPD) method showed that all 28 individuals examined were genetically identical and had no diversity. They are thus considered clones derived from a single individual by vegetative propagation. Because flowers fail to set fertile seeds, the species is likely to be self-incompatible. The population at Funaura is at an extinction crisis.

Nypa fruticans showing self-incompatible emergent flowers. Iriomote Jima, Ryukyu, Japan.

Nypa fruticans showing self-incompatible emergent flowers. Iriomote Jima, Ryukyu, Japan. © Phil Markey

Satakentia liukiuensis

Satakentia liukiuensis © Phil Markey

Satakentia liukiuensis
Satakentia contains only one species, which is endemic to Japan in the far south of the Ryukyu Islands in the islands of Ishigaki Jima and Iriomote Jima. This genus was named by Harold Moore for Toshihiko Satake, who had noticed it was something special. There is now a museum built to honour Toshihiko Satake within the main population of the palms on Ishigaki Jima.

Trunks can be very tall, brownish/grey, and solitary, topped with a prominent, brown or reddish green crownshaft, which is very distinguishable. With large green pinnate leaves, 3 m. long.
The inflorescences are also distictive, which are branched to two orders, and are borne below the crownshaft.

Trunks have a mass of adventitious roots at the base, and can grow to 20 m.tall. © Phil Markey

Trunks have a mass of adventitious roots at the base, and trunks can grow to 20 m.tall. © Phil Markey

Satakentia liukiuensis is in decline in its natural environment with no known cause, and it was once much more widespread throughout the two islands than it is today. However, plants are being raised in cultivation and are widely planted as a street tree in cities further north, notably Naha on Okinawa.

Satakentia liukiuensis in natural habitat. Ishigaki Jima, Ryukyu, Japan. © Phil Markey

Satakentia liukiuensis in natural habitat. Ishigaki Jima, Ryukyu, Japan. © Phil Markey

Satakentia is grouped in the subtribe Carpoxylinae, which comprises three genus – Carpoxylon, Satakentia, and Neoveitchia. Carpoxylon and Neoveitchia come from Vanuatu and Fiji, it is not clear how the natural distribution could extend to the Japanese Ryukyu for Satakentia.

Satakentia liukiuensis in natural habitat. Ishigaki Jima, Ryukyu, Japan. © Phil Markey

Satakentia liukiuensis in natural habitat. Ishigaki Jima, Ryukyu, Japan. © Phil Markey

Satakentia liukiuensis in natural habitat on Iriomote Jima.

Satakentia liukiuensis in natural habitat on Iriomote Jima. © Phil Markey

There are two main wild populations, the main population on Ishigaki Jima, and a much smaller population on Iriomote Jima with a few individual trees scattered across Iriomote. The Iriomote trees are inaccessible, as they grow in a cemetery, or the isolated trees are remote in the hills.

More info:
Satakentia liukiuensis trebrown.com
Nypa fruticans trebrown.com
Arenga ryukyuensis trebrown.com
Livistona chinensis var. subglobosa trebrown.com

The Natural Distribution of Livistona chinensis Past and Present

Including Livistona chinensis var. subglobosa and Livistona chinensis var. boninensis

There are three natural forms of Livistona chinensis formally known as Livistona chinensis (Jacq.) R.Br. ex Mart., Hist. Nat. Palm. 3: 240 (1838). from the Chinese mainland, Livistona chinensis var. subglobosa (Hassk.) Becc., Webbia 5: 16 (1920). from the Ryukyu archipelago of Japan & Taiwan, and Livistona chinensis var. boninensis Becc., Webbia 5: 12 (1921). from the Bonin Islands of Japan. However, these names have recently been taxonomically revised where Livistona chinensis var. subglobosa has been reduced to the species level as Livistona chinensis (Jacq.) R.Br. ex Mart., Hist. Nat. Palm. 3: 240 (1838). and Livistona chinensis var. boninensis is now Livistona boninensis (Becc.) Nakai, J. Jap. Bot. 11: 222 (1935).

Livistona chinensis var. subglobosa

Livistona chinensis var. subglobosa

Livistona chinensis var. subglobosa is perhaps justifiably not deserved of subspecies status, as the morphological differences are slight when compared with the Chinese mainland form. The main noticeable difference is to be seen in the size and shape of the seeds. The mainland China form, which is the commonest form in cultivation around the world produces a typically elongate, smaller seed (15 – 9 mm) than the Japan/Taiwan form which produces a larger, more globose seed (18 – 12 mm).

Livistona boninensis has had a much longer natural isolation, and differs in the height of the trunk being 18 m or more tall compared to 12 m for L. chinensis. Livistona boninensis‘ seeds are also larger but seldom ever as globose as L. chinensis var. subglobosa.

As I mentioned the mainland China form is by far the commonest form in cultivation with the main sources of seed being India, Pakistan, the USA and Europe. Livistona chinensis var. subglobosa from Taiwan and Japan is quite uncommon in cultivation outside of Taiwan and Japan, but is by far the most widespread and commonest form in the wild today. The former name of L. chinensis var. subglobosa was most useful as the indicator of provenance of the two main forms, and therefore identifying it as the Japan/Taiwan form and the most cold-hardy of the two (Zone 8b) (-6.7 to – 9.4). L. boninensis is equally as hardy.

Natural distribution of Livistona chinensis today

Livistona boninensis a palm native to Ogasawara-shoto or Bonin Islands (typical oceanic islands, located 1,000 km south of Tokyo, Japan), is endemic to several of the islands and introduced to the nearby Iwo (or Volcano) Islands. The Bonin Islands is a scattered archipelago of 20 or more rugged volcanic islands with many additional islets and rocks. The archipelago extends from the island of Mukojima in the north to the Iwo Islands in the south. The Bonins can be divided into three main clusters of islands: the Mukojima, Chichijima, and Hahajima-rettos groups. The native range of L. boninensis today is the Hahajima-retto group.
bonin-islands

The climate of the islands is subtropical, with a marked seasonal temperature variation, ranging from a sea level mean of 18°C in February to 25°C in July and August. A regular dry season occurs from January through March; sometimes there is also a secondary dry season in July and August.

The basal rocks of the Bonins were formed during the Tertiary 65 to 1.8 million years ago by submarine volcanic activity. Boninite, an andesitic volcanic rock rich in magnesium oxide, chromium, and silicon dioxide, is widespread, and is overlain in some areas by volcanic breccia. Most of the islands drop sharply to the ocean, with sea cliffs ranging from 50 to 100 meters in height.

The primary subtropical broad-leaved evergreen forest that remains on the islands can be classified into 3 major types. The palms occupy a dry forest on rocky slopes where the palm is a second dominant and is associated with Pandanus boninensis and Ochrosia nakaiana.

Livistona chinensis on the mainland of China no-longer has any truly natural wild stands of trees in any number. Small populations can still be found around Guangdong and on the island of Hainan. Although naturalised populations of the palm can be found in other areas of China and other South-East Asian countries, as well as some South Asian countries and Hawaii. The palm is commonly planted as a street ornamental throughout warm-temperate regions of the world.

Livistona chinensis var. subglobosa is naturally distributed from Taiwan through the islands of Okinawa and as far north as Kyushu, Japan, where it grows along shores washed by the warm Kuroshio current. However, due to it’s lowland habitat no wild populations exist in Taiwan today. In Japan, so called virgin L. chinensis forest is now found only on the islets of Aoshima and Tsukishima in the Miyazaki prefecture, Kyushu, Japan. The islet of the gods on Aoshima is the extreme northern limit of the species, and this is also officially recognised as the largest single population of the species in Japan consisting of 4000 individuals.

However, I report here, for the first time that by far the largest virgin population of Livistona chinensis var. subglobosa is to be found on a tiny island called Uotsurijima (Japanese) or Diaoyudao (Chinese). This is the largest island of the Senkaku Islands (钓鱼岛及其附属岛屿) or what we know as the Pinnacle Islands. Uotsurijima or Diaoyudao Island located at 25°44’39”N 123°28’26”E has an area of 4.3 square kilometres (1.7 sq mi) and a highest elevation of 383 metres (1,260 ft). L. chinensis is the dominant tree species on this island and I estimate this population to be over 100,000 individuals.

The Pinnacle Islands are a group of disputed, uninhabited islands currently controlled by Japan, but also claimed by both the Republic of China on Taiwan and the People’s Republic of China as part of Taiwan Province. The island group is made up of five small non-volcanic islands which sit on the edge of the continental shelf of mainland China, and are geologically separated from the Ryukyu Islands by the Okinawa Trough. Japan argues that these islets are part of the Ryukyu Islands. They are 170 kilometers (106 mi) north of Ishigaki Island, Japan; 186 km (116 mi) northeast of Keelung, Taiwan; and 410 km (255 mi) west of Okinawa Island.

The dispute appears to date from the 1968 announcement by two Japanese scientists that there may be large reservoirs of oil under the continental shelf below the islands. From the end of World War II until 1972, the United States occupied Okinawa, and controlled the islands, whose ownership was undisputed until 1970, when both China and Taiwan began to claim that the disputed islands were given to Japan in the Treaty of Shimonoseki in 1895 and should therefore be returned to Taiwan (after the end of World War II in 1945, all “unequal treaties” forced on China were declared void, including the Treaty of Shimonoseki, concluded in 1895). In 1971, the US expressed its intention to hand over the occupied territories, including the disputed islands, to Japan. Both the China and Taiwan governments protested and reiterated their claim to sovereignty over the islands. Taiwan made the official announcement on 11 June 1971, followed by China on 30 December. However, the United States handed over the disputed islands to Japan in 1972, even though they have not taken a definitive position on the sovereignty of the territory, considering the islands an “administrative territory” of Japan.

After losing the First Sino-Japanese War, Qing China signed the Treaty of Shimonoseki on 17 April 1895. This Unequal Treaty ceded Taiwan, Okinawa and its surrounding islands to Japan. The Chinese governments see the disputed islands as having been included in the islands ceded to Japan by the treaty, even though the Treaty did not explicitly enumerate all the islands ceded under it. On this basis, they argue for Chinese sovereignty over the islands for two reasons. First, that all the Unequal Treaties are null and void and thus the islands are still part of Taiwan Province of China. Secondly, that since the disputed islands were ceded along with Taiwan in 1895, therefore when Japan returned to China all territories it had obtained from China since the First Sino-Japanese War at the end of World War II, the disputed islands were returned along with Taiwan to China.

The first frustrating issue regarding this dispute is that no scientist can get anywhere near the island to evaluate the palm population or any of the other flora & forna. The Senkaku mole (Nesoscaptor uchidai) is an endemic mammal to the island and could, for all we know be extinct now. The second frustrating issue is regarding the feral goat population on the island, which is totally out of control. A sum total of 3 domestic goats were deliberately introduced to the island in 1978. There is now an estimated 300+ animals devastating the juvenile palm population, and due to the dispute over the island no government is prepared to send in hunters to eradicate the goats.

Distribution map for Livistona chinensis

Distribution map for Livistona chinensis

Natural distribution of Livistona chinensis in the past

The historical distribution of Livistona chinensis was certainly much more widespread than it is today. It is known to have occurred on Tsushima island (at latitude 34°N) located to the south of the Korean Peninsula. Evidence also points to the species being much more numerous on all the islands it occurs on today.

When haplotypes from the amplified DNA band patterns of the Japanese distribution of the species were compared by Japanese scientists they concluded the true origin of the species points to northern Taiwan, Iriomotejima, Ishigakijima and Okinawa in Japan. These same scientists also supported the hypothesis that natural distribution throughout its range in the islands occurred through oceanic drift of seeds on the Kuroshio current. I totally disregard this hypothesis based on the facts that viable seeds do not float even on salt-water, and that salt-water quickly kills the developing embryo within the seed.

Therefore, we need to look for lower sea-levels during the ice ages to see how distribution of this palm occurred. The current interglacial that we are currently enjoying started about 12,000 – 10,000 years ago when the planet warmed and the ice-caps started to melt making the sea-level rise. That last glaciation lasted roughly 100,000 years, where the Glacial Maximum occurred about 20,000 – 18,000 years ago, and it was at this time that the sea level was at its lowest, roughly 120-150 m lower than it is today.

China - Japan sea-levels during last Glacial Maximum

China - Japan sea-levels during last Glacial Maximum

As you can see from the map the lower sea-level explains how Livistona chinensis extended from Taiwan to Japan and Korea in the north, and to Hainan China in the south. However, this does not explain how the palm spread throughout the islands of the Ryukyu Archipelago of Japan. Nor does it explain how Livistona boninensis reached the Bonin Islands of Japan. For the palm to be able to reach, and spread through the Ryukyu from Taiwan the sea-level would have needed to be at least 400 m lower than today. To reach the Bonin Islands would have required a sea-level at least 1500 m lower than today. If we go back even further in time to evaluate even earlier Ice Ages then the Ice Age preceding the last occurred about 145 million years ago between the Jurassic and Cretaceous. But this Ice Age was not as cold, and did not produce very low sea-levels. Besides, we have not been able to find any palm relatives in the fossil record which date older than about 115 – 120 million years.

We have already mentioned that the Bonin Islands were formed during the Tertiary 65 to 1.8 million years ago by submarine volcanic activity. This same is true for the entire Philippine Arc of volcanic islands, which includes the Batan Islands of the Philippines and the Ryukyu Archipelago. The island of Taiwan is even younger and was formed less than 6.5 million years ago by the Luzon Volcanic Arc crashing into the Chinese continental margin and in doing so forced the land mass of Taiwan up from the sea bed.

The Pacific Rim, of which the Ryukyu is part was much hotter and far more active in the past, and during the last 1.8 million years has been rapidly cooling. With this the Ryukyu Archipelago and the Bonin Islands of Ogasawara-shoto have been sinking in a process called Ridge Subduction. Newly created, hot rocks are buoyant on the mantle, and therefore rise, displacing the seawater above it. Thus making shallow seas. As the rocks cool over time they sink further into the mantle. Making deep water above them. The full extent of the elevation they once were and the amount they have sunk is too difficult to quantify. But 1000 – 2000 m is not impossible, and this could be the answer we are looking for. Failing this the only explanation could be that seeds have been carried there by humans or birds, or that the seeds got there by floating on oceanic debris.

Conclusion: Livistona chinensis possibly occurred in the northern Taiwan area around 1.8 to 20 mya., but could have arrived there as late as 20,000 – 90,000 years ago. The species reached its maximum around 20,000 years ago when the sea-levels were 120 m lower than they are today. During this time its distribution stretched from southern China to Korea and as far north-east as Tokyo Japan. We assume that the islands of Ogasawara-shoto and Ryukyu Archipelago were much higher than they are today, and that 20,000 years ago they were still high enough to form a land bridge. Livistona boninensis became isolated at a very early stage, and Livistona chinensis has been slowly declining in numbers in recent times.

The world’s rarest wild palm tree Corypha taliera is dying

The last wild Corypha taliera has started to flower and will now die

Corypha taliera is a solitary, massive, moderately slow growing, monoecious palm with a hapaxanthic or monocarpic mode of growth where the plant dies after setting seed. The palm grows for say 80 years without producing a flower, then upon coming of age the flower grows out of the top of the tree, the leaves die and fall off leaving a massive terminal panicle flower atop the massive trunk. C. taliera holds two world records which it shares with Corypha umbraculifera, the largest flower structure among flowering plants and the largest palmate leaf which is 6 m. (20 ft.) wide.

Corypha taliera

Corypha taliera

Although the palm in the scrub jungle on the Dhaka University campus is the last known Corypha taliera growing in the wild, the International Union for Conservation of Nature and Natural Resources (IUCN) has already classified the plant on its Red List, as being “extinct in the wild”. This is because molecular work – which is required to confirm the identification – still hasn’t been taken out on the plant. Until molecular work is carried out, they will only say that this plant has been “tentatively identified”. Also, IUCN say that it’s unclear about whether or not the specimen originated from cultivated material. They also mention that the plant is effectively in a “cultivated state”, and therefore probably wouldn’t count towards the “wild” classification. Although not in the wild, Corypha taliera specimens are currently growing in the Indian Botanic Garden and the Fairchild Tropical Garden in Florida, USA. Because these aren’t growing in the natural environment, they don’t count for “wild” plants hence the IUCN classification “Extinct in the Wild”.

No other specimen of Corypha taliera palm has been found in the wild in almost 30 years. In 1979, a C. taliera, located in the Birbhum district of West Bengal in a village near Shantiniketan, had begun flowering. The locals fearing that it was a “ghost palmyra palm” Borassus flabellifer, due to its horn-like flowers, chopped it down before the flower could set seed.

But all is not lost. This news that it is dying is good news

This is not the last Corypha taliera palm tree in existence, it is merely the last in a wild state. There are several trees still remaining at the Adward Park, Bogra, Bangladesh, and also Howrah botanic garden in India. A cultivated specimen in Howrah botanic garden ultimately flowered and its seeds were saved and raised to seedlings with some sent to the Fairchild Tropical Garden, Florida, USA. These plants are now quite large and will flower in about 80 years.

Our tree at the Dhaka University campus will ultimately produce millions of golf-ball sized seeds, which will rain down for months. These seeds will be raised into new trees. We now have good hopes of increasing the population and re-planting back into the wild. Talks are undergoing, but it currently looks like none of these seeds will be distributed abroad, and all will be planted in its native land.

Does nicking seeds speed up germination?

This was originally submitted as a question on our old Trebrown forum.

“I was wondering if nicking seeds helps speed up germination on bananas and palms, specifically Jelly Palm seeds? What I mean by nicking is that you cut, scrape or grind away a small piece of the outer seed shell/husk so moisture can quickly enter the seed. I do this on some of my tropical water lilies and lotus and it works great. Thanks, Mike.”

The process is called scarification, where the outer seed coat is scratched to better improve water permeation to reach the Endosperm (seed). It can be done, and many people will swear by it as speeding up germination. We here germinate hundreds of thousands of seeds every year and we NEVER do this. If you attempt this you must be very careful not to go too far and break through and damage the seed. This is the best way to rot your seeds. Of-course the seed needs water to germinate, and many hard coated seeds, if they are very dry or oily will reduce that flow of water. I know from experience that the best way to hydrate seeds is to soak them for longer. Up to a couple of weeks if necessary, but usually 3 days will suffice. Warm to hot water is better. However, make sure you change the water daily or you’ll deplete the required oxygen from reaching the seed, and fungus could also attack the seed. Seeds have hard seed coats to protect the seeds. It’s natural, and seeds will germinate with their coats on. Perhaps one exception could be used if you are persistently trying to germinate as many Jubaea chilensis or Butia species as you possibly can. This process cannot be used for all Butia species, just the fatter seeds. That is, if you’ve tried to germinate a batch of seeds and there are a few remnants after trying for a whole year, then you can try completely removing the whole shell. To do this you would need to crack open the shell in a vice and carefully remove the soft seed without damaging it. It will be obvious to you if the seed is still good or not. The good seeds must then be dipped in a fungicide and germinated in sterile conditions. These will either germinate within a month or die. So always leave this method as the last option. There are many methods used for germinating different kinds of seeds. The oily seed requirement is an important one, which requires frequent washing and leaving seeds in the sunshine to heat-up and dissipate the oil, a process developed for pre-treating Oil palm seeds (Elaeis). There are too many methods for me to list in this thread. I’ll leave those for specific species questions. But I will answer your questions here Mike. Bananas – always soak for a few days. Adding a teaspoon full of potassium nitrate to the water will soften the shell. Always plant the seeds in a regular seed mix. Don’t try the baggie method. 30°C. Keep the soil moist, and the plants humid. Jelly Palm – Butia capitata (I mentioned it above) Soak the seeds for up to 2 weeks if necessary. Adding a teaspoon full of potassium nitrate to the water will soften the shell. Germinate in sealed plastic boxes in a simple medium like Perlite, Vermiculite, Coir or Peat, where the seeds lie on the surface or half buried in the medium. There must be an inch of air space at the top of the tub. And the temperature must fluctuate between about 5°C – 35°C (40°F – 100°F). Seeds will take a month or 2 to start germinating. The ungerminated seeds can then be soaked again, and tried again.

“Thank you Phil for the quick reply. Wow that was a great explanation. It made a lot of sense. I was already soaking the Jelly Palms but will continue for another week with regular water changes. Where do you get potassium nitrate from? Mike.”

Potassium nitrate is the saltpetre, or saltpeter (American spelling) used in gunpowder manufacture. Chemical formula KNO3. I don’t know where you are in the world Mike, but you can no longer buy this off the chemist’s shelves here in the UK. It used to be easy to get, but I guess these days they’ve found alternative remedies for the ailments it was used to treat, and it’s a banned product for obvious reasons. Ironically, those who want to buy it to make explosives can still do so in the large quantities they need direct from the wholesale suppliers in the USA. That is your problem! You would need to buy it in massive quantities, which is not practical for the average seed grower. It really isn’t necessary to use this though. Just soak your seeds for longer if necessary. Seeds from Butia, Jubaea and the rest of that family respond well to temperature fluctuations. Whenever, you need to re-soak your remnant seeds try putting them in a glass jar of water and leave it in the hot sun in a glasshouse all day. That method of soaking really makes them jump.

“Well all this info came at the perfect time. I have Butia x Jubaea seed that arrived today. Cheers, Las Palmas Norte.”

Paschalococos disperta The Extinct Palm from Easter Island

Moai Statues on Easter Island

Moai Statues on Easter Island

Easter Island (Rapa Nui) is one of the world’s most isolated inhabited islands. It is 3,600 km (2,237 mi) west of continental Chile and 2,075 km (1,290 mi) east of Pitcairn in the South Pacific Ocean, and is a volcanic island, consisting mainly of three extinct volcanoes. Easter Island is famous for its monumental statues, called moai, created by the Rapanui people. The Dutch explorer Jacob Roggeveen named the island Easter Island when he encountered it on Easter Sunday 1722. At that time he visited for a week and estimated there were 2,000 to 3,000 inhabitants on the island, and noted a seashore lined with stone statues. When British explorer James Cook visited Easter Island in 1774, he reported a reduced population, and the statues as being neglected with some having fallen down. Easter Island was approached many times during the 19th century, but by now the islanders had become openly hostile towards any attempt to land, and very little new information was reported before the 1860s. A series of devastating events killed or removed almost the entire population of Easter Island in the 1860s. In 1877 there were just 111 people living on Easter Island, and only 36 of them had any offspring.

Paleobotanical studies of fossil pollen and tree moulds left by lava flows indicate that the island was formerly forested, with a range of trees, shrubs, ferns, and grasses. The original subtropical moist broadleaf forests are now gone. A large palm, Paschalococos disperta, related to the Chilean wine palm (Jubaea chilensis), was one of the dominant trees. This palm is now extinct. Introduced trees are now sparse on Easter Island, rarely forming small groves. The island once had a forest of palms, and it has been argued that native Easter Islanders deforested the island in the process of erecting their statues. The disappearance of the island’s trees seems to coincide with a decline of its civilisation around the 17th and 18th century. Only a quarter of the statues were installed, while nearly half still remain in the quarry at Rano Raraku and the rest elsewhere on the island, probably on their way to final locations. Legend says that the statues walked to their final resting places around the island, but probability states that it would have taken 50 men and heavy rollers to move the statues, the largest of which weighing 82 tons. These rollers would have had to be very large and points to them being of the size of Jubaea chilensis sized trunks 4-6 ft in diameter.

Easter Island palm tree glyphs

Easter Island palm tree glyphs

Paschalococos disperta was almost certainly indistinct from Jubaea chilensis. All evidence; heavy trunks 80 ft tall, pollen from lake beds, hollow endocarps (nuts) found in a cave, and casts of root bosses all being identical to those of Jubaea chilensis. We even have glyphs carved into wooden tablets which distinctly depict the unique Jubaea chilensis palm tree shape.

If we take a look at the life-cycle of Jubaea chilensis then the reason for the human demise becomes much more apparent. Jubaea chilensis produces a massive, columnar, smooth trunk. The trunk has a wide girth (4-6 ft) for approximately 50 years of its growth. During this first 50 years the tree is not yet of reproductive age and does not produce fruits. After 50 years of growth the trunk then narrows down to less than half of its previous girth forming the typical wine bottle shape. It is only then that the tree starts to reproduce. Therefore, if you assume that the people cut down the larger trees first then they have systematically stopped all reproduction of the species until younger trees reach fruiting age. The people would have lost an important food source in the nutritious nuts, and there would be no new seedlings. We then assume that the people in their demand for rollers and dugout canoes would have cut down the next largest of the palm trees. Therefore, delaying reproduction of the trees yet further. If they were only left with young trees then waiting 50 years for reproduction would have been unrealistic and any trees that were left would have been cut for rollers without hesitation. Assuming they looked upon the moai statues to bring them prosperity then as hardship for the islanders worsened they would have increased production of statues, using up more and more rollers until they were all gone. And with no more wood to build boats for fishing the people died out.

The overall picture for Easter Island is the most extreme example of forest destruction in the Pacific, and among the most extreme in the world: the whole forest gone, and all of its tree species extinct.

Palm Seed Storage Behaviour

A comprehensive guide to storing and germinating palm seeds

If you have read any article about germinating palm seeds then the general advise would have been that the fresher the seeds are, the better the results will be. This, on the most part is very good advice and is a good method to work to. However, you will undoubtedly find that you do not achieve 100% germination of your seeds. Some species will germinate better than others, but some species will repeatedly produce poor results for reasons possibly relating to the environmental conditions that you are germinating them in. However, you should consider the fact that a palm tree may produce a large quantity of non-viable seeds within any bunch, and some seeds within a bunch at the time of harvest may not be fully matured enough. Also some seeds amongst the bunch may have a parasitic insect infestation which is not visible to the outside of the seed. Damaged seeds can often be removed as floaters during the initial seed cleaning process by the collector and this is usually the case, as the collector tries to ensure the quality of the seeds he is supplying. (Note: not all palm seeds sink in water).

Consider this simple experiment:

Take 2 random samples of 100 seeds from a fresh batch of seeds. One sample is planted immediately in your preferred method for germinating palm seeds (the method that works best for you). The second sample is soaked over night in water and then allowed to become touch dry before placing in a sealed plastic bag for cool room storage. If the bag quickly mists up on the inside under normal room temperature then the seeds were not dried enough. Remove the seeds from the bag and dry some more before re-bagging. These, now soaked, then dried, then bagged seeds are now stored in a slightly cool room out of direct sunlight for a period of 3 months. After the elapse of 3 months, remove the seeds and soak overnight once again. The next day discard any seeds that are floating on the water, and discard any seeds that are obviously not looking good. You must now count exactly how many seeds out of your 100 you now have left. Now plant the second batch of seeds using the same method as the first batch. After a considerable time (perhaps one year) has elapsed, and you now have all the visible seedlings you are likely to get from the two batches you should now count how many you have in each batch. The results, if everything was done correctly will show about the same number of seedlings in each batch, though the germination percentage will be much higher in the second batch per number of seeds planted. For this reason germination percentages mean absolutely nothing at all without recognised benchmarks by which to calculate. A reputable seed supplier will know the expected shelf-life of his seeds, and will have made every effort to keep the germination percentage per seeds supplied to the optimum. Which explains why you often get higher germination percentages from older seed supplied.

Obviously this is an example and few species of palm have similar optimum seed storage requirements. But from a growers perspective a simple way of guessing is to consider the natural environment of the species. A species from a tropical jungle will have seeds that generally have a very short shelf-life, there will be losses if the seeds are fresh or if they are stored. If stored the seeds will become much more difficult to germinate and the losses will be higher, most tropical, low elevation palms’ seeds will lose viability if stored at temperatures below 15°C (60°F). If it is a species from arid deserts then a preliminary storage together with regular testing will usually produce a higher germination rate of supplied seed. Other considerations are that if the species comes from high altitude then they usually have a naturally low seed water content and these seeds can usually be stored under cool conditions for periods of time.

The traditional method for testing if a seed is good is to slice it in half and take a look at the embryo. If the embryo is malformed, discoloured, or smells bad then it is unlikely to germinate. But if it looks good then it is still not going to grow because you’ve just cut it open, and even good looking seeds (if not cut open) can still be inviable. Obviously many species are rare, and the few seeds which may be available can be expensive. Cutting open seeds to look at and sniff is not a good idea. Besides, many palm species produce what is known as a ruminate seed, where the seed coat is enfolded, creating dark, tangled streaks in the endosperm. Ruminate seeds cannot be inspected very easily. For these we can however use the Tetrazolium Chloride test to give us a much more accurate and quicker result. The method is to Mix a 1% (10 gm/l) aqueous solution of tetrazolium chloride. Cut a sample of the seeds in half to expose the embryo and place the half containing the embryo in the solution. Put the container in the dark for 2-24 hours. On inspection, if the embryo stains partially or completely red or pink, it is probably viable. If there is no stain, the seed is likely inviable.

It is a good idea to test sample seed lots for viability before purchasing large quantities. If the Tetrazolium Chloride test is beyond you try using the seed float test. The seeds are placed in water for 24 hours and those that float are discarded as inviable. However, some palm seeds naturally float because they are dispersed in nature by water. Furthermore, some growers have found that if the floating seeds are planted, a sizable number will in-fact germinate.

For some species of palm namely Butia and Jubaea it appears that 3 months warm dry storage of seeds is required prior to planting. More research is needed to identify why this is. However, it may be that the embryo requires a period of time to fully mature. We know this to be true for many Cycad species. Cycad seeds must be dry stored for a period of 3-12 months before planting, whereas fresh seeds can quickly rot when planted. The seeds of the Cycad genus: Macrozamia can be stored for six years and still produce 100% germination.

With few exceptions palm seed should be collected when the fruit is completely ripe (showing full colour), or as soon as it falls from the tree. A few exceptions have been noted. Seed from green fruits of queen palm Syagrus romanzoffiana germinate better than seed from half-ripe or ripe seed, perhaps due to inhibitors in the fruit.

For seed banking purposes palm tree seeds are generally considered to be ‘non-orthodox’ Most plant species have seeds that stay viable when dried to the low moisture contents necessary for long-term storage. These are termed ‘orthodox’ species. Palms fit into the categories of recalcitrant and intermediate species, where a medium to high water content must remain in the seed, and seed cannot be conserved long-term in a seed bank via pre-drying and freezing.

The water content of the developing seed is similar to that of any actively growing tissue – about 70 to 80 percent. As the seed reaches maturity and the stage at which it is shed from the plant, its moisture content drops rapidly. The amount of water that remains at maturity depends on the species of the plant and the environment in which the seed matures. The seeds from tropical rain forest palms generally contain over 50% moisture, whereas palm species’ seeds from arid environments can have very low, almost orthodox levels of water content. Similarly, palm species which grow at high elevation have seeds which contain around 18% less moisture than related species at low elevation. This lower water-holding capacity of seeds from higher elevations suggests that plant tissues that must survive severe cold usually contain less water than those of warmer climates. The mechanism by which the living seed is protected under such varying conditions of development can be related to their chemical composition.

When water and heat are applied to a seed the embryo within the seed draws on its endosperm for the nutrients it needs to germinate and grow. A delicate balance of internal conditions regulates its life processes. The living seed is able to incorporate small molecules and simple substances such as glucose, phosphorus, and sulphur into complex chemical units of a cell. These organised parts are the cell wall and the protoplasm, which contains the cell nucleus. Enzymes act as the go-between in these conversions and building processes. The energy for this work comes from the breakdown, or catabolism, of some of the cell’s chemical components, usually by combining them with oxygen in the process called respiration. Most of the seed components from which the enzymes of the protoplasm and cell walls form new cells can be classed as proteins, fats, carbohydrates, organic acids, and amino acids. Thus the seed lives as long as its outside and internal environments maintain active enzymes and a good balance of chemical substances. Only under these conditions can the embryo, the result of the fusion of the sperm and egg nuclei, produce new cells and a healthy plant.

Moisture, temperature, and gases, particularly carbon dioxide and oxygen, can affect markedly the enzymes and chemical components of the living seed. Fungi, insects, bacteria, chemicals, or light can diminish or destroy the seed’s power to germinate. Many of the same factors, in the right concentration or combination, can enhance the life processes of the seed. Although enzymes are present in dry seed, they are activated only on movement of water into the seed. As the temperature increases, the rate of metabolism enzyme activity also increases. One measurable product of this metabolism is the amount of carbon dioxide given off and oxygen taken up. A rapidly metabolising seed has a higher gas exchange rate than a quiescent seed. If the energy made available by respiration is not used in growth, it is liberated as heat, and the temperature of the stored seed goes up. Water content, one of the most important factors in seed viability, therefore cannot be considered alone. If the water content within a seed is too high, large amounts of the chemicals required for growth will be used up. The seeds will then be unable to germinate when they are placed under proper conditions. Removal of too much water from the seed also causes death.

Changes in organic compounds also occur with the uptake of oxygen and release of carbon dioxide in living, but non-growing, seeds. If these seeds are germinated, the rate of respiration increases, and the chemical changes, uptake of oxygen, and release of carbon dioxide are easy to detect. The gas atmosphere surrounding mature seeds can determine if the seeds remain alive. If a container of seeds is evacuated and the oxygen pressure reduced, the seeds keep better than in air. Lack of oxygen retards respiration. Palm seeds planted too deeply in the soil, where little oxygen is present, will not live. As the depth of planting increases, the available oxygen and seed survival decrease. Wet or poorly drained soils also lack oxygen and inhibit the living processes of the seed. Ravenea musicalis is remarkable in being the only truly aquatic palm species. It grows in a single fast flowing river in Madagascar. It’s seeds germinate while still on the parent tree and then drop into the water, sink to the bottom, and commence growth under water. Most seeds immersed in water for lengths of time will die unless air is bubbled through the water. Also a shortage of oxygen usually kills a seed when the temperature or respiration is high. This happens because enzymes need oxygen to produce energy for growth of the embryo. The energy is released when the enzymes combine oxygen with various cell compounds. Good air circulation is therefore an essential ingredient for germination of palm seeds under their high temperature environmental requirements and is one of the primary reasons why seed soaked in stagnant water, or seed germinated using the polly-bag (Baggie) method so often fail. Direct sowing of palm seed into deep pots of a well drained soil produces a much better yield and a much safer option to the polly-bag method of germination.
Sometimes, however, high levels of oxygen are not required by the living cell to obtain energy from its chemical compounds. Some seeds have an abundance of the anaerobic enzymes, which function without oxygen. These enzymes produce enough energy for certain life processes. The Nypa fruticans palm is an unusual and primitive example that grows in tidal mud banks, in mangroves and even in salt water in tropical Asia. Its seeds do not require much oxygen to function. The cells of the embryo and seedling have a system of anaerobic enzymes and a special kind of respiration that requires little oxygen. Its seeds can remain viable and germinate under water which contains too little oxygen for the survival of most seeds.

Carbon dioxide, the end product of respiration, also has marked effects on seed viability. If it accumulates inside the seed or in the soil environment surrounding the seed, injury may result. The role of carbon dioxide is difficult to study, because gas concentrations inside and outside the seed may differ widely and the effects vary with the temperature. Accumulation of an enzyme product, such as carbon dioxide, in the living cell slows down the enzyme that produces the product. When seeds are stored for a long time, factors that increase the carbon dioxide around them frequently must be controlled to assure maximum viability. Fungi and bacteria can produce large amounts of carbon dioxide. These micro-organisms commonly occur on and in seeds. They, too, require water to grow, and drying the seed to low moisture inhibits their activity. Bacteria and fungi also contain enzymes, which metabolise and convert chemical compounds. They usually affect the chemicals on the seedcoat or in the seed. Some fungi or bacteria produce chemicals that harm the embryo. Some may produce compounds or excrete enzymes that soften the seed-coat, so that air and water diffuse into the seed and hasten its metabolism and loss of viability. Others may metabolise and exhaust the seed’s storage compounds. Old seeds and seeds that are stored under unsuitable conditions of moisture and temperature are particularly susceptible to attack by micro-organisms, usually to the detriment of the seed. The seedcoat therefore often is treated with a chemical disinfectant before it is stored.

Old seeds, which show marked decreases in nonsoluble carbohydrate or protein, germinate poorly. The breakdown or coagulation of protein in old seeds may advance so far as to modify the protein present in the nucleus. When that occurs, the seeds usually die. If such seeds do germinate, they frequently produce mutant plants. Some success has been achieved by attempting to replenish the carbohydrate or protein food source for the embryo by soaking the seed in seaweed extract fertiliser prior to sowing. Preliminary studies on ancient lotus seeds report the presence of an enzyme called L-isoaspartyl methyltransferase which may play a role in anti-ageing through their repair of proteins. Research such as this may one day provide a rejuvenation product for use with old palm seed.

Inhibitors, including many compounds that occur naturally in living seeds, keep the seeds dormant until conditions are favourable for germination. Some seeds contain compounds that enforce dormancy until there is enough water in the soil to leach the inhibitors out of the seed. The concentration of such inhibitors diffusing out of seeds or roots may be great enough to prevent germination if seeds are sown too close together or too close to other plants. But these same inhibitors, reduced to sufficiently low concentration, may stimulate germination. Many of these inhibitors are lactones; parasorbic acid and coumarin are two examples. They apparently prevent germination by inactivating certain enzymes necessary for elongation of the radicle. Palm seed sown in a well drained soil soon degrades any inhibitors there may be in the seed, even if the fruit is still on the seed.

Conclusion
Keeping seeds alive requires the consideration of many important physical and chemical factors. We now know enough about the manipulation of storage environments to at least minimise undesirable changes in most palm seeds for up to several years for some species. Yet many so-called short-lived seeds do not retain their viability even under the best known procedures and ongoing study is required.

Communal Pots for Palm Seedlings

Growing large numbers of palm seedlings economically

This was originally posted on the Trebrown forums in 2006. The thread is now closed. However, you’re welcome to leave a comment on this blog.

"I have large quantities of Phoenix sylvestris, Phoenix loureiri var. humilis, and Phoenix reclinata. I would prefer to avoid planting each seed into individual pots, as this would be very costly and time consuming on my part, so I’d like to grow them directly in the soil. Would it be possible to sow them directly into the soil, or should I try the ‘baggie’ method and then transplant directly into the ground when I see signs of root growth? Would either of those give good results? I’ve already got some Phoenix canariensis in baggies that have sprouted, and I’ve put half of them in pots – the other half are still in the bag as I’m wondering if I shouldn’t just stick the rest in the ground. Any help with this would be appreciated."

Well! I guess the first question should be; Where are you? If you’re in a reasonably warm climate then you stand a good chance of germinating them in the ground. Phoenix generally germinate better when planted in pots rather than by using the poly bag method. They need quite a bit of moisture, which when given to them in the bag tends to rot them faster. They need heat. Around 30°C (90°F) you might get away with about 25°C but germination will be slower and you may have some losses. So if you can maintain these temperatures in the ground then they will germinate. They are not too fussy about soil types. The main problem you’ll have by planting them directly into the ground will be losses through animals eating them.

"Thanks so much for your reply. I live in the US in North Florida – some sources say US zone 9a, others say zone 8b. It’s pretty warm here (averaging mid 70’s to low 80’s F, with evening temperatures in the high 50’s to low 60’s right now). I would assume it’s not warm enough to get them to germinate directly in the ground right now? Perhaps sow them in flats and transplant into the ground when they show signs of growth? My soil is quite sandy and somewhat dry, which would make germination even more difficult I’d think, unless I were to amend the soil where I’d plant. I’m primarily concerned with having to place them all into pots, as with the amount of seeds I’ve got, it would prove to be very costly and time consuming on my part. Jason."

Hi Jason! Yes! You’re better off planting them in pots. But not flats though! Especially the P. silvestris. You’ll find that these will send down radicals to about 12" to 18" from the outset. That will make it very difficult to prise the roots out later. The best way to handle Phoenix on a mass scale is to plant them in very deep communal pots. Get a deep pot and place a piece of fabric over the holes in the bottom. Then fill the pot ¾ full with a coarse sand or grit about 4mm. Then the last quarter fill with compost. Throw the seeds on top. They can completely cover the surface and be piled two seeds high. Then cover with about 1" of compost. Place the pot on a hotbed about 90°F, water well and cover with plastic. Depending on the species, the seeds will germinate on mass in about 1 or 2 months. Water regularly (being such a well drained medium, you’ll need to water daily). After about a year in that pot there will be a mass of roots. But not to worry about that, the roots will easily lift out of the coarse sand with minimal damage. You might want to place a few stones on top of the seeds to hold them down and force the roots through the sand. They have a tendency to push themselves right out of the pots.

"Your technique for starting them sounds really good to me – I will try it that way and definitely report back with how it worked out! You’re sure that it’s a good idea to leave them in the pots like that for a year though? Will they not set out leaves after a couple months? That’d be quite a tangled mess I would think, but at least it gives me some time to figure out if I should then pot them up individually or just plant them in rows in the ground. What say you? Anyhow, thanks a ton for your advice – it’s much appreciated!"

Jason I raise 10s of thousands of Phoenix seedlings every year! There is no other way to do this more effectively. There will be a lot of roots, but if you have a deep enough pot the roots will be mainly straight. I didn’t mean to say ‘lift them out’ in the last thread. I’m just used to saying that. You can’t pull them out. You tip the pot on it’s side and gently pull the plants. The sand will just fall off the roots. The longer (up to about 24 months) you leave them alone the less plants you will loose through transplant shock.

One thing I ought to mention is feeding! For the first year and part of the second the plants take all of their food from the seed. After that time they will require feeding on a regular basis, because the sand holds nothing for them. It is usually better to lift them after the first year. Even young (two year) seedlings would get eaten if you transfer them to the ground. You would be better off potting them on. Despite what some people say about under potting palms, Phoenix like over potting in deep pots, and plenty of water during the growing months.

Communal Pots

I’ve had people ask about the method of growing palms in communal pots. So here is an example of the best way to handle Phoenix palm seedlings on a mass scale – Plant them in very deep communal pots. Get a deep pot and place a piece of fabric over the holes in the bottom. Then fill the pot ¾ full with a coarse sand or grit about 4mm. Then the last quarter fill with compost. Throw the seeds on top. They can completely cover the surface and be piled two seeds high. Then cover with about 1" of compost. Place the pot on a hotbed about 90°F, water well and cover with plastic. Depending on the species, the seeds will germinate on mass in about 1 or 2 months. Water regularly (being such a well drained medium, you’ll need to water daily). After about a year in that pot there will be a mass of roots. But not to worry about that, the roots will easily lift out of the coarse sand with minimal damage. You might want to place a few stones on top of the seeds to hold them down and force the roots through the sand. They have a tendency to push themselves right out of the pots. Adriaan asked:

a) For which species can I use this method of (mass) planting?
b) How deep should the pots be to give the roots plenty of space for growing in a straight line down?

To answer the second question first; Always as deep as possible! This depends on the species, some species produce very long roots from the outset, up to 60cm (2 feet) long. Others produce much shorter roots. You need to know what the species you’re growing requires. But It’s generally better to provide a deeper soil than you need. The answer to the first question is much more general; I grow most species of palm using similar methods, but not all. Some species, and I’ll use Bismarckia nobilis as an example ought to be planted individually in their own deep pots, because deep rooting species like this don’t like having their roots disturbed. But for most other species; they get planted in my nursery in one of two ways; The one I’ve already mentioned, using a lot of sand, and for species with a more tropical requirement, and where they require better water retention in the soil I use only ¼ of sand in the bottom of the pot with the rest of the pot filled with compost. With Phoenix and several other species; The seeds can be sown directly into the pots. But most species of palm require some kind of pre-sprouting method like the ‘baggie’ method with applied heat.

"Thanks for you answer. But, when I use this method, is there no problem with the small leaves? Example; Trachycarpus fortunei will make some wide leaves, is the space for the leaves no problem? And a pot of 60cm deep? That’s almost impossible to handle. Can you give some more specific depths for some species like : Cycas revoluta, Wodyetia bifurcata, Dictosperma album, Trachycarpus fortunei, Phoenix canariensis, Phoenix loureiri var humilis, Phoenix roebelinii, Roystonea regia, Ravenea rivularis, Chamaerops humilis, Archontophoenix alexandrae, Hyophorbe lagenicaulis, Hyophorbe verschaffeltii, Pachipodium lamerei and the Pritchardia thurstoni? I hope you can give 1 or 2 depths which I can use for most species. And I assume that this method wont work with cycas revoluta and wodyetia bifurcata seeds, or do you think that will work also? Thanks Adriaan."

Hi Adriaan. That’s a lot of questions for one thread! The first bit about the leaves; I don’t really understand! Palms being Monocots start life by producing a single strap leaf. They will produce about five strap leafs before they start producing their true leafs. In the first year (depending on species) they will only produce 3 or 4 leafs. The mass planted seedlings look like grass growing in the pot. Yes! Deep pots are always hard to find. But if you’re growing on a really large scale you can use large bins. On a smaller scale, try using specialist palm pots or rose pots. It’s not too expensive to fill these pots because you’re using mainly sand. Wodyetia bifurcata does very well in communal pots. But I grow my Cycads in individual pots. I know some people do grow Cycads in communal pots. I won’t answer your question here for all the different species you mentioned. It would get too long! But one I ought to mention is Ravenea rivularis. I grow these in communal pots with a lot of sand, but these really need a lot of water, so you must remember to keep watering them. For the other species; you need to think of their requirements. Are they deep rooting species (radicle forming)? or are they shallow rooting species? Do they require a very well drained soil or do they require a good water retaining soil? These answers can be found in books about the individual species or you can ask here about a particular species. But I generally give each species a few cm deeper soil then they will use.

"What is best method of mixing your own potting soil for: A) sowing seeds and B) replanting palm seedlings? I live in the Caribbean (hot climate all year. What should I include to make the seedling grow healthy and good? Please include quantities for your suggestions. Hamilton."

Hamilton, I make all my own seed and potting mixes. For many palm types the seed mix should not contain any loam (garden soil) for some it is OK but I don’t for any palm seeds. The best seed mix is simply 50% peat or cocofibre and 50% course sand. That works well for most palms, but I make a 70% peat to 30% sand mix for some of the more tropical and water requiring palms. For potting on it’s more complex, but I try to replicate the natural environment’s soil from the origins of the palm as much as possible. A potting mix should be rich in all trace elements and as deep as possible.

Deep Pots

If you live in the USA there are a couple of manufacturers of very deep pots. Namely, Steuwe and Anderson Die. I have considered importing these into the UK before, however I’m still not sure if the extra cost is justifiable. Deep rooted palms do pose a real problem, because a relatively small plant requires an exceptionally deep pot, and if you were to use an oversized pot for these it over inflates the cost of the plant commercially. Flower buckets make excellent communal pots for sprouting palm seeds on mass. We use plastic fish boxes or other similar boxes commercially for this purpose. But this doesn’t provide an answer for potting individual palms. Although the flower buckets are suitable for some of the larger species. For potting on we have taken to using the black expandable gusset polythene pots that were popular a decade or more ago in the nursery trade. The commercial sizes are not suitable so we have these manufactured to our specifications. I.e. we have the standard commercial sizes but we add 2 to 3 times the height to the pot. The drawback is that expanding palm roots will soon split the bags. But we use that as an advantage and plant the bag with the plant in larger pots as and when needed. This aids the plant by minimising root disturbance during re-potting. These expandable gusset pots also offer a number of other advantages i.e. the much cheaper cost, and you can cram a lot more plants on to a single growing bench allowing minimal run off of liquid fertiliser.

I can only think of one instance where one would plant seeds direct into the poly pots. That is for Jubaea. Those seeds are sprouted first then planted in 1-litre narrow poly pots which are filled only with sand. The sand prevents rotting which so often happens with Jubaea, and of course seedlings don’t require any nutrients in the soil, as they get all that they need from the seed. As soon as the roots start breaking through they are potted on, bag and all in a proper growing medium. I suppose you could do the same with Brahea, Bismarckia, Borassus, Attalea, Butia, Corypha, Hyphaene and many more of the exceptionally deep radicle forming species. We don’t though; we plant all the higher value deep rooting species direct into their own rigid pots from the outset. Butia are communally planted. The gusseted poly bags are used almost exclusively for potting-on until a deep rigid pot is justified.

"When can I move my seedlings outside?

I now have various palm seedlings in pots on windows sills and in propagators around the house from seeds I bought from you. Now that I have bought a greenhouse, would you be able to advise at what time of year I could bring some of these outside into the greenhouse. I have all sorts from individual Euterpe edulis pots to communal pots of 100’s of Washintonia (looks like grass) Also, does a greenhouse speed up the growing process? As you advised in another thread seedlings grow about 4 strap leaves per year and I just wondered what helps this speed up; i.e. direct light from a lamp on the plants when in the house in the winter? Thank you Douglas."

Hi Douglas, It’s the number of Growing Degree Days (GDD) in the year that will make your palms put on the most growth. So obviously you’ll maintain those temperatures better indoors or under glass than you will outdoors. Your glasshouse may not be as warm as your house at this time of year, so you’re better at making the decision when to move them. Your glasshouse will maintain better light and humidity than your house though, and your palms will welcome that. Your potting on from the communal pots is very much different for each species. At most you would only want to leave them communal for 2 years. But the Washingtonia and Euterpe are very fast growers and you should over pot these now, feed them well and stand back and watch them grow, both require a lot of water during the growing months.

"Thanks for your response Phil. Does that mean each individual strap leaf plant needs to go in its own pot or could I just take the rose pot I’ve got 100’s in and pot into an even bigger pot? Thank you Douglas."

Hi Douglas, If the plants are too crowded then they will self thin themselves out until only the one strongest plant remains. They not only need to be potted up individually, but they need to be done with care not to damage the roots, and they’ll need very deep, over sized pots. If you’ve followed my advice from above then you will have planted those Washingtonia communally in very deep pots or boxes. In the bottom half of the pot would have been course sand. Now when you gently lift the seedlings out you will find that the sand falls off the roots, and with a little gentle prying you will be able to separate all the seedlings without damaging any of the roots. When a palm root gets damaged, then that root will die back to the base of the stem, where a new root will grow to replace it. If you damage all the roots (and there are probably only 2 roots per seedling) then the plant has no roots, and will die before it has chance to put out any more. Palm roots are not like other tree roots. You can’t prune them in the hope of making them bush up. This is the same for mature palm trees. If you want to transplant a mature palm you should dig around the tree one year, then return the second year to under cut. This will permit new root growth around the surface of the soil from the first lot of damage, and mean that the tree has a new set of roots to carry it through the transplant. You must find the deepest pots you can find for your Washingtonias. The same is true for all desert palms. These send down long roots through the sand in search of water, and you need to accommodate these roots as best you can. And despite what I’ve heard some people say, Washingtonia will grow very very fast if they’re over potted in large pots, well fed, and given plenty of water during the growing months.

Climate adaptedness in palms

Predicting Cold Hardiness in Palms

Climate adaptedness, I feel is a better term than Cold hardiness

The nature of one’s growing season has a profound effect on “cold hardiness”. Cold hardiness zone maps will provide indicators as to the minimum temperature a species may have been subjected to. However, that data is insufficient. Therefore, we must look at the physical map for that specie’s natural distribution range where this will indicate many other vital statistics; Latitude, Altitude, and environment type. The environment type indicates the amount of vegetative cover, topography, total sunshine in hours, total rainfall in mm, number of rainy days, etc..

Thermally, the summers of climates that have some cold weather limitations in winter fall into three groups:

Group 1: warm – daytime temperatures in summer are consistently warm and remain elevated during the night. Over 2500 GDD per annum* (semi-tropical and low desert climates).

Group 2: mixed – warm daytime temperatures in summer may be mixed with cooler days or cool mornings. There is a considerable drop in temperature during the night. 1000-2500 GDD per annum* (warm Mediterranean and semi-arid inland climates).

Group 3: cool – warm daytime temperatures are the exception rather than the rule. Nights are consistently cool. Fewer than 1000 GDD per annum* (mild maritime and subtropical montane climates).

We should then breakdown this still further, by including specific local environment conditions at that local; I.e., Latitude, Altitude, and environment type.

All of these group examples above are “Hardiness Zone 9b” climates, all very different. Whether or not any given palm will adapt to the given winters depends, in large part, on how thermophilic the palm is, not just on how well it tolerates occasional frost, which is how most people read hardiness zones to be. Rhopalostylis sapida, for example, is not thermophilic at all. It grows slowly in temperate conditions and giving it additional heat does not accelerate its growth. Butia capitata is moderately thermophilic. It grows slowly in temperate conditions but prefers subtropical conditions and giving it additional heat does accelerate its growth. One could classify “cold-hardy” palms as belonging to climate group 1, 2, or 3 depending on what kind of summers they prefer. The problem with the recognised list of “temperate palms” is that it mixes palms from all three groups with little regard for limitations imposed by the nature of the growing season, and environment type associated with the specific specie.

Another limiting factor is seasonal precipitation. In ideal conditions, most palms would prefer equi-distributional rainfall. With cold winters, however, dry winters are best and a strong rainfall peak in spring or summer produces the best growth. Having a marked rainfall peak in winter adds another limitation to what kind of palms will grow in a “temperate” climate.

*Growing Degree Days per year calculated on a base of 12°C. As the temperature most temperate palm species commence growth.

GDD are calculated by taking the average of the daily maximum and minimum temperatures compared to a base temperature, Tbase, (usually 10°C). As an equation:
GDD calculation
GDDs are measured from the winter low. Any temperature below Tbase is set to Tbase before calculating the average. Likewise, the maximum temperature is capped at 30°C because palms generally do not grow any faster above that temperature.
For example, a day with a high of 23°C and a low of 12°C would contribute 5.5 GDDs.
GDD example

Example climate models compared with Cornwall in the United Kingdom.

Here we examine examples of the climate models for species:

Climate at Trebrown Nurseries, Cornwall, UK. (12 Months. Hardiness zone zone 9b).
Sunshine (Hours) 2h 3h 4h 6h 7h 7h 6h 6h 5h 4h 2h 2h
Av. Night Temp. 4°C 4°C 5°C 6°C 8°C 11°C 13°C 13°C 12°C 9°C 7°C 5°C
Av. Day Temp. 8°C 8°C 10°C 13°C 15°C 18°C 19°C 19°C 18°C 15°C 12°C 9°C
Precipitation 99mm 74mm 69mm 53mm 63mm 53mm 70mm 77mm 78mm 91mm 113mm 110mm
Rainy Days 19 15 14 12 12 12 14 14 15 16 17 18
Winter Spring Summer Autumn Winter
Record min. temp. -8°C. But this was a one-off. Otherwise -4°C. 887 GDD per annum

Total sunshine hours = 1620, Total rain = 950mm. Total rainy days = 178.
So from this data we can see that despite the large amount of rain, the UK still gets a reasonable amount of seasonal sunshine. For those who don’t already know this, this makes the UK a great place for gardening. This amount of sunshine is attributed to the long summertime day length, a consequence of being so far north of the equator. The downside is the minimal sunshine during the winter months, combined with the fact that most of the rain falls in the winter. There is little summertime extreme heat, and little temperature swing between summer and winter. The winters are extremely mild. Finding palm species, that thrive in these conditions is challenging.

Chamaerops humilis. Climate in Madrid, Spain. (12 Months).
Example: Mediterranean
Sunshine (Hours) 5h 6h 6h 8h 9h 11h 12h 11h 9h 6h 5h 5h
Av. Night Temp. 2°C 2°C 5°C 7°C 10°C 15°C 17°C 17°C 14°C 10°C 5°C 2°C
Av. Day Temp. 9°C 11°C 10°C 18°C 21°C 27°C 31°C 30°C 25°C 19°C 13°C 9°C
Precipitation 39mm 34mm 43mm 48mm 48mm 27mm 11mm 15mm 32mm 53mm 47mm 48mm
Rainy Days 8 7 10 9 10 5 2 3 6 8 9 10
Winter Spring Summer Autumn Winter
Record min. temp. -10°C. for this provenance. 1551.2 GDD per annum

Total sunshine hours = 2790, Total rain = 445mm. Total rainy days = 87.

Madrid is better compared with London rather than Cornwall, because London shares the same average Min. Temp. (2°C), and the same record Min. Temp. (-10°C), both being a zone 9a. Here in Cornwall, we actually have a better hardiness zone than both those zone 9b. We all know that Spain is a better place to grow palm trees, so why is that? – 58% more sunshine than the UK, this almost entirely due to the 91 fewer rainy days. The consequence of this being far less available water, 505 mm less than the UK. Making this climate hot, dry, and arid.
Chamaerops humilis will grow almost anywhere in the British Isles, and we don’t ever get temperatures low enough to harm it. However, it grows very slowly here.

Butia capitata var. odorata. Climate in Uruguay. (12 Months).
Example: Campos (Grass-land).
Sunshine (Hours) 5h 6h 7h 8h 10h 10h 11h 10h 9h 8h 6h 5h
Av. Night Temp. 6°C 6°C 8°C 9°C 12°C 15°C 17°C 16°C 15°C 15°C 9°C 6°C
Av. Day Temp. 14°C 14°C 17°C 20°C 23°C 26°C 28°C 28°C 26°C 26°C 18°C 15°C
Precipitation 47mm 66mm 99mm 99mm 84mm 81mm 74mm 79mm 76mm 66mm 74mm 79mm
Rainy Days 6 7 6 6 6 7 6 5 5 5 5 5
Winter Spring Summer Autumn Winter
Record min. temp. -4°C. for this provenance. 1961.8 GDD per annum

Total sunshine hours = 2850, Total rain = 951mm. Total rainy days = 71.
So this is basically a Mediterranean climate, but with twice the rainfall over fewer rainy days. The rainy days are also spread quite evenly throughout the year, providing excellent growing conditions, with a long growing season. The exact same amount of rain as the UK, but fewer rainy days, which in turn produces more sunshine hours. It is clear why Butia capitata grows so well in the UK. With more sun it would be completely at home here.

Washingtonia filifera. Climate in Arizona, USA. (12 Months).
Example: Arid Desert.
Sunshine (Hours) 8h 10h 11h 12h 13h 14h 13h 12h 12h 10h 9h 9h
Av. Night Temp. 4°C 6°C 8°C 12°C 16°C 21°C 25°C 24°C 21°C 13°C 7°C 4°C
Av. Day Temp. 18°C 21°C 24°C 28°C 33°C 38°C 40°C 38°C 36°C 30°C 24°C 19°C
Precipitation 20mm 20mm 18mm 10mm 3mm 3mm 25mm 25mm 18mm 10mm 15mm 23mm
Rainy Days 4 4 4 2 1 1 6 6 3 2 3 4
Winter Spring Summer Autumn Winter
Record min. temp. -13°C. for this provenance. 3315.4 GDD per annum

Total sunshine hours = 3990, Total rain = 190mm. Total rainy days = 40.

At first glance at the record min. temp. -13°C., and climate zone 9a most people will assume that Washingtonia filifera will grow easily in the UK. This palm is adapted to a very harsh and arid environment. It likes a lot of sun, high temperatures, dry air, and any cold snaps to be very short. It does like its roots in plenty of water, but it totally dislikes freezing moist air, and for this reason this palm can be killed at a mere -4°C in the UK. It can be grown in the UK, but requires a little attention.

Parajubaea torallyi var. torallyi. Climate in Pasopaya, Bolivia. (12 Months).
Example: Tropical, High Mountain.
Sunshine (Hours) 9h 8h 7h 6h 6h 6h 6h 5h 5h 6h 8h 9h
Av. Night Temp. 1°C 2°C 3°C 4°C 6°C 6°C 6°C 6°C 6°C 4°C 3°C 3°C
Av. Day Temp. 17°C 17°C 18°C 19°C 19°C 18°C 17°C 17°C 18°C 18°C 18°C 18°C
Precipitation 10mm 13mm 28mm 41mm 48mm 94mm 114mm 107mm 66mm 33mm 13mm 8mm
Rainy Days 2 4 9 9 11 18 21 18 16 9 5 2
Winter Spring Summer Autumn Winter
Record min. temp. -4°C. for this provenance. 1064.5 GDD per annum

Total sunshine hours = 2430, Total rain = 575mm. Total rainy days = 124.

This is a climate comparable to the UK except for the fact that the temperature swings between Min., & Max. temperatures occurs between day and night within a single day, not summer and winter seasons, as in the UK. We can assume that Parajubaea torallyi dislikes seasons, or it would have migrated south down the Andes mountain range after the last Iceage. And we can assume that this palm dislikes high temperatures, or it wouldn’t be growing at such a high altitude in the tropics. Parajubaea torallyi grows at the highest altitude of any palm (3,400 m).
Parajubaea torallyi seems to tolerate the UK temperatures, because we have minimal temperature swing between summer and winter. However, it grows very slowly.

Rhopalostylis sapida. Climate in West, South Island, New Zealand. (12 Months).
Example: Wet Temperate.
Sunshine (Hours) 4h 5h 5h 5h 6h 7h 7h 6h 5h 5h 4h 4h
Av. Night Temp. 3°C 3°C 6°C 8°C 9°C 11°C 12°C 12°C 11°C 8°C 6°C 3°C
Av. Day Temp. 12°C 12°C 13°C 15°C 16°C 18°C 19°C 19°C 18°C 18°C 14°C 12°C
Precipitation (mm) 218 239 226 292 267 262 262 191 239 239 244 231
Rainy Days 16 16 17 19 18 16 14 12 14 14 15 15
Winter Spring Summer Autumn Winter
Record min. temp. -5°C. for this provenance. 642.5 GDD per annum

Total sunshine hours = 1890, Total rain = 2910mm. Total rainy days = 186.

Here we have a climate almost exactly the same as the UK, except for the massive 1960 mm of additional rain falling in almost the same umber of wet days as the UK. This is the southernmost range of Rhopalostylis sapida on mainland New Zealand, and is the ideal provenance to grow in the UK. This palm also grows in areas of New Zealand with much less rain than this. Nevertheless, we can assume that the rain in the UK would not deter this palm from thriving here. The palm seems to prefer higher temperatures if it can get them, and temperatures below -5°C. can easily kill it. Rhopalostylis sapida grows very slowly both in the British Isles and New Zealand.

Trachycarpus fortunei. Climate on Zhoushan Island, China. (12 Months).
Example: Temperate.
Sunshine (Hours) 4h 4h 4h 5h 5h 5h 7h 7h 5h 6h 5h 5h
Av. Night Temp. 1°C 1°C 4°C 10°C 15°C 19°C 23°C 23°C 19°C 14°C 7°C 2°C
Av. Day Temp. 8°C 8°C 13°C 19°C 25°C 28°C 32°C 32°C 28°C 23°C 17°C 12°C
Precipitation 48mm 58mm 84mm 94mm 94mm 180mm 147mm 142mm 130mm 71mm 51mm 36mm
Rainy Days 6 9 9 9 9 11 9 9 11 4 6 6
Winter Spring Summer Autumn Winter
Record min. temp. -12°C. for this provenance. 2113.9 GDD per annum

Total sunshine hours = 1860, Total rain = 1135mm. Total rainy days = 98.

Here we have the climate, which is the best match to the UK. This particular provenance of Chusan Island is wetter and sunnier than the UK, but if you compare the average climate over the whole, wide range of Trachycarpus fortunei in China then you will find that it matches the UK very well. Trachycarpus fortunei enjoys the longer day length in the UK summer, and it can be said that the palm actually grows better in the UK than it does in China.

Summary

Finding an exact match to the UK climate is impossible, due to the fact that the British Isles lies so far north of the equator, where both winter and winter nights are long. No other place on the planet, which shares similar winter temperatures is situated so far from the equator. Studying hardiness zones alone does not indicate species suitable for growing in the UK. All palms, which can be grown here would prefer more winter sunshine than they can find in the UK. On the plus side; the British Isles’ mild winters permits us to grow more species, albeit uncomfortably than any other place situated this far from the equator, 50°N – 60°N. Studying climate modelling statistics of palm’s provenance’s in this way has so far identified over 130 (and counting) species as likely candidates for trial in the British Isles. But only by actually trialing them in the ground here can we identify the specie’s tolerances.