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.