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.

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.