Palms are unique among woody ornamental plants because, with few exceptions, palm species can only be propagated from seed. Palms are also "notorious" for slow and uneven seed germination.
It is estimated that more than 25% of all palm species require more than 100 days to germinate and less than 20% actually sprout.
The main reason for this is that the seeds of most species have small or "immature" embryos. These must first fully develop before they can eventually germinate. Nevertheless, the germination success of palm seeds can be maximized by following a number of basic guidelines.
In this blog, you will find various practical tips to help your own palm seeds germinate as well as possible. And above all, to enjoy your new palm seedlings.
Palm seeds vary greatly in size. Many palms have seeds no larger than 60 mm in diameter. Meanwhile, the largest seed – of any flowering plant in the world – is that of a palm; the double coconut, Lodoicea maldivica. Most of a palm seed consists of nutritive tissue called endosperm. Endosperm supplies food to the germinating seedling for a longer time than most flowering plants (Figure 1). The “milk” and the white flesh of a coconut are liquid and solid endosperm. The palm embryo is very small, either cylindrical or cone-shaped. The seeds themselves can be either round or alternately elongated. Their surfaces can be smooth or rougher. Some are wrapped in a hard, water- and air-tight "coat." Fibers from the fruit wall often remain attached to the seed, even after cleaning.
The way palm seeds germinate can be divided into two categories. Category 1 includes palms with "remote" germination (see Figure 2a – c), where the seedling axis develops at some distance from the seed. The first part to emerge from the seed is called the cotyledonary petiole. It resembles the first seedling root but is not. The cotyledonary petiole grows downward into the soil (sometimes very deep) and swells at the base.
From this swelling emerge the first seedling root (radicle or the germ root) and seedling shoot (plumule or the germ shoot). The actual cotyledon or seed leaf remains inside the seed and functions as an absorbing organ called the haustorium. The haustorium transfers nutrients from the endosperm to the young seedling. In palm seeds with "remote" germination, the radicle persists for some time and produces lateral roots. The seeds of Mediterranean fan palms (Chamaerops humilis), Chinese fan palms (Livistona chinensis), date palms (Phoenix spp.), and Mexican fan palms (Washingtonia robusta) exhibit remote germination.
figure 2. (a-f) 2 main forms of palm seed germination
The other main class of palm seed germination is called "adjacent" germination (see figure 2d-f). In these seeds, only a small part of the cotyledon emerges from the seed. It appears as a swollen body that lies against the seed surface and is called the "button." The radicle and shoot emerge from the bottom and top of the button. In palms with adjacent germination, usually the first seedling root or radicle
narrow and very short-lived. They are quickly replaced by roots formed at the stem base of the seedlings. As with distant germination, a haustorium remains in the seed and absorbs nutrients from the endosperm. Some common palms with this form of germination are areca (Dypsis lutescens), Alexandra palm (Archontophoenix alexandrae), and coconut (Cocos nucifera).
Some palm species (such as Bismarckia, for example) bury the seedling roots deep in the ground (also called taproots). These species require special treatment.
Seeds can be collected from local sources (palm trees in the landscape) or purchased from commercial dealers. Local collection has certain advantages; the freshness, ripeness, and parentage of the seed are known to the collector. If the seed is stored, the collector controls the methods used and the duration of storage. Commercial dealers can usually offer larger quantities and a greater diversity of species. Commercial dealers will also take care of the time-consuming tasks of seed cleaning, which may require special equipment. However, the age and final germination rate of purchased seed are often unknown.
With a few exceptions, palm seeds must be collected when the fruit is fully ripe (in full color), or as soon as it falls from the tree. There are a few exceptions. Palm seeds from green queen palm fruits (Syagrus romanzoffiana) germinate better than seeds from half-ripe or ripe fruit. The cause is probably certain inhibitors in the fruit. Palm seeds from ripe royal palm fruits (Roystonea regia) germinate more slowly than seeds from half-ripe or green fruit.
The viability of palm seeds can vary between trees of the same species, and even from year to year from the same tree. The age of the seed and/or the storage methods used can directly affect the final germination rate. Seeds of some palms generally remain viable for only 2-3 weeks (e.g., Latan palms, Latania spp.), while others can remain viable for more than a year (areca, Dypsis lutescens), as long as they are stored properly. Some growers advocate using a "seed float test." Seeds are placed in water and those that float are discarded because they are less viable. However, some palm seeds naturally float because they are dispersed by water in nature. Moreover, some growers have also found that if the floating seeds are planted, a significant number will still germinate. There are several recognized ways to quickly test seed viability.
Cut open a sample of the palm seeds (figure 3). The endosperm should be firm and the small embryo should fill its chamber (at one end of the seed). The seed is probably not viable if:
figure 3. Cross-section of an aracea palm seed Dypsis lutescens
Left not viable and right viable. Note the shriveled embryo and endosperm in the left seed.
Mix a 1% (10 gm/l) aqueous solution of tetrazolium chloride (available from any chemical supplier). Cut a sample of the seeds in half to expose the embryo and place the half with the embryo in the solution. Leave the jar in the dark for at least 2 hours (sometimes a whole day is needed). If the embryo turns partially or fully red or pink, it is likely viable. If there is no stain, the seed is probably not viable.
The viability of palm seed can also be determined using specialized instruments that measure electrolyte leakage. This is an indicator of the integrity of seed membranes that affect seed viability.
Palm seeds are enclosed by a fleshy or fibrous "husk" / fruit wall (mesocarp). With a few exceptions, the fruit wall must be removed before seeds are stored or planted (Figure 4). Uncleaned areca palm seeds (Dypsis lutescens) are known to germinate if planted immediately after harvest. Coconut seed does not need to be peeled before planting (in fact, the seedling germinates inside the fruit before emerging).
figure 4. palm seed with and without cleaned husk or fruit wall
If only a small number of seeds need to be processed, they can be cleaned by hand. You can cut the fruit tissue away from the seed with a knife. For large quantities, mechanical cleaning is recommended. Palm species (for example areca) with relatively thin fruit walls can be easily cleaned. You rub the seeds over a strong, large mesh screen while rinsing them with a hose to remove the mesocarp. Or you rub the fruit wall off by hand in a bucket of water.
Some palm species contain an irritating substance in the pulp (calcium oxalate crystals). Cleaning these seeds by hand can be a painful experience. It is recommended to wear gloves when handling these fruits:
Most palm seeds need to be soaked in water to first soften (ferment) the fleshy fruit wall (figure 5). The water should be changed daily if possible. The fruits are ready for processing when the mesocarp easily yields when squeezed with the fingers.
figure 5. palm seeds being soaked in buckets of water to soften the mesocarp
The fruits are then placed in a seed cleaning machine that scrapes the fermented mesocarp around the seed. The pulp is washed out of the cleaning chamber and collected. A small cement mixer partially filled with coarse sand or gravel works quite well (figure 6).
figure 6. Cement mixer used to clean palm seeds. Gravel inside the machine scrapes the pulp from the seed.
In both cases, water continuously rinses the seeds while the machines operate. Hard or very fibrous palm fruits can be cleaned by mixing the fruits with gravel or stone and repeatedly stepping on them. Similarly, some palm species with very hard seeds have been cleaned by driving a truck or other vehicle over burlap sacks containing the softened fruits. Cleaned seeds should be air-dried for a day or two before storage.
With few exceptions, it is best to plant palm seed shortly after cleaning. If this is not possible, the best general storage procedure is to dust the seed with thiram or captan fungicide. Then seal the seed in plastic bags and store at 18-25 °C. There is evidence that using these fungicides can negatively affect germination. Seeds of most tropical palms lose viability if stored below 15 °C. Some purified seed is known to be stored at 23 °C without loss of viability:
In the case of royal palm, storage for up to 9 months even increases germination compared to planting fresh seed immediately.
Seeds of the jelly palm (Butia capitata) require a period of dry storage for optimal germination. The duration of this period increases with lower temperatures: 90 days at 25 °C, 120 days at 15 °C, and 150 days at 5 °C. Simply removing the hard endocarp in this species and immediately planting the two or three seeds inside resulted in much better germination than dry storage. In general, palms from seasonal climates (versus consistently tropical) may have greater tolerance for storage at low temperatures. Seeds of the silver palm (Coccothrinax argentata) and the thatch palm (Leucothrinax morrisii) can withstand temperatures from -20 °C to 10 °C for a week without loss of viability. Seeds of more tropical species (for example, areca, Dypsis lutescens) can die after 24 hours of storage at 5 °C.
There is much interest in pretreatments that can speed up germination or result in a more uniform germination rate. For the commercial palm grower, the value of seed pretreatments must be weighed against the additional labor costs involved.
A common recommendation is to soak palm seeds in water for 1 to 7 days. It is advisable to change the water daily. The seed should be planted immediately after treatment, as storage after water uptake can cause secondary dormancy. Palm species that respond well to soaking in water include:
Several researchers have reported an accelerated effect on germination by soaking the seed for 1 to 3 days in a concentration of GA3 (a plant hormone). Gibberellic acid (also called gibberellin A3, GA, and GA3) is a plant hormone that promotes growth and elongation of plant cells. However, treatment with this growth regulator causes deformation or excessive elongation of the seedling (figure 7). In some cases, this can even prevent the seedling from sustaining itself. It is not recommended to use a GA3 soak despite any positive effects on germination capacity.
figure 7. Excessive elongation of Areca palm (Dypsis lutescens) seeds on the left, caused by pretreating seeds with a soak of Gibberellic Acid (GA3).
Scarification of palm seeds involves thinning the bony endocarp of palm seeds that can hinder water absorption. This can be done by sanding the seed surface until the endosperm becomes visible, or by soaking the seed for 10 to 30 minutes in diluted to concentrated sulfuric acid (H2SO4).
Scarification can increase the germination capacity of several palm species with hard, water-impermeable seed coats. Complete removal of the stony endocarp, for example, significantly increases the germination rate and speed of Butia capitata. This can be achieved by cracking individual endocarps in a bench vise. The potential risk with mechanical or acid scoring is damage to the embryo during the process. It is best to apply scarification to seeds with hard and impermeable seed coats.
A variety of germination pots can be used for palm seeds, including pots and seed trays. Pots are better than seed trays due to the deeper soil column and better drainage. To provide the extra depth these seedlings need during early development, you can use tree tubes, pieces of PVC pipe, or other improvised pots. These are especially good for very deep-rooted species, particularly those that bury the seedling axis. Some growers prefer to sow seed in large raised beds made of wood or cinder blocks. The most important thing for any germination container is that excess water can drain sufficiently from the substrate.
Substrates for germinating palm seed should be well-drained but still retain some moisture. A pattern of alternating extremes of dryness and wetness is harmful to palm seeds during germination. The particle size in the substrate should not be excessively large and should not be prone to separation with repeated irrigation. A 1:1 volume mixture of peat moss and perlite can successfully aid palm seed germination. The germination substrate mix should be adjusted to the conditions the seed is exposed to. If you want to germinate palm seed in full sun, your substrate requires a higher water-holding capacity than seed germinating in the shade.
The depth at which palm seed should be sown depends on the size of the seed and the species you are growing. Furthermore, environmental conditions determine the planting depth. If seeds germinate in full sun, it is advisable to cover the seed with extra substrate to prevent drying out. However, if the seed germinates in the shade, it is recommended to sow it shallowly. In the case of larger seeds, this means simply pressing them into the soil so that the top of the seed is visible.
The frequency of irrigation also affects the planting depth. Seeds that have germinated in full sun can be planted shallower if irrigation is frequent enough to prevent the substrate from drying out. Additionally, it is best to sow palm seeds with some space between adjacent seeds. Large palm seeds, especially those of difficult-to-transplant species like Bismarckia, are best sown one seed per container.
Almost all palms require high temperatures for the fastest and most uniform germination of their seeds. 20 to 37 °C is the accepted temperature range, and 29 - 35 °C likely produces the best results. Paurotis palm seed (Acoelorraphe wrightii) is known to germinate best at 33 - 38 °C. The keys thatch palm (Leucothrinax morrisii) and silver palm (Cocothrinax argentata) germinate best at 33 - 36 °C. Seeds of the pindo palm (Butia capitata) germinate best within 2 - 3 weeks at 38 °C.
Fluctuating temperatures with 12-hour intervals can increase the total germination of certain species. You could achieve this by using a thermostat controller set to different temperatures throughout the day. This way, you can simulate a day and night rhythm.
Because palm seeds require high germination temperatures, it is best to sow seeds during the warmer months of the year. If the availability of fresh seed makes this difficult, soil temperatures can be increased. For example, you can use soil heat under the germination containers or cover the containers with transparent plastic. Placing the containers on a heat-retaining surface can also raise the temperature by a few degrees. There are also germination chambers (propagators) that perfectly regulate the right temperatures and humidity, allowing you to grow easily all year round.
Many palms germinate in the understory of a forest canopy in their original habitat. Seedlings of these species can germinate in full sun, but their leaves may bleach to some extent under those conditions. Generally, root growth and overall seedling development will improve in full sun. In the shade, seedlings usually have a deeper green color. Some species grow best in the shade (for example, Licuala spp.). Seeds of the Licuala should be germinated in the shade. Seedlings of such species usually bleach severely, burn, and may even die if exposed to full sun. Species native to open habitats show no adverse effects when germinated in full sun. In general, it is necessary to adjust the planting depth of the seed to the light levels the seed will be exposed to.
Palm seeds need consistent moisture during the first critical stages of germination. This is especially true when the cotyledonary petiole or shoot first emerges from the seed. Alternating periods of extremely wet and dry during this time will usually have harmful effects on overall germination rates. If the germination substrate does not have automatic irrigation, it may be necessary to cover the containers with clear plastic to retain sufficient soil moisture. Overwatering can be just as harmful. At no time should standing water be visible on the surface of the germination substrate.
Palm seedlings do not need additional fertilization during the first two months after germination. The endosperm in the seed provides all the nutrition the seedling needs during this period.
The speed at which palm seed germinates, the uniformity of germination, and the percentage of total germination can vary greatly from species to species. Seed of Mexican fan palm (Washingtonia robusta) can start germinating in less than 2 weeks. Seed of the areca palm (Dypsis lutescens) can germinate in 3-4 weeks, while seed of parlor palm (Chamaedorea elegans) may only start germinating after several months and sometimes even after more than a year. You must remain especially patient as long as the seed appears to be in good condition; do not give up hope quickly! Your patience will be tested. Especially when planting palm seed with which you have no previous experience or for which no germination information can be found.
Palm seedlings can be repotted either immediately after germination or after 1 to 2 leaves have formed. The main goal is to reduce the degree of root disturbance in the seedlings. Therefore, it is best to transplant before the roots start circling the container or the roots become entangled with adjacent seedlings. Transplant during the warmer months of the year, when root growth will be rapid.
Seedlings usually have one long root at the time they are first transplanted. Seedlings should first be transplanted from the germination container to a smaller pot that just accommodates the root system and allows for some later root growth. There are pots with essentially open bottoms that, for example, are increasingly used by growers. Palm seedlings benefit from the deeper root run. Long roots that emerge through the opening at the bottom stop growing. This stops the "circling" of roots around the inside wall of the pot. There are then two methods for transplanting the seedlings.
The first method reduces the chance of loss due to overwatering but increases your work. Transplanting into large pots reduces your work and allows for more unrestricted root growth. However, you may experience more loss due to root rot if your seedlings are still small. Palms do not like to be planted too deep, regardless of age or size. For palm seedlings, planting just one and a half cm too deep can result in severe growth delays and eventually the death of the seedlings.
Palm seedlings should be transplanted so that the point of the seedling stem - just above the root system - is at the soil surface (figure 8). This point sometimes has a visible swelling. In palms with adjacent germination, this is the point at the base of the bud. Do not break the connection between the seed and the seedling. If the seed is still attached to the plant by the seed stalk, drape the seed over the edge of the pot or leave it on the soil surface.
figure 8. do not plant your palm seedling deeper than the indicated points
It is sometimes said that you can prune the roots of palm seedlings when transplanting. I definitely do not recommend doing this because it often results in growth delays or even the death of some seedlings. If the seedling root is longer than the new pot, it can be gently bent upwards or around the inner circumference of the pot. A better solution is to use pots that are large enough for the full length of the root.
Some palm species (such as Bismarckia and Borassus) bury the seedling base some distance below the ground. Seeds of these species are usually planted separately in deep pots.
Ideally, newly transplanted seedlings should be placed in light shade (30-50%) for a few weeks. Or until new growth is visible. If this is not possible, the irrigation frequency must be carefully monitored. This prevents the seedlings from experiencing water stress after being placed in a different pot.
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