The cultivation of palms.
The germination of palm seed.
As it ages most palm seed quickly loses it’s viability, especially the seed of rainforest varieties e.g. Chamaedorea costaricana. As these seeds fall into the moist humus of the forest floor they are never subjected to drying out. If these seeds are collected fresh and planted without being allowed to dry out they should germinate easily. They must never be stored dry for any length of time.
Seed from varieties that grow in dry regions e.g. Washington robusta, usually have a longer period of viability, they can be left longer before planting and can tolerate being stored dry. However fresh seed will always yield better results.
When palm seed is first collected the pericarp (outer fleshy layer) should be completely removed. The pericarp on some seeds contains germination inhibitors which must be removed before the seed will germinate, also as the pericarp decomposes it may cause the seed to rot.
Soaking the seeds in water for several days will soften the pericarp making it easy to remove. It is important to change the water at least every 24 hours to prevent bacterial growth occurring which may cause the seed to rot.
Once cleaned the seeds can be sown in a well drained growing medium, this can take the form of a commercial potting mix or a light friable soil. Cover the seeds with just a few millimetres of the chosen medium, water well and keep moist for the period of germination.
If seeds are planted too deeply they will most likely rot before they germinate. Regardless of the size of the seed it should only be covered with a few millimetres of growing medium. Germination may take from a few days to four or more years during which time it is vital that the seeds are never allowed to dry out as this could well be fatal to them.
For shade preferring or rainforest palms such as Chamaedorea, Linospadix and Archontophoenix the seed is best sown in plastic pots of 100mm to 200mm diameter with a depth of around 150mm. The seedlings of these varieties do not send down long tap roots so they don’t require very deep pots or trays.
Palms from dry regions or places with seasonal rainfall such as some species of Phoenix, Butia, Jubaea, Parajubaea and Livistona all produce a large anchoring root (hypocotyl) and require pots with a depth of at least 200 mm to accommodate this root. If seeds from these varieties are germinated in shallow pots the hypocotyl may reach the bottom of the pot and push the seed up out of the soil mix before the seed has fully germinated.
Another method that can be employed to germinate seed is to place the seed into a sealed plastic bag with a moist and sterile medium such as untreated saw dust or vermiculite. Place the bag in a warm position such as in a hot water cupboard. Occasionally open the bag to allow fresh air in, this will help to prevent fungus and rot from developing which may infect the seeds. Avoid using polystyrene trays for seed raising as it is likely the roots will grow into the polystyrene and will be very difficult to remove without damaging the root which will usually result in the death of the seedling.
Tropical palm seed normally requires temperatures between 25 and 35 degrees C (77 – 95 degrees F) for germination, warm to temperate varieties germinate more successfully between 22 and 28 degrees C (72 – 82 degrees F). High range (35 degrees C) temperatures may damage seeds from cooler regions.
Palms from high altitude areas , such as species of Ceroxylon, Parajubaea and Catoblastus germinate best in the 15 to 22 degree C (59 – 72 degrees F) range. These seeds will rot readily at temperatures above 25 degrees C (59 – 72 degrees F).
Raising palm seedlings.
When the palm seeds have germinated the resulting seedlings will survive on the food stored in the endosperm until such time as that food supply is exhausted. Now they must be able to extract there own food requirements from the soil with there newly formed roots. If the soil is poor and lacks the nutrients and specific minerals that the seedlings need, they will collapse and die at this stage, unable to establish dependancy on outside nutritional sources. As soon as the seeds have germinated, a feeding program should begin using a general purpose liquid fertiliser at fortnightly intervals.
Palm seedlings may fail when they have used up all the nutrients in the seed endosperm and they are making the transition to nutrients supplied by the soil. This will occur if the soil is deficient in the nutrients that the palm seedling requires. Seedlings that make a healthy start are usually more vigorous growers, will resist disease and will have better cold tolerance than those with a start that has been interrupted by a lack of nutrition.
Some palms have special nutritional requirements such as highly mineralised soil so for this reason it is very good practice to feed them regularly with a fertiliser which is rich in trace elements and minerals.
Palm seedlings can be separated and planted in individual pots or planter bags (I prefer to use a pot with recessed drainage holes which won’t block up easily) when the first leaf has fully formed. At this stage the seedlings roots have formed sufficiently but the seedling is still easy to remove. Do not allow the seedlings to develop much beyond this stage before separating and potting as some species resent root disturbance and may ‘set – back’ for a period of time before they regain there growth vigour.
The seedling should be potted into a pot or bag which is large enough to accomodate it’s roots without them growing into a tangle in the bottom of the pot. When a palm is going to be grown as an indoor plant choose the smallest size pot possible to accomodate the roots, this will keep the palm from becoming large to quickly so that it can remain as an indoor plant for longer.
When palms are being raised for outdoor planting, the intention is to grow them in the most vigorous way possible and the roots need to be encouraged to develop fully ; to grow downwards and outwards to take full advantage of the available soil and food. With cultivation for outdoor planting, palms should be repotted before becoming root bound in there existing pots. Some varieties of palms i.e. Jubaea Chilensis and Parajubaea Cocoides, resent having there roots crowded, if planted into small containers and there roots become restricted,there growth becomes very slow and they may take some time to return to a normal rate of growth.
Planting in the ground.
Before planting your palm in the ground you should first consider it’s needs
- Does it prefer sun or shade?
- Will it tolerate an exposed site or should a sheltered site be chosen?
- If the palm has been grown in a shade house has it been hardened off to cope with going into full sun?
Palms should be planted in there permanent positions when they are vigorous and healthy, spring and summer are the best times for planting.
Dig a hole that is at least two or three times the size of the root ball,into the hole mix compost 50/50 with good soil and some well matured animal manure. Compact this down lightly, then dig out of this a hole for the root ball. Before the palm is placed in the hole fill the hole with water and allow it to drain away. Plant the palm with about 50mm of soil covering the root ball, back fill with the improved soil mix, firm down, water well and cover with a layer of mulch. For taller palms staking may be necessary for the first one or two years until the roots have grown enough for the palm to support itself in windy weather.
In wet climates or in areas susceptible to flooding it is advisable to mound up the area slightly to create a raised piece of ground for the palm to be planted on. This is especially recommended for palms that need a little extra warmth until they are established or in areas with heavy poorly drained soil. In dry climates, palms can be planted in a dip slightly below ground level so that a shallow trough is formed around the palm to channel water to the roots.
During the hottest and dryest months , water deeply and regularly and feed the palm to encourage strong growth. Shallow watering will only bring the roots to the surface where they will dry out.
Palms benefit greatly from a good thick layer of mulch over the root ball. This retains moisture and keeps the soil at an even temperature. Suitable materials to use as mulch are wood chips, river stones, pine bark, straw and compost.
Palms will survive in poor infertile soils, but there growth rates will be slower and there general condition and appearance not as good. They are heavy feeders and will respond vigorously to rich cultivated soil, plenty of water and regular applications of fertiliser. Even those palms that naturally occur in locations with poor soil respond well to rich moist soil in cultivation.
Once a palm is established many of the feeding roots are near the soil surface and so there response to fertiliser is fast. Young palms respond to regular feeding with both organic and inorganic fertilisers such as liquid seaweed, liquid blood and bone, animal manure and propriety brands of fertiliser. Their growth should be kept vigorous to produce healthy plants, this is particularly important with the more tender species that they should grow strongly and maintain health during the summer months. If they are healthy they are more likely to survive the coming winter months.
Fertiliser should be applied in early spring and again in summer and early autumn. As much as 5 to 10 kg can be used for a very large palm and should be scattered in the area under the spread of the palms leaves. With large amounts of fertiliser it is better applied in two or more applications allowing a few weeks between each application. For smaller palms up to five metres tall the application rate of fertiliser should be from 0.25 to 2 kg per season and once again should be applied in two or more applications.
Fertiliser, especially inorganic fertiliser, should be applied when the ground is moist and just before rain.
Various types of fertiliser can be used provided they contain the three main elements, nitrogen (N), phosphorus (P) and potassium (K) with magnesium (Mg) and other trace elements included. In wet climates, animal manures such as cow, poultry and sheep manure can be applied as a supplementary top dressing and mulch which will be slowly washed into the soil by the rain. This dressing should be kept away from the palm trunk, not piled up against it as this may likely cause collar rot to develop.
Fertiliser for palms should ideally have an NPK ratio of 3:1: 3. This is a ratio and not necessarily the number on the fertiliser bag, this would rather be something like “15:5:15” or perhaps “12:4:12.