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Seed Collection, Handling and storage

Like many crops, trees are grown from seed. As such, tree seed collection and handling are critical stages in tree growing and nursery establishment. The seeds must be collected from the right source and be of good quality. However, many people tend to collect seeds which are easy to collect and less attention is given to the quality of the seeds. A very wrong strategy!

What is a seed?

Seeds usually occur in fruits and they are capable of developing into another plant. There are different types of seeds including:

1. Follicle: A dry fruit that splits along one edge e.g Grevillea (Grevillea robusta is a common exotic tree in East Africa, most examples in this post will include cases and species in East Africa, particularly Kenya).
2. Pod: A dry fruit that splits along two edges e.g. Acacia species
3. Samara: A dry fruit with wings e.g. Combretum molle
4. Nut:g. podocarpus
5. Berry: A fleshy fruit with several seeds e.g. Warbugia ugandensis (East African greenheart)
6. Drupe: Fleshy fruit with one endocarp surrounding the seed e.g. Africa olives
7. Cone: Dry fruit with woody scales e.g. cypress species

Mother/ parent trees

Make all attempts to use good quality seeds for your nursery. Good quality seeds can be bought from certified suppliers or they can be collected. If you decide to collect the seeds, ensure that you identify good mother/parent trees. These are the trees which have good quality seeds and are used continuously to provide tree seeds. A mother tree for good seed collection has the following characteristics:

• Healthy, vigorous and well-formed
• Near the maturity stage
• Are good producers of the desired product
• Grows in areas surrounded by a healthy stand of the same species

Very young and very old trees should not be selected because they will not produce viable seeds

Before collecting seeds it is recommended that one does a flower and fruit survey. Basically, the survey means checking out the stages of the tree in terms of flower and fruit production.

The seeds can be collected from the trees in two ways:

• Collection on the ground: this is where one collects fallen seeds. One can use plastic sheets of paper to collect clean seeds.
• Collection from the crown:

After seed collection, handling process follows. The first handling activity is extracting the seeds. Pulpy fruits such as drupe and berries might require some soaking while dry fruits such as pods and follicle might require some drying and splitting.

After extracting seeds from fruits, it is time to store them, but not all seeds can store well as they have different behaviours. The different seed behaviour includes:

1. Recalcitrant seeds: these are the types of seeds that cannot store for a long time without losing viability e.g. East African Green Heart. Once they are collected and extracted, they should be planted immediately.
2. Orthodox seeds: these are seeds that can store for a very long time without losing their viability e.g. Acacia seeds can store for up to ten years
3. Intermediate seeds are between orthodox and recalcitrant

Pre-treatment of seeds

In natural conditions, seeds of many tree species take a long time to germinate or have very low germination percentage. Tree seeds are often in the dormant stage while they await the occurrence of favourable conditions. Pre-treatment of seeds is undertaken to speed up germination time and get good germination percentages. There are various pre-treatment methods including soaking, nicking, and cracking.

Soaking seed in hot water

Soak the seed in hot water until the seeds look swollen. This is used for seeds of trees such as Calliandra, most Acacias, and Albizia.

Procedure: It is a simple procedure that involves boiling water and placing seeds inside the water. The seeds remain until they are swollen (In most cases, the seeds will be soaked overnight).

Soaking seed in cold/cool water

This method is recommended for seeds that have soft seed coats such as Sesbania, Tephrosia, Dalbergia

species, Gmelina, Gliricidia, etc. Soaking in cold water usually take 24 hours, but some species could need 2 hours.

Procedure:

• Soak the seeds in cold water which is 2 times its volume
• Remove all floating seeds
• Sow the remaining seeds at the bottom in containers in the nursery or direct sow directly in the field after

Cracking the seed shell method

This method is used for tree species with a hard coat like Melia, Podo Species, Croton megalocarpus, etc. The idea for cracking is for water to penetrate through the hard coat for easier germination. Cracking is done using a sharp knife, a stone or a cracking machine

Nicking

This is by cutting the seed coat to enable moisture to pass through to the seed. It can be done by a razor blade, sandpaper, knife or fine pliers

The point of nicking is at the place furthest from where the seed was attached to the fruit/ pod. You should be careful that you may not damage the inside of the seed.

Seeds with hard seed coat such as Acacias can be pretreated in this way

No pretreatment

Seeds such as Croton megalocarpus, Neem, Cassia spp. and Kei apple can be sown directly into the container. Fine and light seeds such as Eucalyptus, Casuarina are sown in transplant beds and later pricked out into containers. It is important that fine seed is mixed with sand and uniformly broadcast on the seedbed to avoid overcrowding that can lead to damping off (a disease in the nursery).

Planting the seeds

After applying the correct pretreatment methods, it is time to sow the seeds. The seeds can be planted into a seedbed or directly into pots. Do you know what a seedbed is?

When sowing seeds, do not sow the seed too deep in the soil; the depth of holes should depend on the size of the seeds (usually 5 mm to 1 cm). Sowing too deep is likely to prolong seed germination period or the seeds may rot. As a rough guide, cover the seed with the soil equivalent to the size of the seed.  

Cover the pots or the seedbed after sowing with dry grass and if possible make a shade.

Ideally, the sown seeds should be watered twice daily (in the morning and evening). If this is not possible then water in the evening only since most of the water at this time is taken up by the plant because there is very little evaporation at night.

You need to plan the sowing time so that the seedlings could be ready for planting out at the right time.  is important the seeds are sown in time to enable the seedlings to attain the recommended size (at least 30-45 cm in height). This should be attained before the onset of rains (April or November for most parts in Kenya).

For the propagation of many tree species, there are specific procedures for seed collection, handling, storage, and pretreatment. The availability of the information is common on many forestry websites and local organizations. Make sure you understand the seed management of the species you choose to raise in your nursery.