GERMINATING THE SEEDS

What happens when a seed germinates?

1. Unless it is still moist (B 12), it first takes in a lot of water, and becomes larger;
2. Then the cells in the growing points (C 10–12 in Manual 3) of its embryo (B 10) become very active, using chemical energy released by the breakdown of stored substances;
3. The root starts to elongate, and breaks through the seed coat;
4. The shoot enlarges, and emerges through the covering material; and
5. Seed leaves and foliage leaves expand, and the seedling begins to produce its own sugars (D 10 in Manual 4).

Is germination one of the critical stages in the life of a tree?

Yes, it is (C 40 in Manual 3), since it involves:

1. going from a resting stage to one of very active growth;
2. the delicate seedling root emerging from the seed and becoming established in the soil;
3. the young shoot growing above ground and expanding green foliage; and
4. the germinating seedling not succumbing to various common diseases or pests, and not being eaten.

Under natural conditions, there are so many hazards that most viable seeds (B 13) never become seedlings (B 4). Even in a nursery, it is still quite easy for damage and losses to occur (B 47).

Can these be avoided?

Yes, many of them can (B 3, B 50), with favourable propagation conditions and careful checking. It is a great pity to lose a lot of plants at this stage, particularly when:

1. you may have put a lot of effort into selecting, climbing, extraction and storage;
2. the seed-lot is especially valuable, for instance because:
   1. fruiting is rare (B 11);
   2. the seeds have been imported (B 24);
   3. they are to go into a provenance trial (B 21); or
   4. they come from a crossing programme (B 23).

What sort of environment is best for germinating seeds?

For seeds to germinate and grow well, their propagation conditions need to be favourable in respect of temperature, light, moisture and aeration.

Generally, they also need to be sheltered from wind and heavy rainfall (B 41), and sometimes they may require extra protection from diseases and pests (B 47).

Does the temperature really matter much in the tropics?

Average temperatures in the tropics normally permit germination to occur without supplementary heating, unlike the situation in cooler parts of the world.

However, temperature is still an important factor because:

1. overheating or drying by the sun can damage or kill germinating seeds quite easily;
2. conditions that are too cool, at higher elevations or in certain seasons, can slow germination and encourage diseases; and
3. some kinds of seeds require a diurnal fluctuation of temperature (D 11 in Manual 4) to break their dormancy (B 13, B 34).

But what can I do to alter temperature?

1. To avoid overheating, use sufficient shading (B 41) to prevent bright sunlight strongly heating the propagation medium (B 42) and the seeds;
2. For protection against cool conditions, take seed trays inside at night when you expect temperatures to drop. Alternatively, use simple polythene covers at night, or germinate the seeds in a greenhouse (C 48 in Manual 3);
3. To break seed dormancy, move seed trays from a warmer to a cooler place each evening, and back again the next morning, for the first 1–2 weeks after sowing; or try one of the other suggestions in sheet B 13.

How important is light at this early stage?

The germination and early growth of seedlings depend on substances stored in the seed. Only a little light is needed while there are no expanded leaves for photosynthesis.

Do they need any light at all?

A few species with light-sensitive seeds (B 13) will generally not germinate unless some light reaches the embryo, penetrating through the covering materials (B 43) and the seed coat.

All other kinds of trees will germinate in the dark, but do need some light as soon as they emerge, or the seedlings will become elongated and weak (C 41 in Manual 3).

So how much shading is usually needed?

For shade-bearing species (D 10 in Manual 4), moderately heavy shade at first (B 41); and
For light-demanding trees, moderate shade at first.
Then, when many seedlings in the batch are beginning to expand foliage leaves, start to reduce the shade slightly.

Small seeds contain less reserves than larger ones, and may need a little less shade.

Isn't it easy to provide seeds with moisture and air?

No, it is quite a skilled job to provide enough of both of these essentials, but not too much!
The main keys to success are:

1. using a good germination medium (B 42); and
2. watering very carefully (B 46).

How does the germination medium strike the right balance?

Because it is a special soil mix (B 42), like a very good potting mix (C 6 in Manual 3), which:

1. allows excess water to drain through it freely, but also retains moisture;
2. lets plenty of air reach the germinating seeds without drying them up; and
3. permits the roots to grow and branch easily in it, while being firm enough to support the growing seedlings.

Why do seeds have to be watered very carefully?

Because:
too much water can knock them down or wash them away, waterlog them or make them liable to damping-off or other germination diseases (B 47); but
too little moisture can dry them up before the seedling root system has become established (B 3).

Where should seeds be germinated?

In seed trays, seed beds, soil-blocks or containers (Manual 3).

Which is the best?

They each have advantages and disadvantages:
Seed trays can easily be moved around to protect the young seedlings, to reduce the amount of shade, and also when the seedlings are to be potted up or transplanted (B 45)
Seed beds may be more convenient when sowing large numbers of seeds, and usually need less frequent watering;
Soil-blocks with regular root pruning can produce planting stock with very good root systems;
Containers can be useful for large seeds, and may avoid the need to pot up the young seedlings.

And what are their disadvantages?

Seed trays can more easily dry out, and may lead to bent or tangled root systems if they are shallow, or when potting up is delayed;
Seed beds are harder to protect, and could be more liable to the rapid spread of invasive weeds, a disease or a pest;
Soil-blocks could cause wilting or uprooting if the seeds are not sown in a regular pattern, or the root pruning is done carelessly or infrequently;
Containers can be wasteful of nursery space if the germination percent is low, and may fall over and dry out.

When should seeds be sown?

For moist, non-storing seeds: sow as soon as they have been cleaned (B 32).
For dry, storable seeds: dry and keep them in good storage conditions (B 33) until a date when they will produce planting stock of the right size (B 43; and C 34 in Manual 3).

So I shouldn't just sow seeds at the start of the rainy season?

Generally no; because this is usually the time to plant seedlings out. Sowing dates often vary between 2 and 6 months before planting dates, depending how whether the seeds are slow or quick germinators, and how rapidly the young nursery trees grow to a suitable size;
but
Occasionally yes; for:

1. fruits ripening at that time whose seeds do not remain viable long (B 13); and
2. direct sowing of seeds (B 4).

What else might affect success with germination?

1. Frequent checks (B 47), careful handling (B 3) and early weeding (C 44 in Manual 3) are all important.
2. In some pines, the seedlings will not grow properly unless the germination medium is inoculated with the fungi that form ectomycorrhizas with their roots (C 31 in Manual 3).

In many other tree species, mycorrhizal inoculations can be done either in the germination medium (B 42) or at the stage that the very young seedlings are potted up or transplanted into beds (B 45).

Why is a very sheltered place important for germinating seeds?

Because shelter will tend to reduce:

1. too much air movement around the germinating seeds, tending to dry them out; and
2. the risks of damage and loss during storms or prolonged droughts.

What can I do if the nursery site is rather exposed?

1. Plant a shelter-belt just outside the nursery (C 20, C 25 in Manual 3);
2. Grow low or high hedges within the nursery (C 46); or
3. Put up a temporary shelter, for instance using mats on a wooden or bamboo framework.

For research plants, you might build a greenhouse or shadehouse (C 48), or germinate seeds in controlled environment chambers, if available.

Are there some simpler ways of providing more shelter?

1. Choosing the most sheltered part of the nursery for seed germination (C 22);
2. Planting some sizeable young trees in containers around the seed trays or seed beds;
3. Putting pieces of polythene sheeting under the shading, to keep off heavy drops of water;
4. Using temporary, movable, polythene covers, fixed so that they are unlikely to blow away;
5. Moving seed trays to a sheltered place for a while if there is a drying wind, very bright sun or heavy rain;
6. Keeping seed trays inside a building at first, next to a window, turning them round once the seedlings emerge, to correct curvature towards the light; and
7. Covering the seeds with black polythene sheeting until germination starts. Make sure that they will not get too hot, check daily and remove the covering when there are signs of germination.

Note: do not use this method for light-requiring seeds (B 13, B 34, B 40).

What about shade for the germination environments?

The aim is to:

1. provide some light, so that the germinating seedlings do not become elongated, pale and floppy;
2. have the light falling from above if possible, so that they do not curve over to one side;
3. give them indirect light, avoiding bright sunlight, except for a few minutes in small sunflecks; and
4. protect them well from heat or drought stress (C 41 in Manual 3).

Which kinds of shading are best?

Many different materials are suitable, including palm leaves, coarse grasses, bamboo slats, matting and plastic shadecloth (A 24 in Manual 1). The ordinary type of nursery shade can generally be used, but it should be particularly well made.

There is some evidence that the light quality (D 11 in Manual 4) under green foliage is less suitable for seedling growth than when the leaves in the shading are dead.

How much shade is needed?

In general, use a heavier shade than for established nursery seedlings, because it is easier to correct for too much shade than for too little.
Light-demanding species need slightly less shade than those that are shade-tolerant.

When should I start reducing the amount of shade?

This depends a great deal on the species, the season and how heavy the original shading was. The best time is generally 1–2 weeks after the seedlings start coming through, when the first leaves (or sometimes the green seed leaves) have expanded, and the young shoots are beginning to extend. The timing might need to be slightly:

earlier for light-demanding species and those with small seeds and small first leaves, since they do not have a lot of stored materials; but
later for shade-bearing species and those with large seeds and first leaves, because their greater reserves and leaf area allow more flexibility, with no need to risk reducing the shading too quickly.

How much should I reduce it?

It is usually better to decrease the shading in frequent small steps, not all at once, to a the level normal for older nursery plants of the species at that season.

Are there ways of making changing the shading easier?

1. Use a shading material of a type where some can easily be pulled out at each change;
2. Choose several layers of ‘light’ plastic shadecloth, withdrawing one at a time; or
3. Make up a varied set of portable shading covers that are easy to put over and lift off the germinating seeds.

Is there anything else that might help?

1. Keep simple records of the methods you used for each species, and the dates on which shading was changed (C 54, C 64–66 in Manual 3). Then before sowing them next time, you can check that against the number of established seedlings you obtained, and see how successful it was.
2. Do a seed germination trial (B 48), using samples from a single seed-lot grown under different shading regimes.

Aren't there some kinds of seeds that don't need any shade?

Yes. For instance, colonising species might germinate perfectly well in the open. However, when their roots are disturbed for potting up or transplanting into a bed (B 45), they might need a good deal of temporary shade, especially if their shoots are already quite large.

What other shading problems might I have?

1. Bright sunlight, low in the sky early or late in the day, reaching the seedlings. This could be corrected for instance by hanging mats.
2. The shading being dislodged, and so becoming uneven, or being blown off in a storm.
3. Branches or pieces of shading falling on to the young germinating seedlings.

Why shouldn't I sow the seeds in ordinary nursery soil?

Because they will usually germinate and thrive much better if you sow them in a specially prepared germination medium.

What are the chief features of a good medium?

One that provides:

1. sufficient moisture, but not too much (B 40);
2. good aeration, though not enough to dry out the seeds; and
3. a texture (C 23 in Manual 3) that is not compacted, allowing easy penetration of roots, but is firm enough to stop the young seedlings falling over.

What should the germination medium be made of?

A mixture of different components. There generally needs to be some:
coarse washed sand (to encourage aeration and free drainage); and sieved organic matter (for water retention, soil texture and some nutrients).

Many common materials can be used, mixed with sand in various proportions, such as:

1. weathered sawdust or partly rotted crop residues like sugar-cane or coconut fibre;
2. good loamy forest top-soil; or
3. ‘black’ soil or well-made compost.

Could I use an ordinary potting mix?

Good seed germination media are broadly similar to those for potting up older seedlings (C 6), but except for large seeds it is usually best to make a finer mix by:

1. sieving out any small stones or large gravel; and
2. avoiding adding large lumps of organic matter.

How can I find out the best mixture?

1. By enquiring from other growers (C 53), and reading nursery publications (B 52);
2. Through gaining experience yourself over a few seasons; and perhaps
3. By doing a trial to compare different seed propagation media (B 48).

Should the germination medium be rich in nutrients?

No; it should generally be less rich than a potting mixture, because:

1. unless they are very small, most seeds contain enough stored nutrients for the first weeks;
2. weeds grow even more strongly in rich soils; and
3. a lot of nutrients could discourage the formation of close associations with micro-organisms (C 30 in Manual 3).

Could I make it easier for those associations to form?

Yes, by including in the germination medium small amounts (say 2–10%) of inoculum of:

1. the fungi which form mycorrhizas (C 31) that assist for instance in the uptake of phosphorus; andlor
2. the bacteria which form nitrogen-fixing root nodules (C 32).

Where would I get the inoculum?

1. Soil from the top 5 cm from a thriving plantation or close to a mature tree of the same species, including chopped litter and rootlets;
2. Soil from containers or the top of nursery beds in which the same species has previously grown well;
3. Spores from fruiting bodies (ectomycorrhizal fungi only); or
4. Pure cultures of selected micro-organisms (B 52).

Won't adding those things make the seeds more likely to rot?

Definitely not, when pure cultures are used;
Generally no, because these are beneficial micro-organisms; but
Occasionally yes, if others that cause disease are also present (B 47).

Is it also possible to inoculate the seedlings later on?

Yes, small quantities of the relevant inoculum can be well mixed either into:

1. the potting medium or the topsoil of the nursery bed when transplanting (B 45); or
2. the soil when planting (Manual 5).

A few species like the ectomycorrhizal pines need the inoculum in the germination medium, or they grow very poorly.

What can seed trays be made of:

These are often made up from pieces of thin wood. Plastic seed trays of various kinds are also available (B 52), or they can be cut out of used containers and holes punched in them.

How big should they be?

The depth is the key measurement to choose, because:
If they are too shallow, they may restrict the roots and dry out rapidly; but
When they are too deep, trays may be heavy to carry and tend to break soon.

So what size might be convenient?

Depth: about 10–12 cm (minimum 6 cm; maximum 15 cm);
Length: around 40–50 cm; and
Width: about 30–40 cm.

Before making or ordering seed trays, think about choosing a size that will fit well on nursery beds, and on trolleys or benching if they are used.

What about sowing in nursery beds?

Prepare new seed beds of a size that is convenient to the nursery layout (C 22), making sure that they will have good drainage, and then add the germination medium as a layer 5–10 cm thick on the top.
Renew existing beds by removing weeds (C 44), levelling and adding some new medium.

Are there some other things to watch out for?

1. Avoid putting weed seeds or resting stages of pests into the germination medium;
2. Check that toxic chemicals cannot get into the medium or the water supply (C 24);
3. Leave enough space above the medium in seed trays to cover the seeds suitably (B 43) and still permit watering (B 46).

When should I sow the seeds?

For seeds that can be stored (B 33): about 2–6 months before they will be planted, so that by then they will have germinated and reached a suitable size; but
For seeds that cannot be stored: as soon as they have been collected and cleaned (B 31–32).

What needs doing beforehand?

Before actually sowing the seeds:

1. read up about seed handling and germination (B 30–33, B 40–48, B 52);
2. do any necessary pre-sowing treatments (B 34), including slow warming up of unopened containers of seeds stored cold;
3. decide whether to sow in seed trays or beds, or in containers or soil-blocks (B 40);
4. prepare a shady, sheltered seed propagation environment (B 41), and mix up a suitable germination medium (B 42); and
5. get out labels, pencil, record sheets (C 64–65 in Manual 3) and anything else you will need.

How should I start, if I am sowing in seed trays?

Put the germination medium into the trays, and then firm it down gently with a flat board, so that the surface is smooth and even, and comes to around these distances below the top:

1 cm - for seeds less than 2 mm diameter;
1.5 cm - for seeds of 2–5 mm diameter;
2 cm - for seeds more than 5 mm across.

And what about seed beds?

Cultivate the surface of the bed, put 5–10 cm of germination medium on the top, rake it level and firm it down, but not too hard.

How should the seeds themselves be sown?

Smaller seeds: scatter them thinly and evenly over the surface of the germination medium. With practice, one can avoid having many seeds touching each other, which could:

1. encourage damping-off disease (B 47);
2. leave inadequate growing space for the young seedlings; and
3. make them difficult to separate when potting up or transplanting (B 45).

Seeds large enough to pick up: it may be easier to sow these individually, spaced out:

1. at about 2–3 times their diameter in a seed tray or bed;
2. one to three in a container, depending on the expected germination percent (B 48); or
3. in regular lines in a soil-block bed, so that root-pruning will be easy to do (C 4 in Manual 3).

What spacing might be suitable for these larger seeds?

No closer than 1 cm to each other, and often 5–25 cm apart, to allow each plant enough room. See C 63 in Manual 3 for calculations about the space needed.

Why do seeds need covering?

1. So that they are within or close to the favourable environment of the germination medium;
2. To protect them from being overheated and dried out, or washed and blown about;
3. To hold them down sufficiently for the emerging root to grow into the soil rather than push the seed about; and
4. To make them less likely to be seen by birds or mice.

What sorts of covering would not be suitable?

Very fine soil particles, which could impede free drainage, holding water near the surface, which encourages damping-off disease (B 47); or
Large particles or lumps of earth, which might restrict the emergence of the young shoots.

Which kind of covering is best?

Although this can vary from one species to another, one can often use:

1. coarse sand or fine gravel (2–4 mm diameter), or a mixture of both; or
2. the germination mixture.

And how should it be put on?

Smaller seeds: sieve the covering material over them until they are covered uniformly. The covering should come up to about 7–8 mm below the top edge of seed trays when it has been gently firmed down.

Larger seeds: these can either be:

1. put or pushed into a small hole, which is then closed with the covering material; or
2. placed on the surface, and then the covering added and firmed down.

How thick a covering would that be?

Here is a rough guide, which you may need to adapt for particular species:
Seeds less than 2 mm diameter: just enough to cover them;
Seeds 2–5 mm across: cover with about 4 mm; and
Seeds bigger than 5 mm: use about the same depth as the seed diameter.

What about seeds that are light-requiring?

In such cases (B 13, B 34), the covering should not be too thick, and should preferably be of a light colour, allowing light to penetrate further.

How about watering seeds?

Method 1: Do NOT water now if the medium is moist enough, and the seeds already contain enough water for germination, either naturally (B 13) or from soaking (B 34).
Method 2: Water well with fine droplets (B 46) if the seeds are dry and/or the germination medium is not moist enough.

Afterwards, check regularly (B 47), and water sparingly as needed (B 46). With seed trays, you might consider restricting their drying by covering them loosely with clear or white polythene sheeting until the seedlings emerge.

Are there other ways of covering seeds?

Some growers cover seed trays with thick newspapers or black polythene and don't water again until the seeds come through. Two problems that can happen with this technique are:

1. if the trays are not checked daily, early germinating seedlings become very elongated in the near darkness, or bend over towards light coming in from the side; and
2. diseases might be encouraged if the germination conditions are humid and still (B 47).

What other difficulties might I have?

1. Small seeds, or those with wings, blowing about on a windy day before you can cover them.
2. Being unsure, if no seedlings come up, whether:
   1. the seeds are dormant (B 13);
   2. they take a long time to germinate;
   3. all of them have been eaten (B 47);
   4. they have rotted in a medium that was too damp or cool (B 42);
   5. none of them ever contained viable embryos (B 13); or
   6. they have lost viability since they were collected.

These and other problems are covered more fully in sheets B 3, B 50 and B 52.

And what are the signs of good germination?

Plenty of well-spaced, healthy seedlings emerging.
Seedlings often come through with the shoot bent over like a hook, which in the light soon straightens out.

How about the young leaves?

The seed leaves may remain below ground, or emerge and turn green. Often they contain storage materials.
The first foliage leaves usually look different from those produced later on, so make sure that an unfamiliar species can be distinguished from a weed.

What are wildings?

Seedlings that are collected from:

1. underneath or near the seed tree;
2. in a place where they were buried by animals or deposited in their droppings; or
3. at the edge of water, for a few species in which the fruits float.

Where might I find the droppings?

Some birds and climbing mammals have perches under which wildings might be found. Bats may pass droppings while on the wing, or at their day-time roosts in caves or hollow trees.

How about seeds that have already germinated?

Many wildings have to be dug out of the ground, but sometimes they can just be picked up, because:

1. the seeds have only recently germinated, and are lying in the leaf litter or within pieces of rotting fruit (as in cocoa); or occasionally
2. they have developed into seedlings before they were shed from the tree, as in some mangroves, such as Rhizophora (B 12).

Collecting wildings and soil.

What are the advantages of using them?

1. They have already reached the germination stage or beyond, without one having to collect fruits or extract the seeds;
2. They may already be forming close associations with local micro-organisms (C 30–32 in Manual 3), and inocula will come with them in the soil around their root systems; and
3. In some species with dormant seeds (B 13), such as Ricinodendron heudelottii, using wildings in which the dormancy has been broken by natural agencies may be the easiest way of overcoming the problems of slow germination caused by the stony inner fruit wall, and also of minimising psyllid attack.

And how about their disadvantages?

1. Wildings may be difficult to find, or only a few may be collected;
2. They may not be available at the appropriate time;
3. One might be growing young trees without choosing which parent trees to use (B 22); or
4. If they are collected far from the nursery, they might suffer more damage and stress in transit than seeds germinated in the nursery.

How should they be handled?

1. By carefully digging up those that have rooted into the ground, if possible keeping a firm root ball that will protect the root system;
2. By handling wildings that are in loose soil, and recently germinated seeds, with great care, avoiding breaking the roots.

Put them in moist polythene bags within boxes to minimise crushing, and keep them out of the sun and wind. Transport them as soon as possible, but without bumping them about.

Where should they be taken?

Usually to the nursery, where they can be:

1. potted up or transplanted into beds at once (B 45);
2. grown at first in very shady conditions (B 41); and then
3. accustomed gradually to the ordinary nursery regimes; but

Sometimes directly to the planting site, where wildings might establish successfully if:

1. they were neither too small nor too large;
2. they were planted when the rains had started; and
3. there was enough overhead shade at the planting site.

Which species can be planted directly?

Trials at Kavwaya in Congo showed for instance that it was fairly straightforward to plant wildings of Gaetnera paniculata, Millettia laurentii and Ricinodendron heudelottii directly into farmers' fields after cassava and groundnuts had been planted.

How big can wildings be, to stand up to being moved?

Ideally, they need to be less than about 50 cm tall. However, if most of the wildings available are larger, and the root systems have been considerably disturbed, you might try:

1. putting them in pots and keeping them in poly-propagators (A 31 in Manual 1) for 1–2 weeks, and then weaning and hardening them like rooted cuttings (A 54);
2. trimming off parts of the larger leaves (A 41; C 47 in Manual 3); or
3. cutting the shoots back, in those species that can resprout easily from basal buds or from coppice shoots (A 21), and perhaps propagating the tops as cuttings (A 42).

Is there anything special about potting up very young seedlings?

The general principles are the same whenever nursery root systems are disturbed (C 42 in Manual 3), but extra care is needed when the plants are very small (B 40; C 40).

Why should they be disturbed so young, anyway?

Quite often they do need to be moved, because the small seedlings are:

1. in seed trays that cannot continue to support the formation of good root systems;
2. growing too close to each other; or alternatively
3. at too wide a spacing for economical use of the growing space; but

Sometimes digging them up can be avoided, since the young seedlings:

1. were sown in containers that are large enough for their entire stay in the nursery (C 6);
2. can stay in the seed bed until they are used as striplings or stumps (C 47); or
3. are spaced regularly in soil-blocks, where they will be regularly root pruned (B 40; C 4).

But isn't the best kind of root system one with a strong taproot?

No, only for the initial stage of germination, when it makes the vital link between seed and soil.
After that, taproots are important in just a few tree species, and for direct sowing (B 4).

In general, long seedling roots need to be discouraged in nursery plants, so as to produce a bushy, compact root system (C 34, C 47) that can be successfully planted (Manual 5).

How can the long roots be checked?

1. By actually pruning the ends of the roots off (C 4);
2. Through moving containers about from time to time, or setting them where they cannot ‘root through’ into the ground (C 6); or
3. By using root-trainers.

When should seedlings be potted up?

The best time is usually at a fairly early stage, when:

1. they have expanded a few small green leaves, but the shoots are not yet growing very fast; and
2. the root systems have started to branch, but have not yet become tangled together.

Do this work early in the morning, or in the late afternoon.

How should it be done?

1. Water the young seedlings well the night beforehand (B 46);
2. Prepare a shady working place (C 22), and fill (or for larger root systems partly fill) the containers with a suitable potting mix (C 6, C 42);
3. Start at one side of the seed tray or seed bed, and use a small, flat, pointed piece of wood to lift out a seedling with as little disturbance as possible (or if necessary a small group of seedlings);
4. Make a hole in the potting mix that is big enough to take the root system without bending it over, insert a seedling (holding its leaves rather than roots), and carefully firm it in. With larger root systems, carefully fill in soil around them, and firm it down gently.

What differences are there when transplanting into a nursery bed?

1. It may be somewhat harder to reach all parts of a transplant bed (C 26);
2. However, it can be rather easier to transplant larger root systems;
3. Having adequate shelter and shading (B 3, B 41) is more critical, since the young transplants cannot be moved to protect them from extremes.

When should I water?

Firstly, the potting medium should be moist or the transplant bed pre-watered if necessary.
Then (C 46), there are three alternatives:

1. waiting until watering is needed, or it rains;
2. ‘watering in’ the containers or beds the same evening as the transplanting; or
3. pouring water into the hole as the transplanting is done.

Are there some general guide-lines?

1. Transplanting is a key stage in the life of young trees (C 40), when they can very easily be damaged or killed;
2. It is well worthwhile putting effort into training staff and workers (C 52), or family members, in careful handling of the young trees and the avoidance of unnecessary stress.
3. Within 1–2 weeks, the young trees will usually have become well established in their new positions, and be much less liable to damage.

Is there anything special about watering seeds and very young seedlings?

Yes, there are several important points, in addition to those described for watering older plants in containers and nursery beds (C 43 in Manual 3).
During germination, the new seedlings:

1. lack a well-developed root system (C 11);
2. have a rapidly increasing liability to water loss from the shoots (C 41);
3. are particularly susceptible to damage by diseases or pests (B 47).

What does this add up to in practical terms?

That it is very easy to give too much water, or too little.

So how can I avoid those extremes?

Dry seeds (B 12, B 33): by making sure that they can take up enough water to germinate (B 34), but do not then remain in waterlogged conditions; and
Moist seeds: by washing them free from remains of the fleshy fruits (B 32), but neither leaving them to soak for too long, nor dry out.

And then by using a good germination medium?

Yes, that's right - one that provides enough aeration as well as moisture (B 42–43). In addition, adequate shading (B 41) reduces the need for frequent watering.

Do I need to water seeds straight after sowing?

Choose Method 1 or 2 (B 43), depending on the circumstances.

Should I water the seeds again before they come up?

Generally no; as there will be little evaporation from them, and so the germination medium may remain moist, except perhaps on the surface; but
Sometimes yes; if wind or high temperatures are drying out the medium more rapidly.

What about watering when the seedlings are just coming through?

This is the most difficult stage to judge correctly. Until the medium is beginning to get a little dry, it is usually best to avoid watering, because:

1. the young shoots are unlikely to be losing much water yet, as the small holes in the leaf surface (C 12 in Manual 3) generally remain closed until the young leaves have unfurled and expanded considerably;
2. the root system generally starts to grow and branch before the shoots emerge, so the water balance is maintained (C 13);
3. water around the root collar encourages the development and spread of damping-off disease (B 47); and
4. extra moisture might also attract insect pests, which at this stage may destroy (instead of just damage) the plants.

How can I check whether the medium is starting to get a bit dry?

1. Through noting that its surface is becoming a paler colour;
2. By checking once or twice each day, making a small hole with your finger to test it;
3. From records of when rain fell, if germination is in the open.

On the other hand, avoid waiting until seedlings are beginning to wilt.

When watering is needed, how should it be done?

Preferably:

1. early in the morning;
2. applying moderate quantities of water with a watering can that produces fine drops;
3. evenly over the whole surface of the seed tray or seed bed.

Start and finish the watering to one side of the seed bed or tray, allowing only a steady stream of droplets to fall on the germinating seeds.

What if I do not have access to a watering can?

You could make a lot of small, regularly spaced holes in the bottom of a tin, and then dip this repeatedly into a bucket, using it to sprinkle water evenly.
Another way is to stand the trays briefly in shallow water, so that water enters from below, and then let the excess drain off (C 43).

And what should I do as the shoots expand?

The frequency of watering, and the amounts given, both need to increase as the leaf area (C 12) becomes larger.

What about when the root systems are disturbed?

The time when young seedlings are first potted or transplanted into beds (B 45) is a second key stage in their development. Stress can be minimised by:

1. watering them well the day before moving them;
2. putting them into a fairly moist medium;
3. careful handling (B 47); and
4. extra shading for the first week or so (B 41).

But supposing some of them do start to wilt?

Take action as soon as you see this beginning to happen, or a lot of your trees might be damaged or die. You could for instance:

1. put up extra shading;
2. cover affected plants loosely with polythene bags or sheeting;
3. place shallow pans of water near the seed bed to increase local air humidity, changing the water and refilling as needed; or
4. move seed trays or containers temporarily to a very shady, moist place, inside a building (B 41) or into a poly-propagator (A 31 in Manual 1).

Note: do NOT water them if the soil is still moist! The aim is to reduce water loss from the shoots until the uptake of water by the roots can catch up (C 13 in Manual 3).

Does it matter how clean the water is?

Yes it does, if the water contains a lot of nutrients, dissolved pollutants that are toxic to plants (C 24), or resting stages of micro-organisms causing disease (B 47); but

No, it may not, if it is mixed with fine sediments, since these can usually be removed by:

1. leaving the sediment to settle for 1–4 days, and then taking water carefully from above, without disturbing the mud at the bottom; or
2. passing the small quantities needed through a simple filter.

What could that be made of?

You could for example put a layer of cloth or newspapers into a sieve, cover that with a thick layer of fine sand, and set it on a bucket. Pour on water a little at a time - the first that comes through may be a little dirty, but then it should become much cleaner.

Are there other problems I might run into?

See sheets B 3 and B 50 for this.

What sort of checks are needed during germination?

Those described in sheets C 40 and C 66 in Manual 3, but done more frequently, so that:
‘daily’ checks might occur 2–3 times each day; and
‘weekly’ checks could happen every two or three days.

Isn't it a waste of time to do it so often?

No, since:

1. it need only take a few minutes;
2. germination is a key stage when young trees are particularly vulnerable to damage;
3. trouble can then be spotted early, before much harm has been done; and so
4. you may well avoid losing large numbers of germinating seeds and young seedlings.

What do I need to look for?

Any signs of poor growth or unusual colour, or seedlings falling over.
Any problem with the shelter, shading or watering.
For further details, see sheets B 3 and B 50.

Which kinds of protection do very young trees need?

1. Shelter and shading (B 41), to limit the extent of climatic stress (C 41);
2. Fencing or close-grown hedges, to keep out larger animals (C 46);
3. Measures to deal with any pests that threaten them;
4. Careful handling and watering (C 45–46), to reduce the risk of diseases attacking them; and
5. Frequent weeding (C 44), to minimise root and shoot competition and extra disturbance later on.

How can I keep off pests?

By following the advice in sheets B 30 and C 45, paying particular attention to:

1. regular checking for signs of insect presence or build-up, particularly of kinds such as aphids and psyllids which can multiply quickly, and leaf-eating kinds that will grow big;
2. removing insect eggs, caterpillars or resting stages, for instance from the undersides of young leaves in the germination area and from other plants in the nursery; or
3. covering germinating seedlings with wire mesh to prevent mice from digging them up or breaking them off.

What kind of diseases cause most problems?

The commonest attack is from damping-off disease. The symptoms of this are:

1. a discolouration of the young stems just above ground level;
2. seedlings falling over; and
3. death of the entire root system, and then of the shoot.

Is there anything I can do if my seedlings are attacked?

1. Carefully remove all affected seedlings, and bury or burn them;
2. Reduce the air humidity and soil moisture a little by slightly decreasing:
   1. the level of shading (B 41);
   2. the amounts and frequency of watering (B 43, B 46); or
   3. the amount of water added.

It is sometimes possible to save important seedlings by cutting above the infected part and rooting the top of the shoot as a leafy cutting (B 2; A 4, A 40 in Manual 1).

Can I prevent damping-off happening and spreading?

As well as considering points (B 1–3), you could:

1. sow seeds more thinly, so that the root collars of seedlings do not stay wet so long, and are less likely to infect each other;
2. water early in the morning, rather than at night;
3. water from below (B 46) instead of above;
4. sterilise the germination medium (C 44–45 in Manual 3); and if necessary
5. treat the seeds or the medium with a fungicide such as propamocarb or benomyl.

Are there other diseases that might give problems?

See sheet B 24 and B 30–34 for avoiding or reducing problems with seeds before sowing, and C 40 and C 45 in Manual 3 for the protection of older seedlings.

Anyway, what does a thriving young seedling look like?

Some features are easy to see, such as the:

1. shoot extending fairly rapidly;
2. leaves becoming a fairly dark green; and
3. plant free from obvious pests or disease;

But other things may be hidden, such as the:

4. roots growing and branching freely through the germination medium;
5. genetic origin being appropriate for the locality (B 3, B 20), and not inbred (B 22); and in some pines, for example
6. inoculation with a suitable ectomycorrhizal fungus having occurred (B 42).

What else is important with a larger nursery?

1. Learning how to provide favourable seed propagation conditions (B 40) for each different species;
2. Discovering the people who have ‘green fingers’, treating the young seedlings gently and successfully; and
3. Watching out for problems at weekends and during holidays.

Why should one bother about doing germination tests?

Often they are not needed; but
Sometimes they can be very useful, for instance:

1. to check whether older seed-lots are still viable (B 13);
2. to calculate the germination percent in order to know how many seeds to use, and how thickly to sow (C 63 in Manual 3); and so
3. avoiding having the seedlings either:
   1. growing too close together (B 43); or
   2. with large gaps between them, wasting a lot of seed propagation space and germination medium.

But won't the tests themselves often be a waste of seeds and time?

There are certainly many occasions when germination tests are not appropriate, for example:

1. when the seeds are of a type which cannot be stored while testing (B 13);
2. if no suitable storage facilities are available for storable seeds (B 33);
3. if there are only a few seeds of the species available, or they are particularly valuable; or
4. when the people who know how to do valid seed tests are too busy with other work.

Can't I get a rough idea by just sowing the seeds and seeing what happens?

Yes; sometimes that's the best thing to do; but

The drawbacks are that:
if they come up, the spacing of the young seedlings may be unsuitable;
if they don't, you may not know whether the seeds were empty, dead or dormant (B 13), or if perhaps the seed propagation conditions were unfavourable (B 40–43).

How does one set up a proper germination test?

There are several kinds of test (B 33), including:

1. sowing known numbers of seeds in nursery conditions (in seed trays, pots or beds) and recording how many seedlings come up;
2. doing the same on moist filter paper in petri dishes in controlled environments, and seeing how many germinate;
3. cutting sample seeds across and counting how many have firm, whitish contents; or
4. doing the tetrazolium test.

What are the most important things about seed testing?

1. Taking an unbiased sample of the seeds for the test, by mixing the entire seed-lot well, and then withdrawing small samples from different parts of the pile or bag;
2. Using enough replicates of each batch to be tested - at least 5 and preferably 10 sets of seeds;
3. Sowing in reasonably uniform conditions, preferably standardised so that closer comparisons can then be made with previous tests.

How many seeds would be needed altogether?

With a large seed-lot, one could for instance use 10 replicates with 100 seeds in each, making 1000 seeds in all.
With a smaller seed-lot, one might perhaps test 5 replicates of 30 seeds, using 150 seeds.

What sort of controlled environments are needed for more accurate seed testing?

1. The simplest type is like a small oven that can be set to maintain say 30°C.
2. An improved version is operated in an air-conditioned room, allowing temperatures down to about 20°C to be maintained. It could have two thermostats and a time-clock to give different day and night temperatures, and a low-wattage light for light-sensitive seeds (B 13, B 34).
3. Seed-testing stations have several large germination chambers, usually pre-set to give standard conditions. They may have built-in refrigeration units as well as heaters, so that they can operate at a wide range of temperatures. Pollen germination tests (B 23) can also be done.

Don't the seeds dry up easily during the test?

Small seeds can be sown on filter paper in petri dishes with lids, using just enough water for the papers to remain moist after dry seeds have absorbed water (B 34).
Larger seeds can be sown in shallow containers and put inside polythene bags.
If watering is needed, it should be done with water that has been kept at the same temperatures.

How long should a germination test continue?

Ideally until several weeks after the last seeds germinated. Sometimes, however, it may be more convenient to fix a shorter period, and then perhaps cut the non-germinating seeds across to assess whether they were viable or not.

What about the tetrazolium test?

This is an alternative to germination testing, which is based on a colour reaction on the surface of the cut seed. The chemical name of the substance used is 2,3,5- Triphenyltetrazolium chloride (xxxx in B 52). Fully viable embryos usually stain red, doubtful seeds pinkish red and dead seeds a paler pink. (Is this right?) The number of empty seeds can also be counted with this technique.

Supposing I wanted to do an experiment about seed germination?

In that case there would be two or more treatments applied, each with say 150 to 1000 seeds divided into 5–10 replicates.

What sort of treatments might be relevant?

Many different kinds, for example involving:

1. comparing germination of the same fruit collection with different seed handling methods (B 31–32);
2. working out drying regimes and storage conditions (B 33) in which the seeds will remain viable for a longer time;
3. identifying seed dormancy (B 13) and studying how to break it (B 34).

Another kind of experiment might compare different methods of testing seed germination.

Can you give some guide-lines?

1. Try and keep all the conditions similar except the points being studied (C 15 in Manual 3);
2. Keep the experiment simple, preferably with only 2–4 treatments, but use plenty of replicates and seeds; and
3. If you have a seed problem (B 3), you might make more rapid progress by combining:
   1. asking whether other growers have overcome it (B 24), and looking for published information on the subject (B 52); and
   2. doing a simple preliminary trial while waiting for larger supplies of seed.

Are there other kinds of experiments using seeds?

Yes, there are several kinds, such as:

1. starting an experiment with young trees in pots (C 15 in Manual 3);
2. growing trees in standardised conditions for field research (C 7);
3. raising the seeds from genetic selections (B 20–23) in uniform environments, so that differences between provenances, progenies or hybrids are not confounded with dissimilar early growing environments.

Does ‘confounded’ mean ‘mixed up with’?

Yes, that's right - so that different causes cannot be separated. There are a number of reasons why it is easy to draw conclusions that are not valid from experiments (C 67-B (2), and C 67-O in Manual 4).

Apparent ‘treatment’ effects could also arise for example from:

1. early germinators tending to outgrow and shade those which start to grow later;
2. seedlings that germinated in shadier places being likely to be taller, and to have different leaf structure and less stored materials than others that grew in a sunnier spot; or
3. some of the seedlings having been affected by drought stress or nutrient differences.

So how can one avoid that kind of thing happening?

Partly by keeping the growing conditions as uniform as possible (C 48 in Manual 3);

Partly by ‘grading’ (B 45 in Manual 1) and randomising (C 15) the experimental seedlings; and

Partly by using experimental layouts such as randomised Blocks to make sure that each part of a variable experimental site contains all the treatments (D 55 in Manual 4).