Successful Sprouting

Storage

Seed from most tree species will germinate satisfactorily if washed, dried and kept in a cool, dry place through the winter and then sown in spring. e.g. Abies, Acacia, Alder, Cedar, Cryptomeria, Larch, Mulberry, Pine, Pomegranate, Sequoia, Sophora, Elm, & Zelkova. The easiest of these could be sown in weed free, prepared beds outdoors. For more valuable or tricky species the extra effort of preparing germination boxes on a windowsill, in a frame or greenhouse is worthwhile.

Some seed responds in unexpected ways. Hornbeam is reputed to be easy from seed, but purchased batches, from different sources, failed to germinate for a number of years for me. Seed collected fresh, while still slightly green in early October and stratified over winter, achieved almost 100% germination in spring. The rare Carpinus turkzaninowii (Rock Hornbeam) achieved 100% germination, straight from the packet, last spring. It was so successful that it became a chore pricking them out! If you only ever try one packet and it fails, don't blame yourself, it could be that it wasn't viable.

Many seeds demand stratification or exposure to low temperatures or frost to break their dormancy. See Stratification techniques and the table below.

Preparation

Some seeds benefit from preparation before sowing. Hard shelled seed like Walnut, Olive, Ginkgo etc germinate faster if the shell or seed coat is carefully cracked, filed or chipped. This eases penetration of moisture, inducing the seed to break dormancy. A nut-cracker, file or sharp knife should be employed as appropriate. Smaller seed with a hard coat may be rubbed with sandpaper. Great care must be taken that only the coat is fractured, as any damage to the embryo is likely to cause rotting.

For seed to germinate it should be sown at the correct time of year for the species and given the right conditions.

Cycad Seed sent to me from Florida

Remove the fleshy coat of seeds in berries - take care with Cycads though, the seed coat is poisonous!

Hard shelled seeds germinate faster if the shell or seed coat is carefully cut through or filed.

Cycad seedling 1 year later

Stratification

Mix the seed with sharp sand in layers in a plant pot. Cover the pot to exclude animals and place in the most exposed position in the garden to allow frost and rain to act on the seed.

Stratification in a refrigerator

Mix seed with a small amount of damp sand, vermiculite or sphagnum moss and place in labelled polythene bags. Seal and place in the salad drawer of the fridge. Most seed of deciduous trees requiring stratification will germinate given 0-1°C (33-34°F) for 6 to 8 weeks. Conifers generally need only three weeks. Check occasionally for signs of germination. Some begin growth in the fridge and would soon become drawn and die through lack of light. Some seed will not germinate while cold and only begin the process after the temperature rises. A useful strategy, if the procedure is unknown, is to sow some of the stratified seed after 2, 4, 6, 8, 10 and 12 weeks. In this way some of the seed is likely to receive the correct amount of cold and by keeping a record you can improve future successes.

Stratification Requirements

Rigid adherence to the times in the table is unnecessary. Good results are often obtained by leaving outdoors for nature to take its course.

Suggested Species

Most species of tree may be raised from seed. For bonsai it is best to concentrate on those that grow rapidly and have some desirable characteristics such as small leaf size, good flowers, unusual bark, autumn leaf colour etc. If not sowing seed that you have collected yourself, order during autumn or winter, soon after the seed catalogue for the year becomes available. The sowing season will not then be missed. Some seed has a limited viability and, if not sown in the first spring, may fail to germinate completely.

Easy (no stratification required) and fast growing:- Alnus, Carpinus turkzaninowii, Cryptomeria, Juniperus, Larix, Morus, Pinus, Punica, Sophora, Ulmus, Zelkova.

Strong germination from Larch sown three weeks earlier - straight from the packet, i.e. no stratification.

Easy with stratification :- Acer, Crataegus (but often takes a couple of years), Cupressus, Cydonia, Fagus, Malus, Quercus.

Easy but requiring some care not to over or under water at seedling stage:- Abies, Cedrus.

Tricky or lower germination rate, but well worth trying:- Ginkgo, Olea, Metasequioa, Pistacea, Pseudolarix, Rhododendron, Sequoia, Sequoiadendron, Taxus.

Seed Compost

Either use a commercial seed compost or make up your own. I always make my own and get good results.

The particle size for all constituents should be fine to medium, about 1mm to 3mm. Sieve and discard all particles too large or too small. The finest particles can be used for garden beds and coarse stuff for potting mature trees. My recipe for home made seed compost is as follows:-

25% Sharp sand - Bought bagged from garden centres.

50% Fibrous loam - I use turves from lawn edges, rotted down in a stack for at least a year. Sterilise with steam over a boiling pan.

25% Organic matter - Either peat substitute, composted bark, leaf- mould, pine mould, chopped sphagnum moss or peat. May also be sterilised.

Sowing

Use new seed trays, half pots etc or scrub them using a sterilant, such as Jeyes Fluid at the manufacturers recommended strength, if they have been used before. Have enough seed compost ready. Three-quarter fill the containers with compost and level without compressing.

Small seed e.g. Rhododendron may be mixed with fine sand and evenly distributed on the surface of the compost.

Many tree seeds are large enough to handle easily. These should be sown evenly on the surface of the compost with space to develop the first set of leaves. The larger the seed, the larger the space required between them.

Seed such as beech, hornbeam and zelkova should be sown with the point downward to encourage a straight stem.

Cover the seed with a depth of fine compost equal to the depth of the seed.

Growing under glass at the start is the way to achieve the best possible germination rate. If the seed that you are sowing is plentiful and easily grown outdoors, it may be sown in a seed bed prepared in the garden. Choose a sheltered spot that receives some sun and clear it completely of any perennial weeds. Improve and lighten the soil texture with the addition of grit, sharp sand, and humus such as compost, bark mulch, leaf mould or peat. The seed is then sown, either in autumn or spring, according to the species. Protection from rodent attack is advisable. Wire mesh encircling the bed is one way. Once germination occurs, other pests may be troublesome - slugs, aphids etc.

Care

After the seed is sown, water by placing the tray in shallow water until it’s drawn up to the surface. (Wait for the soil colour to darken.) The first watering can include a copper based fungicide to prevent damping off. This is a fungal disease that sometimes causes failure just after germination, while the seedlings are still very soft and prone to attack. Watering again is not necessary for a while, but check every few days to make sure that the compost is not drying out. It helps to cover with a sheet of glass and lay newspaper on top. This prevents undue evaporation and maintains a humid atmosphere. Check regularly to ensure that both the paper and glass are removed as soon as germination begins. If it is not, the seedlings become drawn and soft through lack of light and are more likely to succumb to damping off.

Many plants, such as these Hostas for example, readily cross pollinate and may produce attractive variants. Dwarf ones could produce a superdwarf, if you're really lucky! I've selected one from this whole tray full that warrants keeping. It has a narrower, lance-shaped leaf and has the potential to be more attractive than its parent.

Watering

After germination a closer watch must be kept, allowing the surface of the soil to just dry before watering with a fine rose. The seedlings should never be allowed to dry until they wilt, they rarely survive this.

Ventilation

After the first seeds germinate, too close an atmosphere will encourage fungal diseases and should be avoided.

Light

The sheet of paper over the glass prevents overheating when the sun shines. Once the glass and paper are removed, place the tray out of direct sun, but in good light, for the first week or two. When the first true leaves have developed, you should accustom them to full sun. Do this by gradually reducing the shading or moving them where more and more sun will be received. Only provide slight shade for those that require it, e.g. most Acer's. Then gradually harden off outdoors, once any danger of frost has passed. A cold frame is useful for this, but it may just as easily be achieved by placing outdoors for longer periods each day, for a week, and then leaving them out.

Feeding

Seedlings grow for a short period by using up stored goodness in the seed leaves (those initially enclosed in the seed pod). After this, they develop their first true leaves. The young roots are very tender and feeding, if any, must be with a weak solution, after the seed leaves have withered. I prefer to transplant (prick out) and wait a couple of weeks before feeding.

Transplanting

Most of the seedlings are best pricked out after the first true leaves have developed. Allow the compost to dry slightly and then carefully break up the soil so that the tender roots suffer as little damage as possible. Handle the seedlings gently, by holding a leaf, not the stem. Fill each pot about three quarters full with a fairly coarse mix and mound up the centre. To ensure good radial root development from the start, you should carefully arrange the young roots, so that they are spread evenly around the seedling. If it has a dominant taproot, trim this to encourage side roots. Trickle dry soil over the roots, until it is at the same level on the seedling's stem as it was in the seed flat. Don't compress the soil, but water it thoroughly. This ensures that soil is in contact with all the young roots. Keep the seedlings semi-shaded in a cool greenhouse or frame for a week or two and then gradually harden them off.

Starting bonsai from seed is slow but one of the most satisfying of the horticultural skills that you can master. Anyone can do it, but if you want something to begin working on buy a few nursery trees to keep you going, while you wait for your seedlings to mature.

A Special Technique - Seedling Cuttings

Seedling cuttings are made to produce young plants with a better spread of roots than would naturally occur. Once the first true leaves appear, the seedlings are removed from the growing medium and the roots washed. They are decapitated at just above the root level, with a scalpel or razor blade. Stand them briefly in liquid rooting hormone and then replant in the damp growing medium. Mist spray regularly and keep out of direct sun, until new roots are formed. Most species will root rapidly and develop stronger radial root systems than if they had been left to develop naturally. This technique is used particularly with pine seedlings in Japan, but I also "discovered" the technique myself, prior to reading about it, when sciarid fly grubs ate all the roots from a pan of Pinus densiflora seedlings. I didn't use any rooting hormone, just forlornly placed the rootless pines in sharp sand and to my surprise they all rooted and grew on strongly.

Failure to germinate

Several reasons may contribute to this. The seed may be old and slow to break dormancy. The pre-sowing treatment may not have been at the correct temperature. In the worst scenario the seed may not be viable at all and the best plantsman in the world cannot get unviable seed to germinate. Even when the best care has been taken some batches of seed fail to grow. The important thing is not to give up hope. Check that the trays or pots are labelled adequately, with the name and date, and then put them outdoors until the following spring. Frequently I have given up on a seed flat, placed it in a corner of the garden and then happened to glance at it a year, or even two years later, and there are the tell-tale thrusting growths, indicating a surprise result. e.g. Acer's, Hornbeam's, Gleditschia.

Speeding the process up

Getting maximum healthy growth is the aim at the start. Always water as soon as the compost begins to dry out and begin feeding, with a weak fertiliser initially, a fortnight after pricking out. Gradually increase the strength to the same as you use for adult trees. The combination of sun, water and food will encourage healthy growth and more rapid ramification. A good number of seedlings allows you to select ones suited to various styles and sizes of tree at an early stage. The trimming, wiring and training can thus be implemented from the start. This is especially useful for mame.

If you wish to develop a thick trunk more rapidly, plant out one year old saplings in a bed, or any space in the garden for that matter. Remove any weeds and prepare the ground with the addition of grit to improve drainage and compost for faster growth.
Keep well watered in dry periods and fertilise regularly during the growing season. The tree will put on much more girth than if it had been left in a pot.

Pests such as slugs and rabbits can easily kill saplings at this stage so take any precautions that you deem necessary. I have found that young Acers, Mulberries and Laburnum are particularly prone to terminal slug attacks. (complete debarking!)

Some seedlings such as Crab Apple may develop powdery mildew or other diseases. If you can bear to, it is wisest to discard the affected ones as they will always be prone to the disease. By only growing on the strongest, disease resistance can be assured.

Lift trees after a year and trim any overly long roots. Re-planted in the ground, with the roots spread radially if further trunk girth is required, or move to a deep training pot to begin its refinement.

Some trees develop surprisingly rapidly, given conditions that they prefer. e.g. A two year old larch seedling, that was about the thickness of a pencil. This was planted in deep, well drained, fertile clayey loam alongside the top of a sunny retaining wall. As it was in a herbaceous border, I left it largely to its own devices, with just an annual winter trim of the ends of long growths. It received no fertiliser but was watered during drought. In five years the trunk had grown to a girth of 46cm (18"). The bark had developed craggy fissuring over much of its height. It transplanted well and has spent two years in a training box being wired and refined.

If you are unable to plant out, the second best option is to pot up regularly. The tree should be carefully moved to a larger pot almost as soon as the roots fill the current one. The new layer of soil at the base and sides will keep the tree in good fettle and promote much more rapid growth than in a pot bound specimen. The additional effort involved in spreading the roots radially at the start is beneficial now as minimal root disturbance allows faster growth.

Happy Accidents!

A plastic bin bag of leaves was tipped out in mid summer to see if the leaf mould was ready. Inside several conkers had germinated in less than ideal growing conditions. They had grown leggy stems that spiralled around in their search for light. If left a few more days without light and water they would probably have died. I potted them up and placed them in part shade for a week. The resultant contorted trunks could probably have been achieved by severe wiring but these curves are "natural" and, peculiar though they may be, I hold some hope for interesting specimens as they age.

Two handfuls of ash seed were left to stratify in pans between larger potted trees in the garden and forgotten. They germinated strongly but unnoticed and I never did get around to pricking them out. I am now the proud owner of two highly unusual "natural" mame forests of dwarfed ash. The technique is now employed whenever I have a surfeit of seed. This is how a "fallen cone" or "one hundred tree" style may be most easily and convincingly achieved.

On to Cuttings

All Text & Photographs © Kevin Bailey 1998 - 2008