Growing trees from seed has a charm that begins with the joy of germination. It continues as each seedling progresses through its tender stages to become a promising sapling. This potential fully fledged tree, given the correct care over time, can become a bonsai. A tree that has been under your personal supervision for its entire life.
Many say that they have no luck with trees from seed but it’s not surprising that it can prove difficult. Think about tree seeds in the wild for a moment. Almost every mature tree produces hundreds, sometimes thousands of seed every year. How many saplings germinate and survive? Very few in relation to the seed produced.
- Seeds are a natural larder in winter and are consumed by insects, birds and small mammals. (So don’t be greedy and strip a plant or area completely of its seed.)
- Seed falls randomly and may land where successful germination is impossible; on dry rock, barren paths, drives, a lawn where seedlings will be mown, or anywhere starved of light.
- Saplings are tender morsels for passing herbivores including slugs, snails, caterpillars, weevils, rabbits, goats, cattle and sheep.
- In some years the weather conditions are unsuitable for germination, too warm or wet in winter, too dry or cold in spring.
- Young seedlings need regular rainfall until the roots have established themselves. A few days without, at this critical stage, is enough to kill many.
- Many seedlings are prone to attack by a variety of fungi. These cause the syndrome known collectively as damping off.
That any tree survives to grow into a mature specimen is basically down to overkill in the seed production department. If there weren’t so many seeds, we would never see any new trees. Success can be achieved with persistence and a willingness to experiment. Anyone should be able to achieve good results provided they follow the basic guidelines. Try to understanding how and why things occur in nature. If you remove most of the risks, 100% germination is not uncommon and, given care, this produces far more saplings than would have survived in the wild.
As I said above, most trees produce massive amounts of seed and the majority is usually viable, i.e. it has the potential to germinate and grow. Obtaining seed is often just a matter of identifying a tree and waiting for the seed to ripen. Collection of seed from friends gardens, roadside trees, hedgerows, woodlands and on country walks is a good way of securing a wide variety of plant material freely, if a little slowly.
Some sources of seed are arboreta, parks, churchyards, castles and monuments. You need permission from the owner. If you can arrange to meet, explain what you want and why, assuring them that you will act responsibly and abide by any rules.
Use a good handbook, for identification, if you are uncertain of the type of trees that you are collecting from. Examples are suggested at the end of this article. Once a tree or shrub has been identified, there are some points worth bearing in mind;
- Does the plant exhibit the characteristics that you require? Some trees are variable and may exhibit smaller leaves, shorter internodes, better autumn colour or bark characteristics. Seed grown from those trees may not exhibit any of the desired characteristics, but is far more likely to than seed from trees which do not.
- The seeds may be hybridised i.e. the result of cross pollination. e.g. European Larch crosses readily with the Japanese Larch giving rise to the Dunkeld Larch. All three are common in forestry plantations. If seedlings true to the species are required, seeds must be gathered from an isolated tree known to be true.
- Variations within a batch of seedlings are likely. This variability can be an advantage. Sow more than you think you will need and then select the best seedlings for your requirements. It is especially important to have a good number to select from, if you wish to grow a forest group or other multiple planting, where uniformity is desirable.
- Avoid seed from trees that show any sign of disease. Be an opportunist in late summer and autumn. Whenever you go walking, cycling, visiting gardens, parks or arboreta keep an eye open for seed from a likely looking tree or shrub. It helps to have storage materials with you so that the seed can be conveniently saved and labelled; envelopes, paper bags, photographic film canisters etc. The time to collect seed can vary due to the prevailing weather for the year but generally the seasonal routine is predictable. Prunus and Betula in late summer, Aesculus, Crataegus, Fagus, Quercus, Taxus, Acer, in autumn, Larix, Pinus, from autumn into winter.
Some Seeds Need Special Treatment
Maple seed are best collected as soon as they’re ripe. This is when the seed wings start turning brown. Stratify – keep them in damp sandy peat outdoors through the winter and sow in spring.
ALDER, collect some of the small, cone like seed heads in autumn and store in dry room until they open. Shake vigorously in a large bag to remove the seed. Store dry and cool before sowing in spring.Berberis hybridises easily, so an isolated plant is essential if you want true to type seedlings. Requires stratification to break down the seed coat.
Betula BIRCH seed is produced in conelets that self destruct while still attached to the tree. Pick off the ripening conelets and place them in a paper bag in a warm dry place. Shake after a day or two and thousands of tiny, papery seed will be released. To obtain good germination stratify fresh seed leaving it outdoors for the winter. Sow in a prepared bed, on the surface, as sunlight helps germination.
Cercis siliquastrum (JUDAS TREE) seed is easily removed from the pods, once ripe. Untreated seed frequently becomes mouldy and rots before germination, so dip in a copper based fungicide prior to stratifying.
Conifers Cones may be dried and shaken but dismantling using bonsai tools is often necessary. Many Pinus and some other conifers have small pointed seeds with a papery wing. Stratification is not usually necessary.
Cedrus cones remain on the tree until ripe and then the outer scales fall away revealing the seeds with a large papery wings. Remove the wing and sow densely, as these have a low germination rate.
Laburnum seed is poisonous. The pea-pod like seed cases split with a pop in late summer and distribute seed widely. Once some of the seed cases have opened collect the pods, split them and separate the black seed. They may be sown immediately in pans or direct in a prepared bed in the garden. They usually germinate well after stratification.
Fruits should be allowed to rot until they are brown and dry. They are then easily broken apart and the seed should be washed and dried. Save the seed in cool dry conditions to be sown the following spring.
Acorns collected in autumn should be carefully inspected, as they can contain maggot-like borers that leave a hole like woodworm. These seed are not viable and should be discarded. Sow the rest in a half and half leaf-mould/sharp sand mix, just below the surface. Wire mesh protection is essential as acorns are mouse magnets! Place the seed tray outdoors for the winter and strong germination should occur in spring.
Crab apples, Pomegranate and Dwarf pomegranate, Prunus, Cherry, Quince and many other fruit should be left out through winter to rot. Separate the seed, wash clean and sow.
If you can’t find or don’t trust collecting it yourself, you can purchase many types of tree seed from a reputable seed merchant. Some garden centres stock packets of mixed tree seed or seeds for bonsai alongside packets of flower seed. These are ideal if you don’t want a specific type of tree, as the selection of seeds is usually limited to a few easily grown species.
Don’t bother with bonsai starter kits. They include unsuitable little dishes which shatter in the first frost. Being a “Gift” item they often stay on the shelves far longer than vegetable and flower seed would be allowed to and are rarely stored at the right temperature. Most of the seed is unlikely to germinate.
Seed catalogues make pleasant winter browsing. Some include a section specifically for bonsai or indicate in the text species considered suitable. Some offer pre-germinated or chitted seed, which are easier for species known to be difficult to germinate. A reputable seed merchant will provide optimum storage conditions, often refrigerated, and fewer disappointments are likely to result. Even so, it pays to keep any seed trays that fail to grow in their first season, protect from birds and mice and leave them out for a winter or two of stratification. Next month part two of this article will detail the germination and aftercare of seedlings.
Some Recommended Seed Suppliers
Chiltern Seeds, Bortree Stile, Ulverston, Cumbria, LA12 7PB Tel 01229 581137 Catalogue lists hundreds of interesting seeds with a symbol to indicate suitability for bonsai. There are some that aren’t given a symbol, so a thorough read is essential. Chiltern Website http://www.chilternseeds.co.uk
Andrew Norfield Seeds Tel 01291 650306 Supply specially treated pregerminated seed, taking a lot of the uncertainty out of germination. The catalogue lists hundreds of tree seeds, most of which are suitable for bonsai.
Recommended identification books Alan Mitchell’s A Field Guide to the Trees of Britain and Northern Europe, and Bob Press’s Field Guide To the Trees Of Britain and Europe are both good pocket books for the field.J.D. Godet’s Trees and Shrubs of Great Britain and Northern Europe, and Roger Phillips’ Trees In Britain Europe and North America are larger format books that are more pictorially based and extremely useful for leaf, flower or seed identification.
There’s No Such Thing As Bonsai Seed!
Novices note – when seeds germinate, they will not automatically become bonsai. If planted out in the garden they would grow into full sized trees. All bonsai require training to become miniature versions of the full grown trees that the seed originated from.
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.
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.
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.
Rigid adherence to the times in the table is unnecessary. Good results are often obtained by leaving outdoors for nature to take its course.
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.
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.
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.
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.
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 atractive than its parent.
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.
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.
After the first seeds germinate, too close an atmosphere will encourage fungal diseases and should be avoided.
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.
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.
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.
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.