Bonsai Cultivation Explained

Bonsai is the ancient oriental art of dwarfing trees by skilful branch and root pruning. The aim is to reproduce in miniature a forest giant or glade of trees without malformation or any indication of restriction. The results must look natural – and to achieve this calls for ingenuity and infinite patience.

The origin of the art is lost in the mists of time, although bonsai in ceramic containers are portrayed in Japanese picture scrolls of the Twelfth and Thirteenth centuries. They were also written about, although not everyone ap­preciated their charm as is indicated by the carping of Kenko Yoshida (1283-1350) in his famous Tsurezure-gusa: ‘To appreciate and find pleasure in curiously curved potted trees is to love deformity.’ True bonsai, of course, is not deformity.

Japanese bonsai

However, even earlier in time the Chinese collected naturally dwarfed pines and other trees from mountain tops and rock crevices, growing these in containers for home decora­tion. Probably the Japanese saw some of these in their regular forays into China and elabo­rated the technique. They are now masters of a craft which has spread to the western world.

small bonsai tree

Today most countries are interested in bonsai, which are more and more frequently exhi­bited at British and European horticultural shows. In the United States regular instruction is given in dwarfing techniques by exponents of the art and many Americans build special slatted greenhouses to house their collections.

Bonsai Styles

Many different styles of bonsai are recognized by the Japanese and these are named according to their shape and the angle of the trunks in the pots. An upright tree for example is called chokkan; one with a slanting trunk shakan, or semi-cascade in the west; a true cascade (kengai in Japanese) has a drooping trunk and all its growth spills downwards, which makes it ideal for tall stands. There are also trees with gnarled and twisted trunks suggesting a plant growing on a windswept cliff (hankan).

Group plantings, or bonsai with two or more trunks growing from one stump, are par­ticularly attractive as they suggest landscapes in miniature. Ishi-tsuki, literally tree with a stone, refers to a tree growing out of a stone, such as may sometimes be seen on a cliff top. Here small trees are either planted in a depres­sion in a suitable stone or the roots are trained to grow over a stone. One difficulty of group planting is keeping all the specimens equally healthy, so that enthusiasts usually graduate to rather than commence with this style of bonsai.


Bonsai in shallow pot


Bonsai means ‘plant in a tray’, a reminder that these little trees are often grown in shallow dishes – frequently only 3.75cm deep.

Shapes vary but usually conform to some geometrical design, such as a square or circle, and shallow oblongs are particularly favoured for group plantings. These may be rimless or have protruding outer or inner rims. Taller containers are used for cascading specimens which need extra support, and moderately deep round or oval dishes for individual trees, especially those grown primarily for their fruits or foliage.

While glazed pots are usual for shallow con­tainers, the deeper kinds are best left unglazed as they are more susceptible to water-logging. Colours are plain-blue, grey, black, cinnabar, dark brown or green – and there should be no ornamentation. It is the trees which matter, not the pots. Drainage holes are also essential – the Japanese call these ‘eyes’ – and to protect block­age from soil must be protected with mesh or crocks or the special unglazed, earthenware covers studded with holes (which the Japanese call ‘eyelids’) before the mixture is put in place.

For display purposes bonsai trees can be raised to eye level on a table or bench, or stood on plant stands (essential for the cascading types). Contrary to popular belief they are not real houseplants and must only be brought in­side for limited periods. The rest of the year they should stand in the dappled light of an open slatted house or on a shaded balcony. Al­though very hardy they can be damaged by sustained hard frosts so may need protection at such times. Similarly an overheated room, or sun shining on them through glass may cause damage. Plants growing indoors need spraying over with soft water several times daily (especi­ally in centrally heated houses) and regularly watered.


The mixture for bonsai trees should be rich enough to sustain healthy growth yet very well drained and aerated. Volcanic soil has these qualities and is often used in Japan, but elsewhere loam, sand and leafmould are the main ingredients.

The sand must be sharp and coarse but not salt (so seashore sand is out), the leafmould well rotted and from deciduous trees, prefer­ably oak, and the loam of a sandy nature, al­though heavier loams are occasionally used for flowering trees like wistaria, Japanese quince (Chaenomeles speciosa) and crabapples.

Kan Yashiroda, a most experienced grower at the Brooklyn Botanic Garden in New York, suggests three basic mixes for various tree 2 types. These can be amended to suit individual species. Thus for conifers, which need a very free draining mixture, nine parts sand are mixed with one part leafmould; deciduous trees have three parts sand to one of leafmould and fruiting trees two parts sand to one of leaf-mould. Good quality porous loam can replace the leafmould for deciduous trees if desired.

Bonsai Cultivation

Most bonsai trees are acquired originally from a shop or nursery. They can be expensive so it behooves the buyer to examine them carefully before purchase. The tree should be shapely and not show tell-tale cuts where branches or roots have been crudely removed to reduce its stature. The leaves should be bright and green without brown tips or spotting and dormant buds plump and healthy. The soil should feel damp but not sodden and the tree stand firmly – without rocking – in its container. The pre­sence of moss on the trunk is a good sign as it denotes age and careful cultivation. There should be at least one drainage hole in the container.

After purchase keep the plant outdoors for several weeks (except in very severe weather), before taking it indoors to nullify the effects of what may have been a long shoplife. This sojourn outdoors should be repeated from time to time. Once inside, give the tree a light place, but away from radiators, fires, or strong sunlight through glass. Spray over the foliage and water the plant regularly – twice daily if necessary – using soft water, and feed the trees in summer at 10-14 day intervals with weak liquid manure. Keep a good lookout for pests and use a weak insecticide at the first sign o( attack.

Dedicated bonsai enthusiasts – realizing that it takes years to make and minutes to spoil -never leave their trees to chance when going on holiday. One American lady of my ac­quaintance takes them-lock, stock and barrel – to her bonsai teacher, the only person she trusts to look after her valuable collection. Bearing in mind that these little trees can live for centuries and that good specimens in Japan are treated as heirlooms, such concern is under-


bonsai pine tree

standable. Lacking a suitable ‘nurse’ the trees should be grouped outdoors in light shade and have moist peat packed between and over the pots, to keep them damp until the owner returns. Nothing, however, equals the regular attention of a sympathetic gardener.

Bonsai Propagation

The usual methods of obtaining bonsai mate­rial are as follows.

(1) Starting with plants already stunted, twisted or deformed collected from cliffsides, mountains or wooded districts. The larger roots are removed, leaving the smaller to feed and establish the newly potted plant. Training takes on from there.

(2) By cuttings. A number of plants respond satisfactorily to this method, particularly gink­gos, tamarisks, Picea jezoensis and willows. Some – like weeping willows (Salix baby-lonica), tree ivies and Ilex serrata (a twiggy, slowgrowing, deciduous holly) – can be rooted from quite fat stems (up to 2.5cm/lin across), which is useful when stout trunked trees are required. They should be rooted in a propagat­ing frame. Later the cuttings are separately potted.

(3) By layers. Air layering on an existing tree in spring is the most satisfactory form of this, as one can select a well-proportioned stem or branch. The upper part of the shoot is induced to root and when this takes place the rooted segment is cut off. The first process is to arrest the flow of sap downwards by binding the branch tightly with a piece of wire at the place where it should root. To stimulate the latter the section is sometimes ring-barked, by taking out a narrow strip of bark between two parallel rings cut round the stem with a sharp knife. Very weak branches should only have a partial

ring of bark removed. The wounded area is then bound round with damp sphagnum moss, secured in its turn by a polyethylene or plastic wrap tightly fastened above and below the moss with binding tape. It then looks like a white sausage. Centuries ago clay was used to seal the wounded tissue or a section of bamboo was sliced down its centre and clamped either side of the moss covered area.

When rooting takes place (usually visible through the polyethylene or plastic) the rooted part is detached, potted and kept in a close atmosphere until it becomes established.

(4) By grafting. Grafting is practised by pro­fessionals more particularly with monaecious trees like the maidenhair (Ginkgo biloba). By grafting a male or female branch on to a bonsai tree of the opposite sex it is possible to produce fruits on the specimen. The Japanese also graft different varieties of cherry or crabapple on the same tree, which thus simultaneously produces both white and red blossoms. Such specimens are frequently offered for sale by Japanese growers in spring.

(5) From seed. Seed represents the slowest method of obtaining bonsai material but is also the cheapest. A wide range of plants can be used including pyracantha, hawthorn, beech, cotoneaster, yew, junipers, cherries, peaches, horse chestnuts, oaks, zelkovias, spruces, pines, larch, hemlock and crabapples. The berried kinds should first be stratified as this hastens germination. Spread the berries out thinly on flat boxes of damp sand and place these outside in an exposed position so that they receive the full effects of the weather – alternate soaking and drying, freezing and thawing. This rapidly breaks down the soft flesh after which the seeds will come away easily when rinsed through a strainer. Sow the seeds in light sandy mixture




tall bonsai

and they soon germinate. To protect the berries from vermin while in the garden, cover the boxes with perforated zinc or foil mesh.

Seeds which do not require stratifying are the fleshless types like hemlocks (Tsuga), pines, spruce and larch. These should be kept dry until sowing time in spring.

Training Bonsai

Bonsai trees need regular training right through their lives. The aim is not only to restrict growth but to give them an appearance of age and maturity. Pruning and wiring are the chief means adopted, the former to check over vigo­rous growth and the latter to produce interest­ing shapes.

When a seedling pine tree, for example, develops it is pinched back hard to a point just above the two cotyledon (seed) leaves. This encourages the formation of two lesser shoots rather than one vigorous central stem. Later only the weaker of the two will be retained. Growth is slow in small containers but as soon as the shoots are long enough they are twisted into an CS’ shape or bent in various designs. This operation checks development and produces ^4 unusual growth formation at the crowns.

When branches develop those which are re­tained are twisted or wired to make them take on irregular forms – horizontal, weeping, sinuous, zigzag according to the desired effect.

Copper wire is better than galvanized, which soon rusts. Electrically treated copper wire is suitable (sizes 10-20 are best), or if ordinary wire is burnt it loses its offensive, give-away brightness. Tough barked trees will not suffer from direct contact with the wire but more delicate branches should be protected by wrap­ping the wire round beforehand, using with tape the same colour as the tree.

Older trees which are to be wired should be well manured the previous season, to build up their stamina for this testing operation. If the branches are tough, withholding water for a day or two often softens them up and makes them more flexible. The usual method of bend­ing a stem or branch is to wind the wire around it in spirals. It is the spiral which keeps it in place, all without marking, and 6-12 months later when it is removed the branch will keep its shape. Never wire or bend branches in un­natural or impossible shapes and never leave evidence where tops of branches or trunks have been removed.

bonsai maple

red bonsai maple

Pruning Bonsai

Leaves, branches and roots all need to be cut back from time to time. Dead, diseased or mis­placed branches for example have to be care­fully taken out, using a very sharp pruning knife so that the wound soon callouses and dis­appears. This is normally carried out in the dormant season, but other objectives are to remove any low branches or opposite or crossing branches.

Leaf pinching, an early summer operation, is practised on such deciduous trees as maples. Some or all of the leaves are removed, a process which impels the tree to make new foliage. These new leaves will be smaller and finer.

Growing shoots are also checked as necessary throughout the growing season, simply by pinching out the shoots to two or three buds or leaves. Root pruning occurs when plants have to be repotted, normally every two or three years. After they have been turned from their containers and the soil removed, cut back old or dead roots and reduce the remainder by one-third or two-thirds according to the age of the specimen. Repot in the same sized or very slightly larger dish, using a fresh mixture.

One to Try

A good plant to practise on is the fast-growing weeping willow, Salix babylonica which nor­mally grows to more than 6m/20ft. Strike a cutting from an adult tree, using a branch about 2.5cm / 1 in thick and 45-60cm. Insert this for a third of its length in sandy soil (a propagating frame hastens root­ing) at an angle of 45°. After it roots, shoots will develop and any of these which run up­right – and so lose their weeping habit -should be tied down to a bamboo cane in­serted at an angle in the soil mixture. The following spring, pot the plant separately in a small container-still keeping the trunk at an angle-and cut back all shoots to two or three buds. Eventually the pot will become rootbound and when this occurs take the tree out, shake off the soil and severely prune the roots before repotting. At the same time take the shoots back again to two or three buds.

By repeating this procedure the tree will adopt a most interesting shape with long trailing branches. The angle of the trunk will enable these to droop over the edge of a plant stand or similar raised support.

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