Bonsai: the art of growing miniature trees

The art of growing miniature trees, which rarely exceed two feet in height, is a living art form. The Chinese and Indians are reputed to have grown miniature trees in the eighth century A.D., but by the tenth century the Japanese had taken up and developed the idea. ‘Bonsai’ is, in fact, a Japanese word meaning ‘trees growing in shallow containers’. Bonsai are kept small by pruning and by keeping them in a small container which restricts their root growth. Those grown over two feet are usually left outdoors, those 1-2 feet high stand alone indoors and those less than one foot high are often grouped – two or more growing in one container. There is specialist bonsai equipment to help you shape and prune the trees.

One of the traditions of grouped bonsai is that an uneven number of trees is usually grown. This is because the Japanese regard uneven numbers as representative of longevity. A group of four trees is never grown, as the word four in Japanese is similar to the word for death.

A Eurya (Eurya emarginata) bonsai on display a...

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Which trees to choose for Bonsai

In general the slow-growing or small trees are best for bonsai, as you then have less of a struggle against nature. (Slow trees can take 50 years to reach 20 feet, whereas fast-growing ones can exceed 100 feet in the same time.) Evergreens are popular and vary little from season to season, but you can also grow flowering and fruit trees. (Choose those that have small fruit – crab apple as against eating apple.) The trees should have small leaves, or short needles, which do not detract from the perfect, miniature look of the tree.

The leaves will be small on bonsai because of the pruning and dwarfing process but, again, if you choose a small-leaved tree you will have a head start. Many types of tree not usually regarded as bonsai can be successfully grown in miniature form, so if you see anything that looks suitable it is worth attempting to grow it. But first find out as much as possible about the habits and soil preferences of the tree – the more you know about it the greater your chance of growing it successfully as a bonsai. Below are listed some of the more popular bonsai. They are all reasonably hardy and easy to keep alive.

  • Abies (Conifer). This exceptionally beautiful evergreen has short needles and a trunk which is wide at the base but tapers sharply.
  • Acer. The deciduous Acer family includes Acer Palmatum (Maple) and Acer Pseudo-plaianus (Sycamore) which both have attractive leaves.
  • Betula (Birch). A graceful deciduous tree with small foliage and white or silver bark.
  • Chamaecyparis (False Cypress). An evergreen which is obtainable in various forms, and has very small leaves.
  • Cornus Mas (Cornelian Cherry). A deciduous tree which has small yellow clusters of flowers in early spring and edible red oval fruit later.
  • Cotoneaster. The many varieties of this tree – both deciduous and evergreen –  have small leaves, flowers and fruit.
  • Fagus (Beech). This deciduous tree has a well-shaped trunk and pale green leaves in spring. The leaves turn to russet in autumn but stay on the tree throughout the winter.
  • Juniperus Communis (Juniper). A very small-leaved evergreen.
  • Lycium (Boxthorn). A deciduous tree with small purple flowers and red berries.
  • Malus (Crab Apple). A number of varieties of this deciduous tree are suitable for bonsai. It has small red or white blooms in early summer and small colourful fruit in autumn.
  • Moms Alba (Silkworm Mulberry). With its many small flowers and dark green leaves the form of this deciduous tree is particularly good.
  • Picea Abies (Spruce). A shallow-rooted evergreen with fine-needled foliage.
  • Pinus (Pine). The most popular of the bonsai and the Japanese symbol of life.
  • Prunus. The deciduous Primus family includes the Prunus Mume (Apricot), Prunus Jamasakura (Cherry) – which dislikes pruning, and Prunus Communis (Almond). The Apricot is perhaps the easiest to grow. Choose a small-leaved and small-flowered variety.
  • Pyracantha Coccinea (Firethorn). A deciduous tree which has small leaves, and tiny white flowers in mid-summer. These turn to yellow or red berries in autumn, and last for about five months.
  • Quercus (Oak). Another deciduous tree, oak is particularly good for bonsai as it is slow growing and has lots of branches.
  • Salix (Willow). A deciduous tree, Salix Babylonica (the Weeping Willow) is particularly lovely.
  • Taxus (Yew). A hardy evergreen whose trunk naturally looks gnarled as the tree grows. It also produces attractive scarlet berries.
  • Tilia x Europaea (Lime). This lovely deciduous tree has red twigs, and small, pale green, heart-shaped leaves.

To buy or to grow?

There are basically two ways of obtaining a bonsai – either you buy it or you grow it. If you buy one you lose some of the absorbing work of pruning it and determining its shape, but you do see a mature end result.

You can buy one fully grown, container and all, from a specialist nursery. Or –  from autumn to spring when they are resting – you can buy one grown but ‘root-wrapped’ (that is, with its ball of soil protectively wrapped in some way) rather than in a container. You then plant it yourself, which means you have the choice of container. Alternatively, as bonsai are usually rather expensive to buy, you could grow your own from a seed, seedling or cutting. Oak, Willow, Beech, Sycamore, and Conifers are easy to grow in this way if you give them enough warmth, moisture and air. The drawback here is that it can take up to 100 years to develop a mature bonsai!

A Japanese Maple (Acer palmatum) bonsai on dis...

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The major points to look for when buying or growing a bonsai are that the plant is small and attractive, that the trunk is thick in proportion to the height, that the plant itself and its roots look healthy, and that it has small leaves.

How to grow bonsai

An Acorn or Chestnut will grow if you plant it. You can take a cutting from a tree. Or, if you are lucky, you may find a suitable seedling. Cuttings should be 3 inches long, cut just below a leaf node so that they can drink easily. Take soft wood cuttings in the spring, and hard wood ones in autumn choosing wood of that year’s growth.

To plant, make holes in the side and bottom of a pot (if it is clay you will need to drill these, if plastic you can make them using a sharp knife). Put crocks and gravel at the bottom of the pot to help drainage, then fill the pot with a sandy compost. A seed should be planted about its own height below the soil, a cutting about one third of its length, and a seedling as a plant. Leave half an inch at the top of the pot for watering.

As roots come through the holes in the pot snip them off, and after one year in the pot if it is a cutting or seedling, or two or three years for a seed, repot into its new container and, later, start pruning the top growth very carefully.

Watering Bonsai Trees

Water bonsai about once a day, never allow the soil to dry out, but be careful not to overwater. The soil should be kept just moist at all times. You will need to water more frequently in hot weather and in the growing season and less in winter. The larger leafed varieties of bonsai should have their leaves sprayed occasionally. But never do this in the heat of the day or while the tree is receiving direct sunlight. Sun on water droplets has the same effect as a magnifying glass – the leaves will be burnt or scorched.

Soil for Bonsai Trees

Use different grades of coarse mixed soil which are suitable for your particular tree, some water retentive and some open and porous. If you use too fine a soil it will clog down when watered and not enough air will be able to circulate around the roots. Put the coarsest soil in the bottom of the pot, above the crocks, and the finest soil on top and around the roots.

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Feeding Bonsai Trees

Bonsai, like pot plants, need regular feeding with a liquid fertilizer during the growing season. This is because their roots are restricted as to the area they can stretch out to in search of food.

Re-potting

This is best done in the dormant season when the plant is not growing. So, repot spring-flowering trees in autumn, deciduous trees in autumn or early spring, and conifers any time except midsummer and mid-winter. Young trees, obviously, need repotting more frequently than old ones as they grow more quickly. To see if a tree needs repotting look at the bottom drainage holes, if more than two or three roots are poking out then it needs repotting. (If, on the other hand, none are visible some time after repotting check the plant, it is a sign that the roots are unhealthy.) Let the soil dry out before repotting to make it easier to remove. Loosen the soil from around the roots, then repot with dry soil as this will not clog and prevent air circulating around the roots. Water well, and then leave the tree in a protected place – in the garden if there is no danger of frost – for a few days to recover and settle in.

Root pruning

This is done when repotting and does not, in itself, dwarf a tree – rather it promotes healthy growth. The fine roots feed the tree and the larger ones hold it firmly in the ground. Carefully knock off most of the earth, then trim the large coarse roots as, clearly, they are not really necessary to bonsai. Also remove any broken and dead roots. There should be a space of f-1 inch between the root ball and the side of the container.

Pruning roots in this way also helps to ensure that they get enough air. Too many roots tangled together (or heavy soil) prevent this. Remember to use a sharp tool when pruning the roots to avoid damaging or bruising them.

Bonsai Wiring

Wire is twisted around the trunk or branches of bonsai to encourage growth in a particular direction, or to develop a gnarled-looking twist. Do not wire immediately following repotting as you must allow time for the plant to settle. Use copper wire – except for Cherry trees or young delicate shoots where pipe cleaners should be used. Do not wire unnecessarily and be careful not to damage the branch. Remove the wire as soon as the branch is set in its new position.

When wiring the trunk of the tree the end of the wire must be anchored so that it is taut enough to pull the trunk in the required direction. You can do this by inserting the wire through the drainage hole while you are repotting, and then leaving it on the surface of the soil until you are ready to wire the trunk.

Top pruning

Bonsai are pruned to give them shape and a bushy appearance. This should generally be done in spring. Never prune roots and the top growth at the same time, as this will give the plant too much of a shock. Cut off the top tips to get a bushy look. And prune carefully to give the tree the desired shape. Think about the final shape you want the tree to have, and consider the angle from which it will be seen. (If you buy a ready-grown bonsai you will of course only have to trim it, its basic shape will have been established long before you bought it).

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