These notes can provide no more than a very brief outline of bonsai care, but may be of some help to those who have perhaps just purchased their first bonsai, or are still at the beginner level, or are just curious to know a little more about bonsai. There are many excellent books available which will provide information and advice in much more detail, but there is no substitute for the hands on experience which can be obtained by joining a bonsai group, and attending meetings, demonstrations and workshops.
The art of growing miniature trees in pots originated in China, where they are known as penjing. The inspiration for this was observation of naturally stunted trees growing in exposed places such as cliffs in the mountains and river gorges, or on sea cliffs, and it seems that the first penjing were specimens collected from the wild from such places. In time it was realized that it was possible to train trees confined in pots to look like these naturally stunted trees. The art of growing miniature trees reached Japan many hundreds of years ago, and developed on somewhat different lines, under the name of bonsai, which means “tree in a tray”.
Bonsai range in size from mini bonsai (mame) which grow in small, dainty pots which can easily be held in the palm of a hand, through small to medium size bonsai (the vast majority), up to very large bonsai which can require two or more people to move, as in the case of the large bonsai olive.
Bonsai are displayed artistically in carefully chosen pots which suit the type of tree being grown, and the style of the bonsai. The aim is to create an illusion of age, so the appearance of a bonsai is of more importance than its actual age. This illusion of age is achieved by wiring of trunks and branches into more sinuous and gnarled shapes, exposing roots (nebari), and by other more pecialised techniques such as carving of trunks and major branches, and deliberately creating dead wood (jins) to give a more aged look.
The Japanese have developed many different styles of bonsai, but the most frequently used for single trees are formal upright, informal upright, slanting, semi-cascade and cascade.
There are many other styles, including group plantings, rock plantings, landscapes, and root over rock plantings. The Japanese approach to bonsai is fairly rigid, and many Australian bonsai growers stick closely to the rules used by Japanese bonsai growers. However, there has been a tendency in recent years to develop a more distinctively Australian approach, especially when growing Australian native plants as bonsai, which lend themselves to a more informal approach.
Bonsai growers use various approaches to creating bonsai, which can range from what is sometimes referred to as “clip and grow”, starting from small trees and pruning and shaping as the tree grows, to sometimes dramatic cutting back and shaping from older, more advanced trees from nursery stock, or trees dug from the wild. Permission for such digs needs to be obtained, whether on public or private land, and some areas, such as National Parks and Reference Areas, are strictly off limits at any time. Like most bonsai clubs, Bendigo Bonsai Club organises such digs.
The following notes give some basic guidelines for bonsai care, but it really comes down to a combination of art, in designing a bonsai, knowledge of bonsai training techniques, and of good basic horticultural practices needed to keep bonsai growing healthily.
GROWING CONDITIONS
Firstly, and most importantly, bonsai are not indoor plants.
It is nice to have a “tree of the day” on display inside, but most should not be inside for more than two or three days at a time, so rotate your indoor bonsai display. Low light levels and dryness quickly lead to lanky, weak growth, which will weaken the plant, and eventually kill it. There are plants, such as figs, which will tolerate being indoors for longer periods, but, on the whole, it is better to be sure than sorry. Bonsai need to be housed outside, ideally in a position which receives morning sun and afternoon shade, and where they will get the benefit of any rain. They should be placed on benches or stands which allow good air circulation. A shade house, or some other kind of shade structure, is beneficial for species which do not cope well with our hot summers, and may suffer from leaf burn.
Watering
Because bonsai pots are shallow, the soil mix dries out more quickly than in the deeper pots used for most other container plants, and roots can burn if the containers get too hot. When the weather is warm and dry, daily watering is desirable, and in very hot weather they need watering at least twice a day. This was a real problem for bonsai growers in Bendigo and surrounds, because of severe water restrictions during the long drought years, and most put in tanks to help keep their bonsai alive. Even though a hand held hose can now be used at any time, if tank water is available, use that rather than chemically treated tap water.The lifting of restrictions has made it easier to care for bonsai in summer, but extra care needs to be taken during heat waves. There are various ways of coping with summer heat, such as placing shallow water trays under larger bonsai pots, partly immersing small bonsai in damp sand, and covering pots with hessian or some other protection. Dunking (immersion of the pot in a container of water deep enough to cover the soil surface, until it stops bubbling) will also help get bonsai safely through heat waves. If the soil in the pot has dried out, the bonsai will feel light when picked up. Observe the difference in weight between a dry pot and a nicely saturated one, to be able to judge whether dunking is needed.
Frost
Frost can be a problem for some evergreen bonsai, such as figs, and rain forest plants such as Lilly Pillies and their relatives, especially in an inland climate like Bendigo’s, where subzero
temperatures are often experienced overnight in winter, and can be lethal to frost tender plants. Frost protection is advisable from late autumn to early spring for such bonsai.
Potting Mix
At some point after purchasing or starting off a bonsai, it will need to be repotted (see next section), and the question of a suitable potting mix will arise. Commercial bonsai potting mixes are available, but they tend to dry out too quickly in our summers, and this can lead to the loss of plants when temperatures are high and the humidity low.
Potting mixes for bonsai should be free draining, but also moisture retentive. The addition of some washed sand (free of silt and clay), some fine gravel, and a moisture retentive additive, such as peat moss or leaf mould, helps in retaining moisture longer. It is also a good idea to incorporate some slow release fertiliser in the mix (see section on fertilising for more on this.). Buying a good quality potting mix, and modifying it with these ingredients provides a satisfactory mix.
Repotting
The timing of repotting has to be geared to the needs of different types of plants, but, essentially, deciduous trees should be repotted in late winter – early spring while still dormant, and conifers and evergreens (including Australian native plants) may be repotted in either early to mid-autumn or mid to late spring (timed to avoid frosts), depending on the variety. Some native plants respond well to root and foliage pruning in early to mid-summer. Refer to bonsai books for more information, but keep in mind that you will need to adjust the timings by six months if the book was written for Northern Hemisphere readers.
Root pruning
This should be done at the time of repotting. This is probably the hardest bonsai technique for beginners to come to grips with, and yet is the essential basis for creation of a good bonsai. The concept is simple – keep the roots and top growth in balance, and encourage healthy feeder roots. When a plant is being repotted, the roots should be teased out, and cut back by about a third to a half. The remaining roots should then be spread out over new potting mix in the bottom of the pot, and then covered with more potting mix. For beginners, watching somebody else do it before doing it yourself is a good idea.
Fertilising
Bonsai need regular feeding to grow well and remain in good health. Slow release fertilisers should be incorporated in the potting mix when planting or repotting, and bonsai will also benefit from applications of dilute liquid fertiliser during the growing season. Regular applications of a seaweed extract such as Seasol help to keep leaves healthier, and less prone to burning by hot winds. Because plants differ quite widely in their nutritional needs, it is necessary to have, or to acquire, some basic horticultural knowledge of their requirements. For example, some Australian native plants such as Grevilleas and Banksias should never be given high phosphorus fertilisers, because they have evolved to efficiently extract the minimal phosphorus in Australian soils, and can literally die of an overdose.
Pruning and wiring
The techniques used to shape a bonsai involve pruning, and/or wiring of trunks and branches to allow bending them. Copper or aluminium wire is wound spirally around trunks and branches, and this allows them to be bent into shapes which improve the design of the bonsai. The wire is removed when the trunk and/or branches have set in the new position. It is very important that the wire be removed before the trunk or branch expands with growth, because the wire will cut in, and spiral grooves will be visible when it is finally removed. These scars can take a long time to heal and will detract from the appearance of the tree in the meantime. For larger bonsai, with thicker trunks and branches, there are some more elaborate, specialised bending techniques. These can be read about in books and bonsai magazines, but are best learnt by watching demonstrations, and taking part in bonsai workshops.
Compiled by Eric Wilkinson (Revised April 2012)