Pruning, Trimming and Pinching
During late spring and throughout the summer bonsai trees can quickly become overgrown, losing their shape and overall structure. The speed at which they grow depends on many factors, such as age, species and also the watering and feeding regime.
To keep the growth balanced and in shape, pruning is necessary and this is without doubt one of the most enjoyable and satisfying aspects of the hobby. Do not be afraid pruning - it is an essential part of the development and maintenance of bonsai, helping to create miniature trees, rather than overgrown bushes. Pruning can be a learning exercise and if a mistake is made, there is a good chance that new growth will rectify the situation!
Important points to bear in mind:
- Trees should be allowed periods of free growth to keep them healthy. There is a close relationship between new shoots and new roots, and so you can be sure that when a tree's shoots are extending, so are the roots. The extent of growth allowed will depend upon the stage of training. A tree in the development stage will benefit greatly from a period of free growth, which will help to thicken up the branches and trunk. For mature bonsai, growth should be kept more balanced and so shoots are scissor trimmed, pruning particularly vigorous shoots harder, before they begin to sap strength from other areas. The result will be shorter internodal lengths and more compact growth. However, if a branch is weak, allow all growth to extend to provide it with extra strength
- The top of the tree is the most vigorous area in most species, with the lowest branches being weaker, (azaleas and kiyohime maples are notable exceptions to this growth pattern). This should always be taken into account when pruning or trimming trees, therefore it is usually necessary to prune harder higher up the tree. If a bonsai is left to grow unchecked, the top will quickly become dominant, with the fine shoots near the apex becoming thick, ugly and out of scale
- Pinching the candles on pine trees once they are fully extended will result in back budding and compact growth. It is worth taking out the dominant central shoot, to allow more strength to be channeled into the weaker side shoots. If the candles are allowed to develop into shoots, the size and strength of the tree will be increased. These shoots should then be cut to the required length in midsummer, or have the end buds removed to encourage denser growth the following year. Removing all the candles in spring as they start to extend will produce new buds both at the tip and further back. Some of these buds will open in the same year, producing compact growth with smaller needles. By using these techniques and also controlling watering and feeding whilst the needles are opening, their length can be considerably reduced. Do not, however, aim for tiny spruce-like needles as these look unnatural and can make the tree weak
- Once a twiggy structure has become established, summer pinching is a useful technique to maintain the tree's shape and to develop greater ramification. For juniper, cypress, spruce, cryptomeria, larch and other similar conifers, hold the foliage in one hand and 'pluck' the new growth. The shoots will be removed cleanly, whereas using scissors would cause more browning at the ends, especially in dry and sunny weather. With deciduous trees, such as maples, zelkovas, elms, beech and similar species, pinch out the growing tip once new shoots begin to unfurl and extend past the first set of leaves
- Deciduous trees usually grow far more rapidly than conifers, with new shoots extending quickly
- Do not prune just to maintain a silhouette. The interior of the tree will quickly begin to die if it does not receive adequate light and ventilation, so this should be considered. Lack of light and air flow can also encourage pests and diseases. Thin out dense areas of foliage to ensure that whole branches remain healthy. Leaf pruning deciduous trees can help considerably, preventing die-back
- When pruning, if possible, leave the bud at the end of the shoot pointing in the direction in which you require the growth to extend. This practice is known as 'directional pruning' and is a useful technique which reduces the need for wiring
- If removing large branches, always ensure that the remaining wound is concave, so that it will heal neatly and quickly. Seal with cut paste or similar. An ideal time to remove large branches is during midsummer, after the initial burst of spring energy has subsided. This ensures a smaller callous and less bleeding, although branches can usually be safely removed at most times of the year. For conifers, consider the option of creating a jin
- Pruning deciduous trees in late winter/early spring enables their form to be seen clearly. However, make sure that you are aware of any branches that have died, so that you do not remove a live branch and find that you have unwittingly left a dead one! Trees that have been winter pruned will benefit by being given protection from the elements
- When removing branches, if unsure whether the branch should be removed completely, prune back hard first. Leave some buds that could grow back if desired, so that your options are left open