Correct Methods and Techniques for Summer Pruning of Bonsai

Pruning is a very important part of seedling cultivation and maintenance work. According to the growth and dormancy periods of seedlings, pruning can be divided into growing-season pruning and dormant-season pruning, also known as summer pruning and winter pruning. Winter pruning is from December to January of the following year, while summer pruning is from April to August of the same year. Summer pruning is mostly carried out during the growing season of flowering plants or after flowering. It mainly involves cutting shoot tips, pinching, leaf removal, and cutting off dead branches, diseased branches, and leggy branches, and should be carried out at the right time according to the growth condition of the seedlings and cultivation requirements.

Summer pruning of bonsai is very important. Through summer pruning, nutrients, water, hormones and other substances needed for growth within the plant can be reasonably distributed, and the effect is faster than winter pruning. At the same time, summer pruning can reasonably and promptly reshape or maintain the tree crown form, adjust the density of branches in the crown, and improve ventilation and light conditions, thereby enhancing the ornamental effect of the bonsai and increasing its flower and fruit quantity.

Basic Principles of Summer Pruning

1. Maintain ventilation and light penetration in the tree crown. Ventilation and light penetration are not only beneficial to tree growth but can also effectively reduce the occurrence of pests and diseases. Therefore, some overly dense branches should be thinned out to keep the tree well ventilated and lit. This is especially important for flowering shrubs such as Prunus triloba (flowering almond) and Prunus persica 'Duplex' (ornamental peach). When necessary, measures such as leaf removal can also be taken.

2. Pinch back promptly to prevent leggy branch growth, which helps increase the lignification degree of new branches and is also somewhat beneficial to flower bud differentiation.

3. Promptly thin out or cut back some diseased and pest-infested branches to prevent the spread of pests and diseases.

4. Promptly remove root suckers. Tree species such as Platanus orientalis (oriental plane) and Cercis chinensis (Chinese redbud) are very prone to producing root suckers. Timely removal of root suckers not only reduces nutrient consumption but also prevents them from disrupting the tree form.

Basic Requirements for Pruning

1. The cut should be smooth and must not split.

2. When cutting back branches, an outward-facing bud should be retained, and the cut should be 1cm above the retained bud position.

3. When pruning large branches and thick roots with a diameter of 2cm or more, the cut must be smoothed flat and coated with preservative.

Different Pruning Requirements for Different Seedlings

1. For newly transplanted trees, summer pruning is crucial. Newly transplanted trees, especially those transplanted in spring and given a trunk cut with the top removed, will produce a large number of new branches below the cut. When these branches grow to about 40 cm, the main branches should be selected and retained. The retained branches should each occupy one direction, with spacing between branches above and below, so that no bottleneck crowding occurs. All other branches can be thinned out.

2. For shaped seedlings, branches that affect the tree form should be promptly thinned out or cut back, such as shaped Ligustrum quihoui (waxleaf privet), Euonymus japonicus (evergreen spindle tree), Fraxinus chinensis 'DuiJie' (grafted white ash), and shaped Pinus tabuliformis (Chinese pine). It is worth mentioning that many people believe summer is a period of vigorous tree growth, so shaped seedlings can wait until autumn for pruning. However, once shaped seedlings grow wildly, it is very difficult to achieve the best ornamental state with a single effort. Therefore, during the growing season of shaped seedlings, it is wise to prune branches affecting the shape at any time.

3. For flowering shrubs that bloom in summer, pruning should be carried out immediately after flowering, such as Lonicera japonica (Japanese honeysuckle), Lonicera maackii (Amur honeysuckle), Sorbaria sorbifolia (false spiraea), and Hibiscus syriacus (rose of Sharon), to prevent fruit set from consuming nutrients.

4. For shrubs that bloom multiple times, such as Rosa chinensis (Chinese rose) and Lagerstroemia indica (crape myrtle), spent flowers should be cut off at any time so that terminal flower buds form early, leading to earlier and more abundant blooming and a shortened flowering interval.

5. For some fruit-ornamental tree species, fruit thinning should be carried out reasonably so that the retained fruits have a higher ornamental effect.

Pruning Methods for Different Seedlings

01

Tree Category

1. Tall deciduous trees with an obvious main trunk should maintain their original tree form, with appropriate branch thinning. The retained main and lateral branches should be cut back at healthy buds, and 1/5 to 1/3 of the branch can be removed.

2. For deciduous trees without an obvious main trunk and with dense branches, trees with a trunk diameter of 10cm or more can have branches thinned to maintain the original tree form; for seedlings with a trunk diameter of 5-10cm, several lateral branches on the main trunk can be selected and retained, and cut back while maintaining the original tree form.

3. Dense-branched evergreen trees with rounded crowns can have branches thinned appropriately. Seedlings with branches and leaves concentrated at the top of the trunk do not need pruning. When evergreen trees with whorled lateral branches are used as street trees, 2-3 layers of whorled lateral branches at the base can be removed.

4. Evergreen conifers should not be pruned; only diseased branches, dead branches, weak-growing branches, overly dense whorled branches, and drooping branches should be removed.

5. For trees used as street trees, the trunk height should preferably be greater than 3m. All branches below the first branching point should be removed. Branches above the branching point should be thinned or cut back as appropriate, and the original crown shape should be maintained.

6. The crowns of precious tree species should only be lightly thinned.

02

Shrub and Vine Category

1. Bare-root seedlings with soil balls or with native soil from moist areas, and flowering shrubs that differentiated flower buds the previous year, should not be pruned. Dead branches and diseased or pest-infested branches should be removed when present.

2. Large shrubs with dense branches can have branches thinned appropriately.

3. For grafted shrubs, sprouting branches from the rootstock below the graft union should be removed.

4. For small shrubs with obvious branching and flower buds borne on new branches, appropriate heavy pruning should be carried out according to the tree's growth tendency to promote new branch growth and renew old branches.

5. For trees and shrubs used as hedges, shaping and pruning can be carried out after planting according to design requirements. Hedges already shaped in the nursery should be trimmed after planting.

6. For climbing and trailing seedlings, excessively long parts can be removed. For seedlings climbing on trellises, crossing branches and horizontally growing branches can be removed.

Featured Content