How to Make Reasonable Use of Suckers in Bonsai? A Practical Guide

A sucker (water sprout) is a vigorous shoot that sprouts from a dormant bud on an old perennial branch. It was originally a professional term in fruit tree cultivation, generally referring to herbaceous plant shoots that are weak, tender and brittle, and not long, but very tender, weak, and growing poorly, mostly a sign of the plant lacking sunlight or being over-fertilized. It is now gradually being applied to the care of bonsai plants. Most suckers are useless shoots, but this article attempts to explore them from the favorable side.

I. Causes and Manifestations of Suckers

Suckers occur in bonsai plants because the plant's normal growth mechanism has been broken, altered or weakened. They are more prominent in young trees, old trees, heavily pruned trees and damaged trees.

1. Excess nutrients with an imbalanced composition

The main nutrients plants need are nitrogen, phosphorus and potassium. When nitrogen is sufficient, the plant can synthesize more protein, promoting cell division and growth; the leaf area increases rapidly and photosynthesis speeds up, making the plant grow vigorously. Phosphorus participates in photosynthesis, respiration, energy storage and transfer, and cell division and enlargement within the plant, and can promote root formation and growth. Potassium can noticeably improve the plant's absorption and utilization of nitrogen and quickly convert it into protein, promoting reproductive growth.

In the care of young and mature stumps with relatively strong growth capacity, generous fertilizer and water management is generally used to strengthen the tree body and shorten the time to shaping. If phosphorus and potassium fertilizer are excessive while nitrogen fertilizer is insufficient, the growth states of roots, trunk, branches and leaves become imbalanced; the growth advantage of roots and trunk temporarily exceeds that of branches and leaves, and when photosynthesis appears insufficient, one or several vigorous shoots will quickly grow near a certain old bud point (dormant bud) on an old branch where the transport function is best, thereby achieving a new balance. If nitrogen fertilizer is applied in excess and other elements are insufficient, leaf area and chlorophyll increase, keeping the plant in vigorous growth for a long time and supplying large amounts of nutrients to the roots, which suddenly strengthens root function and equally easily induces suckers.

2. Vigorous tree, heavy pruning, main branches cut back

According to the Lingnan bonsai shaping method of "cutting the trunk to build branches," once the trunk or main branches of a stump have grown to a certain thickness they must be shortened and cut back, and branches that meet the proportions must be heavily pruned, to cultivate the next level of branches anew. These stumps are in the vigorous growth stage of cultivation; once the stump is cut back or heavily pruned, the balance between branches, leaves and roots is broken. Although root function is temporarily reduced, it urgently needs nutrients produced by photosynthesis in the leaves to sustain it, so new vigorous shoots quickly grow at the nearest bud position with the best cortex and vessels, to reach a new balance as quickly as possible.

3. Bark damage and interrupted transport

Bark is an important organ for a tree to protect itself from harm and to effectively transport various nutrients and water. When the bark is damaged and pathogens invade, the tree's transport tissue is destroyed or interrupted, and it will seek a relatively superior old bud point below the damaged area and quickly grow new vigorous shoots, thereby rapidly restoring photosynthesis in the leaves and supplying nutrients to the roots. In bonsai practice, the common techniques of scoring the bark with a knife to encourage budding and girdling the bark to encourage rooting are applications of the principle of disrupting the plant's transport system.

When suckers occur in bonsai, they not only disrupt the tree shape and affect its appearance, but also consume large amounts of nutrients and adversely affect flower bud formation the following year, so they generally need to be pinched out or cut off promptly.

"Whatever exists is reasonable." Since a stump has produced suckers, there must be a physiological reason of its own. We should distinguish different situations, and at different stages of stump care, according to different tree species and different cultivation goals, handle them prudently and use them reasonably to improve our level of care.

Misconception one: Remove them all, regardless of whether the tree is shaped.

Shaped stumps, out of the need to preserve their form, are subject to many artificial restrictions on growth and generally rarely produce suckers. Because the stump is already shaped, there is little need to cultivate the few suckers as reserve branches or auxiliary nourishing branches, so they are generally removed.

Unshaped stumps are mostly in the free-growing stage, where growing roots, cultivating branches, shaping and strengthening the tree are the main goals of care. During free growth, with ample water and fertilizer and good environmental conditions, the tree grows relatively vigorously, and short pruning, heavy pruning, branch adjustment and wiring are carried out continuously, which easily induces suckers. Consciously retaining some of these suckers can help the tree grow and shorten the time needed for the stump to take shape.

Misconception two: Remove them all, whether the stump is fresh or established.

A stump cultivated for less than two years after collection is generally called a "fresh stump," while a collected stump that has survived and is growing normally is generally called an "established stump." "Keeping the stump alive" is the main goal of the first stage of stump care. On the question of survival, fresh stumps and established stumps differ greatly in how branches and leaves are handled. Because an established stump has already survived and can grow normally, its suckers can be removed if they have no specific use. Fresh stumps are different: because they have only recently been collected and cultivated, are severely injured, and need to quickly restore tree vigor, and the amount of branches and leaves plays a very important role in the recovery process. The larger the initial leaf area of a collected stump, the stronger the photosynthesis, and the more nutrients are produced through the leaves, speeding up root growth; faster root healing and growth can more effectively supply water and various nutrients to the branches and leaves, promoting their rapid growth. Therefore, in the first year a fresh stump should not be excessively disbudded or pruned, and vigorous shoots certainly should not be removed at will.

Misconception three: Remove them all, regardless of species. Compared with conifers, although broadleaf trees have leaves with the same function, their functional capacity differs greatly. Because broadleaf trees have a large leaf area and many stomata, their photosynthesis is strong and respiration fast, so they grow relatively quickly; conifers are just the opposite, generally growing relatively slowly. In terms of growth speed, broadleaf trees produce new branches relatively easily, while new branches on conifers are generally relatively precious; in terms of photosynthesis, removing branches affects conifers far more than broadleaf trees. Therefore, removing branches must be handled according to the species, and especially for fresh stumps one must be cautious. At present, pine and cypress bonsai are developing rapidly in China, but some bonsai enthusiasts apply broadleaf tree handling methods when removing pine and cypress branches and leaves, which is in fact very wrong. This is especially true for collected pine and cypress stumps: pruning branches and leaves all at once and removing all useless branches, leaving only a very small amount of branches and leaves, causes the stump to grow slowly, weaken, or even die.

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