Potting of bonsai

By Lionel Theron

The first time a bonsai is potted it may require fairly drastic root pruning. Many species of trees are very amenable to this operation provided that it is done at the correct time of year and that there is sufficient root left to support that which is above ground. Roots are pruned for a number of reasons:

  1. To fit the tree into the pot which has been chosen for it.
  2. To remove big and inefficient roots and to encourage a strong network of fine fibrous roots which can effectively take up nutrients, gases and water.
  3. To expose and arrange surface roots contributing to the aesthetics of the bonsai.
  4. To remove old or dead roots and encourage new ones.


The principle manner in which root pruning trauma manifests itself is in the loss of moisture by transpiration through the stomata in the leaves. Leaf surface area should be reduced so that there is a balance between what is above ground and the remaining roots. Unfortunately there is no formula for this, it has to be estimated. Leaf area can be reduced by the removal of individual leaves or complete branches. After root pruning trees they should be kept out of the wind and sun which encourage drying out. Newly potted trees benefit from frequent misting with water to prevent transpiration

Root pruning sets trees back and on occasion, it may take considerable time before new leaves sprout. One way of encouraging new growth is to apply growth hormones and the B range of vitamins. An excellent product, which has been in use in the USA for many years, is SUPERthrive. If the tree is watered with a SUPERthrive mix seven to ten days prior to transplanting even better results can be expected. Newly potted trees should not be fertilized for a month after root pruning. Do not confuse growth stimulants with fertilizers.

Naturally if an already established bonsai is re-potted there are far fewer problems as the tree should have a very good fine fibrous root system intact and often they need not be fully bareerooted.


bonsai-repotThis is a symbiotic association between a fungus (Mycellium) and the roots of many plants. The mycellium are a mass of branching hyphae that make up the vegetative body of most fungi.

In the mychorizal association there is a well-developed mycellium forming a mantle on the outside of the roots. This association is found in many trees and is particularly important for pines; the trees may not grow properly in the absence of the appropriate fungus. It is therefore, vital that when planting or transplanting pines to ensure the presence of mycellium.

It has been shown that mychorizal roots take up nutrients better than uninfected roots. The fungi obtain carbohydrates and B-group vitamins from the tree. This clearly indicates the value of using SUPERthrive, which contains B-group vitamins, on pines.

For maximum success try to pot trees at the correct time of year which is usually when buds are swelling.

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Grey marsh, black cloud...

Flapping away in autumn rain

Last old slow heron. ~ Anon

Random Bonsai Tip

When a tree has reversed taper or a narrowed 'waistline' above the nebari, you could do an airlayering just above the narrow section; or you could damage the cambium layer by either hammering gently with a mallet or by piercing the bark right into the cambium with a sharp object eg. scissors or an awl. You could also make deep incisions along the grain of the bark, where the healing process will cause scarring which would then thicken the trunk.