When to Repot your Bonsai

Page 2 of 2

Part 2 of 2:

So During Which Bud-Stages Can a Bonsai be Repotted or Root pruned and When is the Best Time?

Stage One: Dormant Buds.

When the buds are dormant, the roots are also dormant. During this time the tree can be lifted from the ground or its current pot, bare rooted if necessary and repotted.

However, during this time, rootpruning will remove some of the stored energy of the tree and this will affect the growth rate of the tree during the forthcoming growing season. Any damage to the roots (either accidental tears, wounds or pruning cuts) will not be repaired until the roots are more active, leaving the possibility of dieback, loss of the root or even the possibility of infection to the site.

Trees can, and are, collected and root pruned at this time with no obvious ill-effect but there are risks to the health of the tree (that increases according to the amount of the root system that is removed).

Stage Two: Swelling Buds.

During this time the roots are coming out of dormancy but do not have to support any foliage and so can still be disturbed.

Repotting and rootpruning can be carried out safely. The closer the tree gets to Stage Three the better as repotting early will deprive the tree of some energy. However, those enthusiasts with large collections and with many tree trees to repot in a short period of time, will typically start early and repot trees that have many Swelling Buds.

Stage Three: Extending Buds

The very best time to repot and rootprune is as soon as extending buds are visible, typically in the upper branches of the bonsai. The roots are active and will repair any damage or pruning wounds quickly, the majority of the tree resources are above ground and the roots are not yet required to support any foliage.

Be warned; the extending buds stage can last a relatively short period of time!

Stage Four: Opening Buds

The majority of tree species must be repotted and rootpruned by this time or they should be left until the following year. As the first opening buds appear, the roots are required to supply moisture to the new foliage and should not be disturbed!

When to Repot your Bonsai

These Acer palmatum Kiyohime buds are in the Swelling Buds- Stage Two phase though the buds at the tips will begin to extend soon.

When to Repot your Bonsai

Elsewhere on the same tree, the first two opening buds are found, the tree must be repotted today or left until next year. Here it is very clear that the apical buds at the tip of the branch have progressed quicker than the other buds. It is when these apical buds begin to open that repotting should finish. Some weaker buds on the insides of the branches will remain at Stage One or Two and not reach the stage of Extending or Opening.

Further Notes on Spring Buds and Repotting Times

It is not easy to immediately identify the different stages of Spring Buds until you are familiar with a particular species, as their appearance differs from species to species. However, the basic descriptions of a winter bud, a slightly swollen bud, a lengthening bud and an opening bud does hold throughout all species. If you observe all of the buds on any particular tree, you should be able find and compare examples of at least one or two of the 4 stages, sometimes with 3 or 4 of the stages occurring on just one branch (like that of the Kiyohime pictured above).

Repotting can be safely carried out when the buds are swollen and extending, repotting is best carried out when the buds are extending.

Repotting can be carried out when the buds are dormant but will result in a loss of vigour in the tree until it recovers the 'energy' lost from the roots. For this reason, winter repotting (repotting when the buds are still dormant) is not advised.

There are exceptions to these rules but as a fail-safe and general indicator, repotting should not be carried when the buds begin to open.

For related Repotting Articles at Bonsai4me, please visit these pages:

Repotting & Rootpruning - Part I Why repotting is essential, how often and when should a bonsai be repotted?

Repotting & Rootpruning - Part II A photo guide to repotting.

Repotting & Rootpruning - Part III Bare-rooting a bonsai

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