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When Should A Bonsai Be Repotted?

Bonsai are repotted whilst the tree is dormant, this reduces the stress on the tree as it is not having to supply water and nutrients to its leaves, or in the case of evergreens, the supply of nutrients from the roots is minimal. To repot and rootprune when a tree is supporting a full canopy of leaves and is actively in growth would result in loss of foliage through desiccation, as the roots are unable to supply sufficient water and nutrients to its leaves. Repotting during the growing season is highly stressful to almost all tree species and can often result in death or dramatic loss of vigour.

Therefore, Bonsai require repotting when they are dormant or when there is a minimal requirement for the roots to supply the rest of the tree with nutrients. Another factor that influences the exact timing of repotting a tree is the length of time that injured/trimmed roots will remain exposed to moisture and frosts. The rootsystem will not repair itself fully until the tree starts into growth during the Spring; this means a tree repotted early on in Winter may not repair its roots for a number of months, leaving the root tips open to infection, root rot and frost. By repotting closer to the time that the tree starts back into growth, the less time that the cut roots are left exposed to soil moisture and freezing conditions.

The best time to repot a tree is therefore right at the very end of its dormant period, just as it is about to start back into growth. The tree is still dormant, but, as the tree is about to start back into growth, the repair of trimmed roots is fairly immediate. The exact timing of this varies between tree species, and more importantly, varies according to local climate and individual plants. It is not realistic to expect to find out when to repot a particular species on a certain date as there is so much variation between different climates; as weather conditions subtly change year on year in the same geographical area, it is also not true that a tree is repotted on the same date each year.

Observe each tree to see when it is ready to be repotted. Deciduous species during the Winter, if inspected closely, will be seen to have small leaf buds that are held closely against the branch. As the tree starts to come out of dormancy, these leaf buds will start to extend, ready to open out and reveal their emerging leaves.

For further discussion please see When to Repot Your Bonsai

Most evergreen species, including coniferous trees will similarly display new buds starting to extend and emerge. It is harder to judge when to repot tropical evergreen species such as Ficus, Serissa and Sageretia that are grown indoors during the Winter in the UK and Northern Europe. Generally, these species will slow their growth rate during the shorter daylight hours of the Winter months, and it is during this semi-dormant period that they can be repotted.

Repotting and Rootpruning a Bonsai Part Two

Repotting and Rootpruning a Bonsai Part Three