How to Perform a Successful Repotting!

Claude Savard

The repotting process for a bonsai tree is of crucial importance as it preserves the fine feeder roots necessary for the tree’s nutrition while eliminating overly bulky secondary roots. This process contributes to the reduction of the tree’s size, known as miniaturization.

The frequency of repotting varies depending on the species and the vigor of the trees. A young tree may be repotted every two or three years, depending on its growth. On the other hand, for older trees in the maintenance phase, repotting can be done every five years or even longer, according to the advice of some renowned Japanese masters.

It is essential to plan your interventions on your bonsai trees to avoid unnecessary stress. Normally, only one major operation should be carried out on your tree during its growing season. You can choose to perform a repotting, carry out significant wiring, or perform large bending techniques.

Repotting is generally done in spring, during a very short period. This can last a few days to one or two weeks, depending on the species. It is crucial to conduct repotting before the buds start to open. In regions where spring temperatures can drop below zero degrees Celsius, it is important to ensure that recently repotted trees do not experience freezing conditions.

American larch / Larix laricina

The ideal time for repotting larch trees is quite short. It is recommended to carry out this operation when the buds begin to swell and turn beige in color, and continue until the first needles appear.

According to many professionals, this time window provides the best chances of successful recovery for the trees.

As for the next image, it showcases the budding of a Chinese Elm tree. The buds are just beginning to open, signaling the start of the repotting season for many deciduous trees. This period can extend until the emergence of the first leaves.

Chinese Elm / Ulmus parvifolia

For enthusiasts who keep their bonsai trees in a cold greenhouse, maintained between two (2) and five (5) degrees Celsius during winter, repotting can be done from January to March, always before the buds fully unfold.

Here are some steps to facilitate the repotting process:

1. Prepare the substrate and all the necessary tools for repotting.

2. Gently remove the tree from the pot and check the condition of its roots. Use a chopstick to remove the old substrate, starting from the sides. If necessary, trim any excessively long or thick roots.

3. Prepare the pot to accommodate the tree. Make sure you have a mesh and anchoring wire available.

4. Add a layer of substrate at the bottom of the pot and create a small mound beneath the tree to properly position the substrate.

5. Secure the tree in the pot using the anchoring wires.

6. Begin layering the substrate in stages, ensuring it penetrates well between the roots.

7. Use a chopstick to make circular movements in the substrate, ensuring even distribution and eliminating air pockets.

8. After repotting, thoroughly water the tree.

9. Conduct regular checks in the following days and weeks to ensure the tree is recovering well.

Note : Photos graciously provided by Mr. Brian Donnelly and Groupe Bonsaï Québec.