Repotting Bonsai, how to repot your tree
To prevent a tree from being pot-bound and ultimately starving to death, regular repotting is crucial. Re-potting your Bonsai will not keep it small; instead it will supply the tree with new nutrients that it needs to grow and flourish.
How to repot Bonsai trees
It depends on the size of container/pot and tree species how often a Bonsai needs to be repotted. Fast growing trees need to be repotted every two years (sometimes even every year), while older, more mature trees need to be repotted every 3 to 5 years. Do not repot on a routine, instead check on your trees every early spring by carefully removing the tree from its pot. A Bonsai needs to be repotted when the roots circle around the root system. When the roots are still contained in soil wait another year before checking again.
Re-potting work normally needs to be done during the early spring; when the tree is still in dormancy. This way the somewhat damaging effect of repotting on a tree is reduced to a minimum, as the tree does not yet have to sustain a full-grown foliage. Repotting in early spring will also ensure that damage done to the root system will be repaired soon, when the tree starts growing.
Bonsai soil mixture
Choosing the right soil mixture is crucial for the health of your trees, it should be draining enough to prevent the roots from rotting, while absorbing enough water to supply the tree with water. Although some tree species need special soil mixtures, the following mixture is suitable for most trees:
Mix akadama, fine gravel and potting compost together in a ratio of ½ to ¼ to ¼. When you do not have time to water your trees regularly, choose a more water absorbing mixture (use more potting compost), while you should choose a more draining mixture (use more akadama and gravel) when living in a wet climate. Read the Bonsai soil article for more detailed information on soil mixtures.
Choice of Bonsai pot
Choosing a pot that fits your Bonsai, both in size as in style, is crucial for the composition as a whole. For more information, check the Bonsai pots article or the bonsai pottery page.
Repotting Bonsai, step by step
First prepare the pot, than start repotting:
- Put a plastic mesh on the drainage holes, attached with some copper wire (see photo 1, below).
- Cover the base of the pot with a layer of grit to create a good drainage. You might want to attach another copper wire to the drainage holes in the pot, which can be used to attach the tree with in the next step (see photo 2, below).
- Now use the prepared soil mixture as the second layer, on which the tree will be planted (see photo 3, below).
Step-by-step plan to repot your Bonsai:
- Carefully take the tree out of its pot, when it is stuck use a root-knife (see photo 1, below). Be sure to obtain the right bonsai tools, which makes the work easier.
- Inspect whether the tree needs to be repotted or not, as described above in the ‘how often’ section.
- By using a root-hook or some chopsticks, carefully remove the soil and disentangle the roots somewhat (see photo 2, below). When repotting pine trees never remove all the soil; this would remove the mycorrhizal fungus which is essential for the tree’s survival.
- Prune back long roots; this will help your tree to grow a more compact root-system suitable for placement in small Bonsai pots. Also remove rotting or vertical growing roots. Prune up to ¼ of the total root mass (see photo 3, below).
- Place the tree, slightly out of the middle of the pot (see photo 4, below) and attach it with the copper wire (see photo 5, below).
- Fill the pot using the soil mixture up to about 1 cm (0.4’’) below the rim; make sure the soil fills the pot completely and no air pockets between the roots are left (see photo 6, below).
- Water the tree thoroughly, this will settle the soil and fill up any remaining air pockets.
And then? Aftercare
Protect the tree from strong winds and sun for about two months. Start fertilizing one month after the repotting.
Check the Bonsai species guides on repotting Bonsai trees.
Go to the repotting forum or check our general Bonsai care guidelines.