Bonsai trees are potted in small containers in order to limit its nutrients. While this is crucial in growing a bonsai, after a few years, your tree will start to become pot-bound. Pot-bound basically means that your tree’s roots have grown and are taking up space that the nutrients in the soil used to. Without the proper amount of nutrients, your tree will die, which is why it is so crucial that you are repotting your tree regularly. 

How Often Should I Repot My Bonsai?

How often you repot your bonsai depends on your tree’s pot and the species of your tree. Fast growing trees, especially young trees, should be repotted every year or two. Older, more mature trees should be repotted every three to five years. These guidelines are pretty general. In fact, you can only really know when your tree needs to be repotted if you check the plant. 

Signs My Bonsai Tree Needs Repotting

Before you repot your bonsai tree, it is important to make sure your tree actually needs to be repotted. There are several signs that your tree needs to be repotted.

  • Growth rate slows
  • Discolored leaves (yellowing leaves in particular)
  • Increased amount of dropping leaves in the summer
  • Leaves losing their glossiness 
  • Reduction of leaf size
  • Falling of leaves in autumn 
  • Thinning of twigs & increased death of twigs in the winter
  • Poor water absorption in soil
  • Liverwort and algal slime forming on soil
  • Root ball visible through the soil

When Should I Repot?

Repotting should be done in early spring. It is best to repot when the tree is still in dormancy. This is so that the least amount of damage is done to your tree. During the spring, your tree does not have full-grown fulliage, so this will put less strain on your tree. 

Best Soil Mixtures

The soil you use for your bonsai trees is very crucial to the health of your bonsai. The reason repotting is necessary is because roots grow and soil breaks down every two years or so. Different bonsai elements include Akadama, Pumice, lava rock, fine gravel, and regular potting soil. Organic potting soil is not recommended on its own as a bonsai soil, but added into a mixture will do fine. 

Each tree prefers a different soil mixture, but you can use these guidelines until you figure out what your tree likes. There are two main mixtures you can use, the first is for deciduous trees, and the second is for coniferous trees. Both of these mixtures contain Akadama, Pumice, and lava rock, but the ratios are different. 

Deciduous bonsai tree soil: Akadama, Pumice, Lava rock at a ratio of  ½, ¼, ¼ 

Coniferous bonsai tree soil: Akadama, Pumice, Lava rock at a ratio of ⅓, ⅓, ⅓ 

There are a few exceptions that can be made. For example, if you are not able to check on your tree several times a day, you can increase the amount of Akadama in your mixture to increase water retention. Or, if your local climate is very wet, you can increase the amount of lava rock to enhance drainage.

How Do I Repot My Bonsai?

  1. You should first make sure you have all the tools that are needed to repot your tree. This includes scissors, wire cutters, a rootrake, and a chopstick.
  2. It is common for the bonsai to be stuck to the pot that they are potted in. If this is the case, cut the wire at the bottom of the pot.
  3. Using a rootrake, carefully remove your tree.
  4. You will now be able to determine whether repotting is necessary or not. If the roots are circling around the pot, it is time to repot.
  5. Remove the old soil with a chopstick. Start at the bottom and the sides of the tree. Be careful around the roots. Leave at least half the rootmass alone when repotting pine trees.
  6. Cut away any roots that have grown too long using a pair of scissors, but cut no more than 30% of the plant’s roots.
  7. When repotting in the same container, cover the plant’s drainage holes with mesh.
  8. Hold the mesh in place with wire.
  9. Attach another piece of wire in order to make the tree anchor to the pot later. 
  10.  Now we add in soil. First, add a layer of lava rock, akadama, or grit. These heavy soils will serve as your drainage layer.
  11. Now add a thin layer of soil.
  12. Put the tree back into the pot. Use the wires that we attached before to help the tree stay in place.
  13. Add more soil around the tree.
  14. Using a chopstick, work soil around the tree’s roots. This is to fill any air pockets around the roots.
  15. Water the tree generously.
  16. You’re done! Enjoy your newly potted bonsai!