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How To Repot Japanese Maple Bonsai

Bonsai trees need to be repotted on the regular basis, otherwise as the tree grows, the pot will get filled with long roots. When this happens,  the drainage in the soil becomes worse and worse, and the vigor of the tree will gradually begin to decline. The tree will not be getting enough nutrients and as a result the health of the tree will begin to suffer.

Repotting is one of the those things that beginners fill uncomfortable doing, because cutting roots of the tree doesn’t seam to be a natural  thing to do. Some people are even saying that bonsai art is about tree torturing. That couldn’t be farther from the truth.

With bonsai repotting is all about keeping the tree healthy long term. That is how we manage to grow these trees for many years in very small pots and in very small amount of soil.

In this tutorial you will learn how to re-pot a Japanese Maple Bonsai, scientific name Acer palmatum. The tree has been in a nursery pot for the last 2-3 years enabling it to gain some strength and to develop roots. Now, it is a good time to get this tree into a bonsai pot.

What is the best time for repotting

A lot of people tend to repot bonsai way too early. You should repot in the Spring when the buds begin to swell and you can see a little bit of green tip of the leaf. Over the winter, all the energy of the tree is stored in the roots, so when spring comes it gradually makes its way up into the tree. At this point, the energy is in the tree, so when we prune the roots, it doesn’t reduce the vigor of the tree. Within a week of pruning, this tree will recover and grow a full canopy.

By repotting it too early, specially when the weather is cold in January, it will take a long time for the tree to start growing. You also might get some die back and the tree will have much more difficulty recovering from the work.

Items you will need:

  • New bonsai pot  – We want to repot this plant into a new container.
  • Sharp Shears – Regular shears that will be used to trim long roots.
  • Bonsai Wire Cutters – You will need to cut wire with these.
  • Root Pruners – You can use this tool to cut trunk knobs and thick woody roots.
  • Root Rake – You will use it to get out the soil of the roots.
  • Bonsai Soil Mix –  I recommend using a good quality bonsai soil mix. This is a great soil mix that has high water absorption, fast draining and good aeration.
  • Plastic Mesh – Will be used to cover holes in the container.
  • Wire – Will be used to wire the tree to the new pot.
  • Bonsai Soil Mix – This is a great soil mix that has high water absorption, fast draining and good aeration.
  • Chopsticks or bamboo stick – Will be used to pack the soil and to get rid of air pockets.

Step 1: Prepare a new pot

For this Japanese Maple we’ve chosen this oval glazed shallow pot with 5 drainage holes. These holes will need to be cover in order to prevent the soil from falling down. Cover each hole with a square piece of plastic mesh. Make a staple by bending the wire with pliers and put it trough the mesh folding both ends at the bottom of the pot.  Repeat 4 more times. When we place the tree in the pot, we’ll need to secure it with wire. Take two pieces of wire and run it at the bottom of the pot through the holes and the mesh.

Step 2: Removing the soil

Take the tree out of the nursery container. Use a single rake (you can also use double or triple one) to remove the the soil from the top of the roots. Gradually loosen it up, but don’t tear it to avoid damaging the roots.

Next, start removing soil from the bottom. A lot of the roots a the bottom will be trimmed, therefore don’t be too concerned if you identically rip some of them.

Step 3: Trimming the roots

Use sharp shears to trim down the roots. As you can see, this tree has very fine short roots. The absence of the big heavy wooden roots is an indicator of a good quality root system.

There are however some roots that are starting to circle the pot. You should trim them back to a point where we have plenty of fine fibers root left. When the tree begins to grow it will develop new feeder roots from the end where it is being cut. By bringing the feeder roots closer to the trunk, we reinvigorate  and improve the health of the tree. Over the number of repottings you can progressively build up the nebari (surface roots). There are also a few straight surface roots that you can remove since they don’t add any interest to the tree. After you are done trimming wash the roots with some water. It will help you to get rid of dust, powder and broken down soil.

Step 4: Planting the tree

Put some soil at the bottom of the pot.

Next, place the tree into the pot. Make sure to position it off center. Secure the roots with wires that you pulled through the drainage holes. Cut off access wire with wire cutters and back fill the pot with the soil. Push some of the soil underneath the flat roots of the tree.

Use a bamboo stick of chopsticks to get rid of the air pockets in the soil.

After repotting

Water the tree well and place it in the sheltered spot protecting it from bad weather especially strong winds and frost. Here is how this tree looks 10 days after repotting.

~Susan Brian

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