Bonsai Tree Repotting
Bonsai should be repotted every few years. The best time of the year for repotting is during spring or early summer when buds are starting to swell. The frequency of repotting depends on the plant specifications, but repotting technique is the same.
Flowering apples and cherries should be repotted in early fall. Azaleas and quince should be repotted immediately after they have finished flowering. Bonsai repotting has many advantages. It improves soil quality because soil breaks down over time. Fresh soil helps to bring more air to the roots of the plant.
Repotting process involves removing old roots making room for new ones, which helps to keep your bonsai small. Bonsai repotting also helps water retention since fresh soil holds water much longer. You can prevent potential pests and diseases by checking roots after removing your bonsai from the pot.
Repotting is very easy to do. You just need to follow these steps.
Step 1 – Tools & Materials
First step of bonsai repotting is to get all the tools and materials you need. It is very important to use high quality soil. The ideal soil mix differs for deciduous, conifers and flowering trees. To see what soil is best for your bonsai check the species profile. Make sure you are using similar soil to the type the bonsai tree was originally developed in. I buy all soil mixes from Bonsai Boy nursery. This bonsai specialized nursery has the best quality bonsai soil for all kinds of trees.
- For tropical and subtropical trees use Tropical/Subtropical Mix Bonsai Soil.
- For conifers use Conifer Mix Bonsai Soil which can be used for outdoor or indoor trees.
- For all other types use Professional Bonsai Soil.
Also, it is very important to use a good quality compost that might be a little more expensive, but is well worth it. As a general rule, bonsai will thrive in soil mix made up of equal parts of peat, sand and loam.
Besides soil, you will new container, mesh, scissors, and potting tools. New container should be clean and dry. Don’t try to reuse the old one because it would not be big enough. Use larger container that complements your bonsai in size, shape and color. 
You will need plastic mesh for covering the drainage holes of the bonsai container. Window screen can also be used. Mesh has the advantage of stopping unwanted visitors, like wood louse, from getting into the pot. I use Drainage Hole Covers from Bonsai Boy nursery that I bought online.
Step 2 – Watering
A day before repotting, evenly water the soil, providing good drainage. This will help roots quickly become established in the fresh soil.
Step 3 – Getting soil of the roots
Loosen the edge of the bonsai with a transplanting spatula and then carefully remove soil ball from the pot. Use root teaser to get compost of the roots. You can use kitchen fork, but it is better to use chopstick to avoid root damage.
Step 4 – Root trimming
After removing extra soil from the roots you should have about one-third of the roots exposed. Use root cutter to prune half of the exposed roots along with old damaged, rotten, or very long roots. Root pruning rejuvenates the tree by bringing the feeding roots closer to the trunk.
Step 5 – Preparing new container
New container should be soaked in water for a few days and dried before repotting. Cut out piece of plastic mesh big enough to cover a drainage hole of the container and place inside of the pot securing it with pieces of plastic-coated wire. Repeat for each drainage hole.
Step 6 – Adding soil
Spread a layer of well-washed pea-shingles or gravel in the bottom. Then add a thin layer of high quality soil mix. Different bonsai trees need different soil mix. For tropical and subtropical trees use Tropical/Subtropical Mix Bonsai Soil. For conifers use Conifer Mix Bonsai Soil, which can be used for outdoor or indoor trees. For all other types use Professional Bonsai Soil. You can also add Lava Rock Granules to the soil mix for better drainage.
Step 7 – Bonsai planting
Place the bonsai in the pot and adjust the soil so the rootball’s top is slightly below the rim. Then add very finest soil within ¼ inch or so from the rim to allow for watering. Use a compost firmer to pack the soil so no air pockets are left. Firm lightly with special trowel. You can also sprinkle a thin layer of pea-shingle or use bonsai moss
Step 8 – Bonsai watering
Water thoroughly and keep the tree protected from wind and sun to prevent moisture evaporating too quickly. Don’t feed until new growth is well under way.
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