Bonsai can live for many years. The small planters confine the roots and maintain the trees' small sizes. To keep a bonsai healthy and allow new growth, they need to be transplanted regularly. Fast-growing plants, such as willow, may need repotted more than once a year, while evergreens will only need transplanting every three to five years. Transplant your bonsai trees after you finish other seasonal care, like pruning.
Prepare the soil mix using 1 part sand, 1 part peat and 1 part loam or compost. If you have an evergreen bonsai, make the mix 2 parts sand to 1 part peat and 1 part loam. Stir until well mixed.
Remove the bonsai from the planter. Be gentle and careful of the delicate branches, trunk and roots. Lay the bonsai aside.
Dump the old soil in your compost bin, garden or yard. Clean the pot with hot water and soap. Scrub off any residue. Rinse well and dry.
Remove the dirt from the bonsai's roots. Trim off about 1 inch of the roots with scissors, untangling as you go. Cut off roots larger in diameter than a pencil and any that feel stiff. This will help develop smaller feeder roots.
Place a small amount of soil mix into the cleaned planter. Put the bonsai in and spread the roots. Adjust the plant to your liking. Fill with the potting mix.
Water the bonsai thoroughly, letting the water settle the soil. Add more soil to fill any air holes or gaps. Water again and allow it to drain.