During the growth of a bonsai tree, the old container may not be able accommodate the roots of the tree. At this time some repotting work is necessary to keep the plant healthy. If you find your bonsai plants’ growth is slowed down or the color of foliage is changing into some unhealthy colors, it means that the roots may not expand freely and they cannot fetch adequate nutrients for the growth needs. It is time to swap your container into a bigger one and swap the old soil with some new fresh ones.
The repotting work should be done in the early spring season before the growth has started. You should ensure that your bonsai trees are well watered during that period of time. Adequate watering will keep their roots moist which is necessary during the transport them into a bigger pot. The first step is to dig out your bonsai tree in a whole and put it into a clean space. Some tools such as knives can be used if their roots are stuck into the container. Then you need to do a thorough examination on the tree roots to get rid of any tangled roots using a knife. You may also inspect your bonsai tree to find any sign of insect or fungi infection or ill parts such as rotted roots or discoloured roots, and remove them as soon as possible.
When the trimming work is done, it is time to transport the bonsai tree into the new container. You can use some meshing materials to cover the drainage hole to avoid soil to be leaked out of the pot. You should fill a layer of fresh soil at the bottom and then put the bonsai tree into the container. Make sure that all parts of the root are evenly distributed in the container and keep the trunk upright as well. When all the soil is filled to the container, apply adequate water to the new pot and leave it in partial shade for a few days to make the plant to establish roots in their new home.
Image provided By Prl42 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons