Plants roots continue growing, even when a plant like Bonsai is in a small container or pot. When the roots become pot bound, then the bonsai needs to be repotted. If you do not repot your Bonsai, then it will become unhealthy and eventually die.
If you see the roots of your Bonsai forming a ball around the diameters of your container or pot, then it’s time to repot your plant.
To do this, carefully remove your Bonsai from the container, being careful not to remove the soil. Trim back 15% to 20% of the roots, and repot your Bonsai while adding more Bonsai potting soil to the container. Gently press the soil to remove air pockets, then water your Bonsai well.
Remember to use only Bonsai potting soil when repotting your plant. Also use Bonsai tools when trimming the roots back. If you accidentally remove more than 20% of the roots, then your Bonsai may not stand upright even once reported. You can try to save your plants by holding it up with stakes until the roots re-grow. Although this is not guaranteed to save the Bonsai, it will help support it so that it will have a chance of overcoming the stress of the excess root removal.