Why do we repot bonsai?
In nature trees root deep into the ground to sustain the tree but since bonsai live in a pot they only have limited space to grow their roots and to remain healthy every once in a while we have to repot our bonsai but also to ensure the key features of a good bonsai soil, if you don’t know what a good soil is I recommend reading the the bonsai soil page in the library first.
Beside the two reasons above we also repot to motivate a radial pattern of roots not growing directly down but spreading outwards all around the base of the tree creating the image of a well established old tree, In Japanese this is called the Nebari.
added on top of that when training a tree into a bonsai one of the goals is to plant our future bonsai in a shallow container and often to reach that goal multiple repots are needed to reduce the downward growing roots and keep only the ones that will aid in a good nebari!
Timing is crucial
regardless how big the urge is to repot your tree because it is not in a proper bonsai soil its really important to realize that you can not just run outside and repot your bonsai whenever you like!
if its not the right time to repot yet or have not prepared properly its often better to just care the best for your tree until its the right time to repot or wait until you have prepared for it.
If you are planning on repotting or digging up trees from the ground doing this at the right time is key to be successful doing it.
doing it at the wrong moments can result in dead trees and nobody wants that!
In general the right time to do a repot or start collecting tree’s is in spring when the tree shows signs of waking up when the buds swell and the tree is getting ready to start growing.
this is the perfect time for doing root work as the tree will start growing soon after the repot it will start recovering and growing new roots.
More information about how to repot is to be found in the Techniques section here