Trees may look like inactive sedentary creatures, but they never stop growing from shoot tips and root tips. At both the root tips and shoot tips there is a meristem that continuously grows. This gives some trees the ability to grow from hundreds to thousands of years. Now this is exciting to hear for someone growing bonsai because we want our trees to grow for as long as possible. When growing trees in small pots we can replicate a trees natural longevity and even enhance it with repotting. Below is a picture of a bonsai tree that was grown from seed in 1896. It is located at Aichien Bonsai nursery in Japan. This tree has been passed down for many generations and repotting is one of the many techniques that have kept it alive for so long. Picture was taken by Jeremiah Lee.
When a tree is confined to a container the roots eventually start to run in circles. In nurseries you will often hear this described as “root bound”. When this occurs the tree will eventually suffocate and die because of a lack of drainage and a lack of the ability to gather nutrients and water. When we repot bonsai trees we first give the roots time to grow, allowing them to fill the pot entirely. Once the roots have adequately filled the pot we trim the roots and repot the bonsai tree repeating the cycle. Every couple years or every year for some trees this cycle continues, sustaining the bonsai’s longevity.
When do we Repot?
So first, you must determine if your tree’s roots are “root bound”. This is when the roots have run out of areas to occupy and are beginning to circle in the pot. You can usually tell if something is root bound when you water. If the water is having trouble permeating through the soil, then it is probably time. Below is a photo of a root bound plant.
When you have decided it is time to repot you must do it at the right time of the year. Generally repotting is done late winter/early spring as the buds start to push, but before they open. If you live in colder climates you need to be wary about frost and wait until the last frost has finished or utilize a greenhouse. Personally, in Los Angeles California I repot many of my trees around late March.
How to Repot?
1st Remove the tree from the pot.
2nd Loosen the tree’s roots and soil with either a chop stick or a root rake.
3rd Cut off large and thick roots and leave the filamentous fine ones.
4th Remove about a third of the roots from the bottom of the tree, but be wary not to be too intrusive.
5th Place the bonsai mix in the desired pot.
6th Place tree on bonsai mix and wire the tree in if desired.
7th Using a chopstick, nestle the bonsai mix in any unfilled crevices.
8th Water the tree and you are done!