Repotting

[stevemg]

How often do we need to repot our bonsai

Chers

[shibui]

How long is a piece of string?

Lets look at WHY we repot:

• Roots must grow because only the new parts at the tip can take in food and water. It follows that eventually the pot will be so full of roots that there is no room for water and air to get in and the roots will suffer.

• Potting mix particles break down over time. Eventually the larger particles have decomposed into much smaller particles and there will not be enough room for air and water to enter the root zone. This is less of a problem where long lasting inorganic components are used.

In both cases, repotting and root pruning allow us to give the tree space to grow new roots and add fresh mix so that there is again spaces for water and air to penetrate and for new roots to grow.
We don't often think about air being important to roots but it is almost as important to plant roots as water.

Different potting mix components break down at different rates. Some potting mix will still be good after 5 or 10 years. Others will have decomposed to sludge in just a few years. How often your soil needs replacing will depend entirely on what it is composed of as well as how much water and fertiliser is used during the year.

Different species grow at different rates so need more or less frequent repotting. My banksias can fill a pot wit masses of fine roots in a single season. i repot those every year or 2
Trees grow at different rates at different ages. Younger trees tend to grow fast and make lots of roots so younger trees are generally repotted more often. young trees that are allowed to grow freely to thicken or to heal cuts are repotted every year or 2
Different sized bonsai need different approaches. I find it best to repot my smallest bonsai every year because the post fill with roots in a single season. When I miss repotting those shohin sized trees they really suffer the following summer as it becomes really difficult to get water into the roots.
You can see that there is no one right answer to how often. So many variables that even experienced growers do not work to a calendar but assess each on a case by case basis.

There are many myths and misconceptions about root pruning. Many people think it will hurt the tree and are frightened to cut any roots. I have noticed that my bonsai tend to grow far more strongly in the season following repotting. I have also noticed that almost all plants (not only bonsai) in pots gradually get less and less vigorous over years in the same pot. I have no doubts that root pruning and repotting is good for plants in pots.

[stevemg]

Ty very much for your reply it makes a lot of sense

Cheers