Confusion Over Fall Repotting-
I’ve noticed over the years a lot of puzzlement over the correct time to repot. Much of the confusion stems from placing too much weight on the exceptions to spring repotting. There’s a simple way of looking at it that might help decide when to repot.
Ron Weasley pulls up a mandrake
When we repot, the tree is essentially given the signal, ‘Hey, it’s spring, let’s grow!’ Not necessarily on top…a tree repotted in fall doesn’t often grow on top. But the roots are often as active as if it were spring, because the tree is trying to regrow what was cut off. Then winter comes. And if we’re in the north, blasts of freezing weather can obliterate that tender root system, and kill the tree.
In general, only repot in the springtime.
If you must repot in the fall, do it only if you have protection from freezing weather, such as a greenhouse.
Naturally, many exceptions exist. A few of them are:
- Some species, like azaleas, begin their extension cycle after flowering, so in some climates (not blazing hot, dry ones), repotting after flowering in late spring/early summer might be preferred.
- Spring in Lost Angeles is wintertime for most other places. LA doesn’t really have a winter, so bonsai are usually repotted in December/January.
- Trees with root problems might need repotting at any time of the year. This might be simply transferring to more open surrounding soil, even if no real root work is done, and even if the timing is not ideal.
- Yamadori collectors often find summertime and early fall to be good times, as the mountains can be hard to navigate in early spring weather, and then, a good secondary time to repot is after needle growth on pines has stopped.
- Plant nurseries sometimes repot at very interesting times of the year, like summer. But it’s best not to emulate them, as they have pinpointed when, and how much, and what kind of aftercare. Those professionals exist on the outsides of the bell curve, and they are there for a reason.
For most of us in bonsai, repotting in the springtime (whatever that is for you) will prevent a host of problems with reestablishment of the roots and growth of the tree.
Just keep in mind that repotting, translated, means ‘grow’ to a tree. And repot accordingly.