I want to repot my Maples into something more free-draining, is it too late to repot them right now? It's going to stay under 70 degrees F. this week and they'll all be under dappled light
It's not the best time to repot, but I have done it (and later, too) when a tree is clearly suffering from not enough drainage. When I figure the chances are high that the tree will be lost, I go for it.
I find it to be (one of the) the best time(s) to repot around this time of year. Initial leaf expansion has finished and major root growth is about to commence.
I rate early fall (in the UK this works out as September) as an equally good time to repot. If timed right you take advantage of a major transfer of stored energy from the leaves to the roots resulting in extensive root growth which quickly colonises the new volume of potting mix.
I agree: in Japan, bonsai growers defoliate their maples and trim the roots and branches when repotting between mid-May and mid-June. Of course, the climate is an important factor: if the weather is dry and windy, better wait until it's warm and wet. It's like a second spring for a healthy tree, and it's one one the techniques to reduce leaf size on a second growth, and the autumn colours are even better. Without going so far, if you just untangle some the roots when necessary and trim the softest shoots, your tree will have a second youth, and the operation, if carefully done, is without risks. Anyway, if the new soil and the tree are healthy, it's fewers risks of having root rot or fungal diseases.
Well, I do find that replanting after leaf out causes the tree to be shocked, and kind of stall. If the plant is already weak, this stall can really set it back; without a healthy root system to start with, I find this is a risky time. Just MHO.
