I live in Ottawa, Ontario (Zone 5) and have successfully over-wintered a large (7 ft) potted acer shirasawanum jordan in my (windowless) garage. Last year it had very pale leaves before I was able to place it outside, some time around mid April. This year it is even earlier and is already budding and starting to leave out. We still have snow on the ground and sub-zero temperatures, so not yet time to place it outside. Will keeping it in the garage for a few more weeks be detrimental to the tree? Any advise would be helpful. Thanks / Ingrid
I have had this problem occasionally over the years. The problem with growing plants in a warmer location is that they break dormancy earlier--can't just put them out, can't leave them inside. I overwinter some of my trees in a dark basement, and if growth starts too early it gets long and lank and droopy. And then you have to be very careful when you do put them out or the new pale growth will burn. I've used several approaches to this problem. First, I try to keep the basement cold toward the end of winter. I shut the door and windows when it's below 25 F or so, but otherwise I leave them open, during the day and sometimes at night, to lengthen their dormancy. Second, and most demandingly, I've sometimes carried my trees outside for warm days and nights and brought them in again when it gets cold. If they've already broken dormancy, though, I keep them in full shade for a few days to protect the new growth from too much sun. This isn't much fun when you've got 50 pots, but if you just have a few it wouldn't be too bad, especially if you put the pot on a dolly or wheeled cart of some sort. Third--and I think this is the best approach, although somewhat tricky--is to take the trees outside in their pots after the coldest weather is over, but before they break dormancy. Here, in zone 6, that's about now--we'll still have temps in the 20s and probably teens, but not for long periods. I don't worry about plastic pots, but clay pots can still break from freezing. I've done this for the last two years with good results. Fourth, back when I had dozens of plants in pots that had broken dormancy inside, I accustomed them to sunlight and just left them outside. I bought a giant sheet of black plastic and covered the whole forest on especially cold nights in April. A pain, but it works. I've also buried pots in the ground over winter--that keeps the roots warmer, and roots are more tender than topgrowth. I've never grown 'Jordan,' but I would think the topgrowth would be pretty hardy in zone 5. Not certain about that, but other shirasawanums tolerate it. Hope this helps.
Thank you for your comprehensive response. I like your last solution the best, since it would allow me to keep the pots outside during reasonably mild weather and cover them when it is still cold. At this point, with snow still on the ground, our best bet would be to keep the garage door somewhat ajar to permit cold(er) air to prevent further rapid growth development. The roots would most definitely freeze in the pots if left outside over night. Both trees would survive this climate if planted in the ground; however, I do not have a garden large enough to accommodate the trees, which is why I keep them pruned for size maintenance. I shall see how it turns out. Thanks you again :) Ingrid
