Hi, some people use greenhouses, but most bonsai are wintered either right in the ground (with or without pots), in coldframes - dugout spaces with hay or mulch (below ground) and a slanted lift-up door, or in either attached garages, unheated porches, or sheds. Much does depend on the type of tree, and your location, as well as exposure in terms of which direction the sun comes from because in the spring, trees may heat up and come out of dormancy sooner than you want, especially if the thaw is followed by more frost/freezing, which will kill trees that have begun to bud out, so often the trees will be stored on the north side of a house to avoid that syndrome. There are many, many books available, and I suggest you take a look at some reviews in the subforum of www.bonsaisite.com (under Gen. Disc.). What's really helpful are local clubs, because then you get to learn hands on, and get to pick everyone's brain, along with workshops, deals on books and trees, etc. From your zone, I wonder if you're in e.g. Michigan, or somewhere similar? There are also trees like Chinese elms and azalea, that require a version of cold dormancy, but not to the same extent as natives like maple, so often an unheated basement that stays around 40 F. is ideal. Greenhouses can be tricky, as they will 'attract' sun, unless you use shadecloth, and you get into the problem again of freeze/thaws, but they can also help if trees are budding out 'too early' for your climate's last annual freeze (late Apr/early May probably) as they can at least keep frost off the foliage. See how complicated it all gets :-)! But after a while it just becomes second nature (hauling your trees all over the place!).

Hi Lucy - I'm in Montana, actually. Sorry, I should have added that the first time. Billings, to be exact, south central Montana.

We have a local club, but frankly, I'm not really interested in joining one. I kind of prefer to do things on my own, but I absolutely can see how it would help with things like this. I'll have to think more on that one, I guess.

I really don't want to have to bury pots and such (no good place to do that), the garage is my hubby's domain, and our basement is well heated, so those won't work either. But I do see what you mean about greenhouses and messing with the freeze/thaw cycle - that makes perfect sense. I could see about taking some of the panels out in the winter so it didn't actually hold much heat during the day...something to consider, anyways.

I'll check out the reviews on that site, and go do some more reading. I may not quite be ready for this particular aspect of horticulture yet, but I'm glad I asked, and thank you for such a comprehensive answer! :-)

Lucy - great post! I over-winter my bonsai in my attached, unheated garage. Once dormancy sets in, little or no light is required.