Depends :-) J. maples need at least 1000 hours of temps below 40F (~4.5C). Can it get that outdoors before it gets too cold? Or will it receive any additional requirements in the sunroom (heated? average winter temp?)? Temperatures much above the 40F mark will encourage the plant to break dormancy. And while these can go through an extended period without full or sustained dormancy occuring (lack of adequate chill hours), it is usually a short term situation at best.

"Species that have well developed dormancy needs cannot be tricked out of them. If you attempt to give a such as species, for instance Japanese maple, Acer palmatum, an eternal summer by bringing it in the house, it will grow continuously for as long as two years. After a maximum period of sustained growth, a temperate climate plant will automatically go dormant no matter what the season or condition. Deciduous plants will lose their leaves, evergreens will curtail all new growth. This is very stressful to the plant and usually fatal. It will be 100% fatal if the plant does not receive the necessary period of cold temperatures required to break the dormancy."

Japanese Maples grow very well in Charleston, SC....do they get 1000 hours below 40F?

Problem with zone 3a, you could hit -20F before December 1st. The sunroom though is probably too warm though...you want a cool greenhouse.

Japanese Maples grow very well in Charleston, SC....do they get 1000 hours below 40F?

Yes. Average winter low temperatures along the coast is 38F -- inland 32F.

Generally any zone 8 climate is suitable for growing JM's, even zone 9 (minimum average winter lows of 20-25F). It starts becoming more difficult in zone 10, which is usually considered "frost free" (although even southern Florida and the San Diego area can experience frosts).

Getting sufficient chilling time is certainly not a problem in our zone 3 climate, LOL! However, the above-ground growth, and probably even the roots, are likely to be winter-killed if you're trying to do this outdoors.

My husband grew japanese maples successfully here in Calgary. They were in huge pots, wintered over in our dark coldroom. They were exposed only to light frost outdoors before being brought in.
One "trick" he learned was to get them outdoors before they started to leaf out. If they were allowed to leaf out indoors, the foliage was soft and tender and the hardening off process was very damaging to the foliage.

"Japanese Maples grow very well in Charleston, SC....do they get 1000 hours below 40F? "
Sorry, gardengal. This set off my alarm bells, too. I don't think you've made a mistake so much as your source...which was?
I'm almost certain I've seen videos or pictures of very warm subtropical gardens with Japanese Maples. I just found a web link recommending them as a "top 5 small trees for Auckland, NZ". Well, Auckland's lowest monthly average for the whole year is only 44F. Even taking the North Island as a whole, I doubt most of the heavily inhabited bits have this chilling requirement met. They even grow in Sydney.

Here is a link that might be useful: http://www.awanursery.co.nz/product-category/deciduous-trees/

This post was edited by davidrt28 on Sat, Nov 15, 14 at 13:24

And, btw...correct figures for Charleston. Also has no months with averages below 40F.

Here is a link that might be useful: http://www.sercc.com/cgi-bin/sercc/cliMAIN.pl?sc1549