What is too warm for deciduous dormancy?

I made a big cut on a Japanese Maple still in a nursery container back in November. It bled for quite some time, so I wanted to give it some extra winter protection since I live in Michigan (zone 6). I let it experience a couple light freezes (low 30s/upper 20s), and then I brought it into a north-facing 3-season room in our house. The room has stayed pretty consistently around 40-45 F. Is that too warm for sufficient dormancy for a deciduous tree like JM? What about for trees like JBP or Coastal Redwood, which I know don’t like very cold temps?

My guess is that 40-45F (4.4-7.2C) might be a bit warm for optimal Japanese Maple dormancy since they are a mountain tree. Can you set it against an outside wall and put a blanket over it to reduce the temperature a little? It is probably good for Redwood and might also be a little warm for Japanese Black Pine. One year of less than optimal dormancy will probably not cause any real issues, but several might. On the other hand, someone in Singapore posted on another forum about buying a Japanese Maple there and the average low in Dec./Jan. is 73F/23C and those are coldest months of the year!

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Thanks, Marty. That’s kind of what I figured. I actually started just shuffling it in and out to keep the temps down. That room gets pretty cold at night, and I keep it near an exterior window, which stays a full 4-5 degrees colder than the interior of the room, so lately the tree enjoys pretty consistent temps between 34-38.


There are hundreds of JM cultivars. Varieties have hardiness ratings all over the map. Ergo, their requirements for dormancy vary as well. The key is to talk to a JM grower about what varieties are suited for a 40-45 degree winter environment and buy a specimen of that cultivar. For the cultivar you already own, ask the grower what the optimum outdoor temperature range is and try to provide that environment for it. Talk to a couple of growers. Check the web.