We have had a very mild winter in the Southeast, and many of my Japanese maples are starting to put out new growth now. After a week or so of 70 and 80 degree temperatures, it's supposed to dip down to the high 20s overnight this weekend. Do I have anything to worry about? Is there a temperature cutoff where new growth can be damaged? Many of my maples are in pots and could be moved relatively easy. They have been outside unprotected all winter, as our lowest temperatures have only been around 20 degress.
Dawgie, There really is no cutoff per se. We are in the same situation here, as leaves are emerging but we are still having cool temps and the potential for freezes. Usually temps down to about 29 or 30 for a short period of time are no big deal. We usually get our coldest temps early in the morning and they don't last long. If we were to get a hard freeze, say down to 25, then the time the temps stay below freezing is extended and we risk some damage. There is also the issue of moisture content of the air, where if we get a high humidity situation with fog and then hard freezing temps with the frost onthe buds and leaves it is more problematic. Last year I lost early leaves on my Akaji nishiki, Beni tsukasa, Kotohime, and Yezo nishiki, with some minimal frost damage on some other maples. This was a hard freeze with frost in late march or early april where you look out and the yard is covered in white frost. What I have been doing this year, which I can no longer do as too many trees have leaves unfolding is if I expect to drop below 30, I will take the plants to the garage. I did this about 5 nights in the last two weeks. Now there are just too many and the temps are supposed to be above 30 or 32 for the next week or so. After that, if I knew a hard freeze was coming, I might try to protect the most tenter. Early tender-leaf plants like Corallinum, Beni tsukasa, Beni hime, variegated dissectums--those sorts of plants. I hope that helps, but some of it you just have to learn from experience in your climate. My biggest problem is some plants that have come to me from greenhouses this spring or warmer climates that were well into budswell when they got here. That puts them about 2 weeks ahead of most of my plants and while the winter was mild, the plants are still not ready to leaf out. Sometimes the shelter of a porch or carport, as well as being close to the house can be enough to raise the temps a degree or two or prevent frost on the leaves. Here are a couple of photos of what the last week of winter/spring has been like here! March weather is always full of excitement and surprises. Kotohime 3/06/06, Aoba jo 3/12/06, and inbetween, SNOW (a rarity in southern Oregon) 3/10/06.
I had hundreds growing and then I went to 28 degrees. It depends on how many days they are leafed-out to figure freeze damage and what variety it is. I had little damage on ones that had leaves out 2 weeks or more. If a leaf is a week old it got damaged. Ones in sunlight were damaged more than ones more under large deciduous trees. It's hard to figure what is going to be damaged. In flats of new grafts some were damaged while 2 inches away there was no damage. Generally the red ones were more damaged and the ones in more sun.
Well, I've been lucky so far. After a very mild winter, we've had a number of nights recently with temps dipping down the high 20s and none of my Japanese maples has suffered any damage. I did move a few of them into my garage one night when the temps were supposed to drop as low as mid-20s, but it didn't get as cold as expected. Most of my maples have started leafing out, and a few have several inches of new growth already -- notably Koto no ito (6" of new growth), Garnet (1-2"), Acontium (1-2") and Villa taranto (1-2"). Some of my hostas haven't fared so well and had new leaves that froze.
