As we get ever closer to winter I wonder if any Nuts have ideas for warming beds for your trees.
I've not used them in the past but have acquired a number of tropicals this year.
Any ideas appreciated.
Tropicals should be indoors. Different species will die at different levels of cold temperature. I only have a few, but they come in when there is any chance of frost, or even temps in the 40s. For their health, BTW, you can completely defoliate ficus microcarpa before bringing it in, and if you want to you can do it again in the spring before putting it out. That will not only give it the health and stylistic benefits of defoliation, but also when the leaves come out again they will naturally acclimate to the "weather", indoors or out, rather than going through some sort of shock.
Semi-tropicals like Chinese elm - many varieties of which are VERY hardy for semi-tropicals, BTW - can be wintered in an unheated garage, but I don't know how certainly you can expect them to survive intact merely mulched in in a cold frame, given the severity of the winters you have there. A warming bed, therefore SOUNDS like a good idea, but I'm not sure of the practicalities of setting one up given the fact that regulating the overall temperature might be tricky. You'd essentially be setting up a little greenhouse, and that can be tricky in its own right. If you merely use a warming pad under the pot, without a cold frame around the tree, some Chinese elm can easily lose major branches or simply die during a cold snap or extended cold. You might look up my post from several months ago here on the Chinese elm that partially survived my three winters in Taos, NM. Granted, the extreme and rapid winter temperature shifts of that local would be unlikely in your climate, but I still would use an unheated garage there for Chinese elm. CE can also winter indoors as well, but they lose vigor and just look rather pasty, rather than vibrant, if allowed to do this year after year.
Hope that helps.