I left my Japanese maples in pots outside all winter last year with no problems, but the coldest temperatures we got were about 20 degrees F. It's supposed to get down to about 15F over the next few nights, with lower temps in some areas. Just wondering if I should bother moving them into my garage for a few days. They've been outside all winter so far, with lowest temps so far in low 20s.
Mature roots of Acer palmatum 'Atropurpureum' have been known to be killed by 14F/-10C. Immature roots of same plant will be much less hardy. For example, Magnolia stellata has been noted losing immature roots to 21.2F/-6C and mature roots to 8.6F/-13C. The same species can vary, M. stellata has also been recorded losing mature roots to 23F/-5C. When the mature roots go you've lost the whole plant. Loss of immature roots manifests as stunted top growth the following spring.
Sounds like I better start moving some pots this afternoon. They're forecasting a low of 12 on Monday.
My potted maples stay outdoors without any protection and, down to temperatures -10°C/14°F, I have not noticed any damage. Maybe some roots suffered but I have not seen any serious plant loss or stunted growth. Gomero
Better safe than sorry. It wasn't too much trouble moving my maples into my garage. I've got about a dozen of them in containers, mostly 1-3 gallon size. My garage is unheated so there shouldn't be a problem with it being too warm either.