Japanese Black Pine Over-Winter

I remember Ryan saying that JBP cannot go below 25 degrees Fahrenheit or you risk damaging the roots. I live in Rhode Island and I am curious if any New England’s just bury the pot and leave them outside over winter? I know the air temp definitely gets below freezing but I am curious if the soil stays warm enough that the roots are OK. Of note these are prebonsai in nursery soil, not bonsai yet. Thank you for any advice!

I am in Spokane, WA (zone 5b) and put my Japanese Black Pines into the just above freezing greenhouse after they experience a frost or two. I have lost ones that were in the hoop house that gets much colder.

I live in Boston, MA and have one in a very small container so this goes inside large unheated cold frame buried in crushed marble. I have another in a pond basket that I just buried outside in a raised mulch bed it did fine. It is in a pond basket on a heat bed this winter because I had the space.

Unheated cold frame with pines in full sun in crushed marble.

I live in WI. I overwinter black pine inside a real greenhouse with heat as I find that you get faster development of the tree and they don’t seem to need a cold dormancy. I do put them in the far corners though where the temp can get down to high 30s at night when temps outside are less than zero. Gives me something to use that colder area of the greenhouse for.

Thanks for the advice all. I ended up deciding to put them in my unheated attic which drops below 40 but never freezes and has a window for light. We will see how they do.