I know that small potted Trachys (such as 12” high) can get “root-frozen” at temperatures much higher than ground-planted Trachys. I used to know this Rule-of-Thumb number in degrees F. but cannot recall it now. Who has some guidance/advice?

I had a palm expert relatedly advise that placing such potted Trachys under a mature Magnolia (as opposed to having the plants in an open field) can create some partial protection of a few degrees by reducing the immediate temperature drop by a bit.

My situation is I don’t have a garage and my small greenhouse is already pretty filled up. I’d hate to lose the potted Trachys but would rather not “bring them in” unless my inactivity might prove fatal for them.

Thanks for any guidance.