>>513589541
I used to wrap my fruit trees with a few layers of burlap but haven't done it the past few years. I think it's better to just treat the soil so it drains properly and the roots are deep enough to not die in frost.
Years ago I read about this guy who lined his garden box with black soda bottles filled with water, he argued that they'd heat up during the day and slowly release the warmth through the night. I always wondered if it'd work but I'd rather not use plastic.