I've done it before at this time of year. I suppose it depends a bit on where abouts you live, and the forecast for the rest of Feb is pretty cold!
However, with a spare black bin, I'd cover 1 or 2 or 3 of your crowns, (depending on how close they are), with the bin, and then insulate with compost/manure/bubble wrap held in place with chicken wire or something similar.