I think I would go with white 5 gal buckets if you have some (and the plants are small enough) as the best choice because of light transmission. Otherwise 5 gal buckets of any color or cardboard boxes (it's dark inside but will protect better from the cold) I would hesitate to use cloth because if the shrubs have leafed out, they may be damaged from rubbing. If you have tomato cages, you could put that up then wrap with cloth.
I know -- they're predicting low 20's overnight around here with windchill down to 21 or something
I put my 3 potted rosemaries, one citrus, and a geranium basket outside already more than a week ago, and I'm going to have to scramble to bring them back inside.
My apples and other fruit trees broke bud already -- I hope they'll be alright....