Move potted plants close to the house; if possible avoid the north side since it tends to be cooler than other exposures. Protect very tender potted plants by housing them in a garage or shed over night.
Plants that can’t be moved can be covered with sheets or drop cloths; be certain the fabric doesn’t touch the foliage since the cold material can damage leaves. In the morning, when the sun comes out, remove the cover promptly.
If plants are harmed, do not prune away damaged foliage and branches; damaged portions may recover. Also pruning stimulates new growth that is extremely vulnerable to cold. Wait instead until spring, when temperatures moderate and new shoots can thrive.