Ask Mr. Smarty Plants

We found many websites on this subject, and selected this one from The University of Georgia Agricultual and Environmental Sciences Department, because that is closer to South Carolina than some of the sites we visited. To begin with, weird weather or not, an overnight freeze in the middle of April is not going to last long, at least not in the Southern United States. The main problem with freezing temperatures when plants are already up and actively growing is that if the roots are frozen, it will cut off the water supply to the leaves and the plant will die. If the plants you are worried about are in pots, and especially hanging baskets, the roots are more exposed and we suggest you bring them in-into the kitchen or a garage. If that is not possible, put them on the ground and pile mulch or even dirt up around the plant roots. Just a degree or two of protection will probably save the plant. Water the container plants before you heap the mulch, etc. around them.

For actively growing plants in the ground, remember they have the best insulation there is, the Earth. Only very cold locations in North America are subject to freezing of the soil, and that only in protracted cold weather. However, just as you did the container plants, it would be a good idea to water them. Not a soaking, but just a nice sprinkle, a drink of water before the sun goes down. We don't recommend putting plastic or other sorts of freeze covers on those plants because they can break fragile stems and if you don't get them off quickly, they will be cut off from the sun, which they will need on the morning after a cold night.

Here is a previous Smarty Plants answer on protection of the roots of woody plants.