Wiser rosarians than I have stated that a light and brief freeze doesn't present much of a threat to roses...however, I went out and watered all of mine lightly, because we had WIND all day long, howling wind that blew the birds out of the trees and stressed all the plants' new growth. Now we have a clear sky, with temperatures dropping like a stone. Oh joy. Where is global warming when you want some??
Laura

If it will probably stay above 28, I wouldn't. Covering usually causes some damage.