My tropical hibiscus laugh at 40'sF. If its going back up in the daytime then they should be fine as long as its not too prolonged. You could throw a few sheets over them at night if you're worried. When it actually froze here last weekend I moved mine into the greenhouse.

If you freeze there you might have to move them into the bath tubs or something overnight. Some people string up the old school xmas lights on their plants for more warmth.

I have 3 in the ground and they actually appear to be loving the cooler weather.

Decorate them in christmas lights...not the led ones but the ones that produce a little heat . If it dips below 32° then throw an old sheet of blanket over them including covering the pot if they are potted.

Thanks so much for the advice. They seem to be liking the cooler weather, but was getting myself worked up about the over night lows. This is my first winter as a hibiscus mom.

Mine are all in the ground and bloom their heads off. Never been damaged by the cold, even in the 30's.

I wouldn't worry at all.

Jane