Yes, if they need it.

No, not unless they really need it!
I am having this conundrum at the moment, Bamboo and Jutie. Long term dry weather but -3 temperatures at night. I keep a close eye on the forcasts on my computer and if they suggest we are going to have a few days when it does not freeze at night then I give my pots a good watering. Fingers crossed, it will not freeze for a couple of nights after watering.

Thanks guys

Yes, only if they need it, and probably best to water fairly sparingly and in the morning.

Agree with Steragram's comments, but bear in mind that a bit of frost is not usually enough for the entire compost/root contents of a pot to freeze. Very small pots may freeze solid at -5 deg. C overnight, but anything of a reasonable size won't. The real problem is if daytime temperatures don't rise above freezing, particularly for more than 5 days at a time.

Great advice for me too. Something I've also wondered about. So thanks to Jutie for asking and to Bamboo, Stera and Bulba.

Thanks again everyone, the temp is picking up during the day, and the sun is shining!!!!... Spring is here at last in beautiful Donegal!!!... (Although still frost at nite!)