Looking out to see a very frosty garden this morning I was reminded of a tip that I heard many years ago from one of the staff at the Australian National Botanic Gardens. While many plants can cope with frosts (down to -5 degrees) one of the main reasons plants die following a frost is actually due to water stress.
Sounds weird, but what is happening, particularly in a dry winter like we are currently having, is that as the temperature rises during the day there is insufficient water for the plant to access and it wilts due to lack of water. Now I know to us the daytime temperature is not that high, but on a day like today where our overnight temperature is several degrees below zero and our daytime temperature is 13 or 14 degrees you can have up to 20 degrees difference in the temperature. So you can see that you plant might well need some water to help it cope.
Best plan is to water as early as you can in the day, (depending on how quickly your hose thaws out!), focussing on those areas of the garden where the soil is dry. While I don’t think you need to go as far as one garden writer I read recently who suggested that you water your lemon trees with tepid water in winter, keeping an eye on how dry your garden is getting may well help save some valued plants.