What do I do with trees in pots in this weather?

[franke]

I've got a couple of nice trees (Japanese acer and a Gingko Biloba) in large half barrels. How do I stop them from dying of thirst in this weather? Is giving them slightly warm water a really daft idea? It's -9° here tonight and sub-zero even during the day until after the weekend at least.

You might want to wrap fleeces around them now that it's frosty.

thanks both. I thought it might be a bit late in the day to be doing the fleece thing, but I suppose I've got nothing to lose now - I'll give it a go.