Frosts are coming - will my tubs survive?

I have planted up some tubs of various heathers and a bit of thyme, most of which are flowering just now. They've done surprisingly well and I'm delighted with them, so the thought of them freezing as winter comes is pretty dire!

When I say it gets frosty here, I mean -10 and colder sometimes. Should I move them into stone tubs, or into the ground? Are they doomed regardless? :eek:

 

Skelf not too sure about thyme, heathers are definatly standing frost, after all Scotland is full of them. Always more of a problem of drying out in tubs, just watch this,if you really want to play safe for thyme,perhaps put some straw or loose peat over them, for winter...or move it in frost free position...for worst weather, if you get snow, that will protect too...so leave well alone then. Nature will then take care of it.

Ladybird

 

Another ruse is to move them closer to the building into a sheltered spot, if poss. Even in winter there is a storage heater effect which will make this area a few degrees warmer than out in the garden.

My thyme has been covered with snow several winters now, though, and doesn't look any the worse for it!