Any time the ground isn't frozen or totally waterlogged.

Hi, I agree with Mg, but if your ground is waterlogged or frozen, you will have to keep the roots moist until conditions improve, Derek.

Any time between now and late Feb when the ground isn't frosted over or saturated by rainfall. So a mild, dry spell in winter would be ideal.

I've had to put mine into large pots as when they were delivered the ground was frozen. They are in the shelter of the house wall and looking ok. so if you cant get them in pot them up in general purpose compost. That was the advice given on the instructions that came with my roses.