I'd pot them on and on milder days pop them out but in if frost/snow forecast. In other words harden them off. They are pretty tough plants.

I agree, they are very hardy when growing in the garden but best not to give them a shock.

Personally I would put them in the bin, They are the most awful thugs. We spent 20 years failing to remove them from our last garden where they were taking over the border.
Be warned.

some of the newer varieties are less of a thug, so depends on which ones you got.

I keep them in pots. I wouldn't want to be without them. There are also some nice dwarf varieties to be had. I've got one which doesn't spread at all, just stays as one clump all the time ... can't remember it's name now.

I'm sorry but I agree with OB. I planted several varieties in my garden and many years later I'm still trying to get rid of. Perhaps keep them in the original pots and give them away in the springtime!

Wow! Scary! Well, these are supposed to be newer varieties, but I have taken note and will keep them in pots! Thanks for all replies!

In my humble experience it is only the pink ones which spread, sometimes out of control. My white ones (gorgeous) stay exactly where they are planted.
Good luck Penny!

Gosh Sheila, I had a white one that I just could not get rid of.

I imagine how well they establish in the garden depends on the soil and site, my experience of thug plants has led me to plant in pots anything new that I feel may exceed its allotted space and sink the pot in the soil. Obviously the pot has to be deep enough for the roots not to escape through the drainage holes in the bottom, I speak from experience :-) I find this a way of coping with plants that need lifting too, like dahlias and others that grow from tubers, corms, bulbs etc. I overwinter these in the greenhouse, back lobby or front porch.
My Japanese Anemones have been well behaved but that may be because they are growing in clay soil, rather claggy when wet and jolly hard when dry!