That is one way. You don't want to break the small hair like roots. It is best to try to straighten the roots out, but if it means ripping off some of the air like roots, then just make cuts down the sides with a box cutter or some other sharp tool so they don't strangle each other.

Sue, when you take them out of the pots, if you find they've been containerized so long the roots are completely dense and matted, you can root prune them.

This is generally successful if you use a sharp knife, emphasis on sharp. Cut away 1/2" matted roots from the edges of the root ball of a 1 gal plant, 1" from plants in larger containers.

I'm surprised these are so rootbound. I bought them from a good garden center (not big box) near us, and they don't overwinter stuff (they close in the winter). Anyway, I'll have to see how bad they are when I get them out.

What type of a knife is used for root pruning?

I use a sturdy utility knife/box cutter or a flooring knife.

Thanks Rhodyman!