I'd wait for them to go dormant, and then plant them in late winter/early spring.

They are almost dormant. Have lost a lot of their leaves. And by late winter early spring the ground will be frozen.
I have them now 3 years in pots. So they are about 2 feet or so tall.

My ground never freezes so I've never had that problem, but you should have a lot more growth than that after 3 years. They're probably root bound and need to be in the ground, so either do it now, or wait until the ground thaws.

Gardenfreak wait till weather permits in spring.

If in pot for 3 years as you mention take sharp box cutter or knife and slice shallow from top to bottom 3 or 4 spaced out
cuts .
Then plant .

Martin