Harry, if these plants have established themselves in the pots.....you can just bury the pots in somewhere in your garden till spring. I have done this with several kinds of plants, including roses and they came through fine for me.

I don't know about an unheated garage. It wouldn't work for me here in zone 2.

Sierra

I wouldn't risk leaving them in a garage. Sinking the pots would be better. But if you're going to the trouble to sink the pots, why not just go ahead and plant them if you've planned out the spot for them anyway. It's not too late and they're incredibly tough - I left some exposed in a pile in the garden over a northern MN winter. They all survived and bloomed without missing a beat.