Is it advisable to plant bearded iris in february
everything is better in the ground than in a pot but I wouldn't plant into frozen ground or a muddy puddle.
If it's bare root I would probably pot it up and protect it from wet.
I had misplaced some rhizomes which I have since found
I was just wondering if I could pot them up now
Plants need to have soil or compost round them. There is no point in a plant's natural life when the roots are exposed to air.
They won't survive if they're out of soil, as nut says. Pot them up, keeping the bulk of the rhizome clear of the soil, and water them in. Keep them somewhere out of the wind and weather for now if there's any foliage as they'll be a bit unstable till they get their roots down and established. You can cut any foliage back by half too, which will also help.
Then cross your fingers and pray a bit....