You could grow them on in the pot. The cold won't worry them, but they need some moisture in the soil - well drained, not wet. When I pot mine, i mix in that silicone jelly stuff that holds water, and some coir peat. Some osmocote fertiliser might be a good idea too.
I would sit the pot in a shallow tray of water, so that there is some percolation of water up into the soil.
Have they actually increased yet, or are they all single plants? They are surprisingly robust. I planted 3 seedlings out last year, and expected to say goodbye to them. They are clumps this year, of up to 12 rhizomes.
I still think they would be safer well cared for in a pot.

I started from seed about 5 years ago, since then I've given & traded away quite a bit & still have 3 large clumps. They multiply really fast, almost like weeds.

So they should be ok just left outside in the pot as long as I water them once in a while. Will they die back to the ground/dirt after the 1st freeze or will they do kind a like a regular iris?

Thanks for both of you replying. I think the one's I planted are purple and yellow. I planted some in two different pots. The other seeds did not come up. I don't know if they were old or if they didn't have enough cold storage before planting.

Marian

Marian, mine do die back, I think it takes a hard freeze though. I think if you put them in the ground now, they will be ok. When I grew mine, I planted them in the spring after frost. They are very hardy, & since you are a zone warmer than me, should be fine.

Thanks Nancy, I just hate growing something and not knowing how to take care of it. It would be terrible to lose them because of my neglect. I'm just learning how to grow alot of things from seeds. I am having a ball when something actually comes up. Today I planted some daylily seeds that I gathered off one of my daylilies earlier in the year. The seeds have been in the ice box so it will be interesting to see if I can get them to sprout.

Thanks for all you help.
Marian