Hi Teresa. I have some in pots too. I don't usually fertilize them over the winter. If they were planted in a potting mix, or fertilized when potted then they should have plenty of nutrients.
About a month before bloom time is when they recommend you fertilize the planted iris. You could give the pots some at this time too. Just be careful to not get the fertilizer on the rhizome. Mix it gently in around the outer edges of the pot perhaps. I would go with a light application.
Hopefully others will also chime in with some advice.
