I've grown calla lilies in pots for 3-4 years. The first year or two they were very beautiful with bright deep pink colors. Last year their colors started to fade a little and this year they are almost white with only light pink edges. I lived in zone 7 and recently moved to zone 9. I put my pots on the deck in spring and bring them in the garage in late fall. I didn't fertilize them last year and just started a few weeks ago this year. Is that the reason why they are fading?

Please help. Thank you.