I have 20 calla lily bulbs and they refuse to bloom (for 2 years now!). some are in clay pots, some in sun, some in part shade, some in rich loam in garden where the dahlias are 10 feet high covered in blossoms. I have fertilized some, and others not. beautiful leaves and not a bud in sight…
I was very happy to see your question, as I grow Callas myself and I was puzzled as to why flowers were a “no show” this season.
Callas are not actually lillies but a family of plants know as Zantedeschia. They grow not from bulbs, but from rhizomes which are a modified underground stem. They are relatively easy to grow, not needing any special soil and agreeable to many light conditions. But Callas do need to be kept moist, but not too moist as they can rot. Monthly applications of fertilizer can encourage flowering, but I suspect that your lack of blooms may be the result of overcrowding in your clay pots. Callas do need room to grow and expand their tentacle like roots. My suggestion would be that when you prepare to bring in your plants, first allow the leaves to die back, resist the temptation to cut these browning leaves off as they provide food for the following season. Then divide them up (possibly share with friends) into several pots for storage, or you can remove your rhizomes, shake off any soil, and store them in loose peat or coir. Repot in spring making sure that your plants have lots of room, and with regular fertilizing you should be rewarded with beautiful blooms. – That will be my game plan!
Best of luck