Have you given it any fertilizer? My experience has been to keep them pretty well fed and they grow and flower for most of the summer.

Thanks Mvespa for the suggestion. No I hadn't given it any liquid fertilizer yet as I thought I should wait until there was more growth. But I will give it a try. In Mass, we've had cold, rainy weather and we've had to run the heat until recently. May be if I give it a little fertilizer and we have warmer temperatures it will grow. I guess I was discouraged that one of them rotted. I have always been fascinated with these plants and when I saw the bulbs I thought I'd give them a try without a big investment if they proved difficult to grow.

They aren't really hard to grow, but they don't like being houseplants. If you can, slowly move it into full sun outside, and you should be rewarded with flowers. Make sure you just don't take it outside and put it in the sun- the leaves with burn! (voice of experience here)
I just let mine sit until it is warm enough to plant outside, unless I see roots coming out of the tuber. I've had ones with green sprouts sitting the basement for several months. Once I take them outside and plant them, they will grow like crazy.
Susan

If the bulb was really small it might not flower this year but should award you with blooms next season for sure.

I also find that my callas don't bloom for aleast a month and a half to two months after planting the bulbs. They need time to really leaf out.

I would also agree with the suggestion of putting them outside in the sun (slowly at first).

I am happy to report since moving it outside and acclimating it to full sun and giving it some liquid fertilizer as suggested, my calla lily is sending up new growth. In Massachusetts, we are in the middle of a heat wave now and so the plants must be benefiting from the warm temperatures.

Thanks for all the advice!