Hi, do you mean the true Calla lily, or a species of Zantedeschia, or arum lily, both are marginal aquatics, but can be grown in reliably moist soil, but the true calla's are fully hardy, whereas most Zantedeschia's are'nt, but that doesn't really matter, in relation to the question, neither of them flower more than once a year, but the Calla's produce berries in autumn, Zantedeschia's don't, Derek.

If the spathe was pink to begin with, it was likely a Zantedeschia rehmanii, or one of its hybrids, and they're not any kind of water plant. The pink callas, as well as the yellow, orange, and purple kinds, are subtropical rhizomes that need moderate summer temperatures, good drainage, and no frost. They only bloom once in late spring or summer, then gradually go dormant. The rhizomes can be stored in the winter like Dahlia tubers.

It seems I've been very lucky that the pink flowers have lasted until August then. Also, that they survived the winter in a pot (although we didn't have a hard winter where frost is concerned). Thank you both for your replies, very much appreciated.