Zantedeschia are commonly called Arum lillies, and most are grown in greenhouses with a minimum winter temperature of 50 deg f, Zantedeschia aethiopica can be grown outside in mild areas, and the variety "crowborough" is borderline completely hardy, the ones grown in the greenhouse are usually evergreen kept just moist in winter, Derek.

I had 2 pots with some in last year and they survived! I didn't realise till I emptied the pots to replant with more to find the bulbs still looking remarkably happy!
I took off the babies and repotted them. Wish I hadn't as only my purple one flowered. All the rest just had leaves :-(