Hi Johnp58, are you sure it's a Calla lily?, these are marginal aquatic plants, grown in water about 2-3 inches deep, and are fully hardy, if on the other hand you have a Zantedeschia, these can vary as to hardiness, some being very near to completely hardy, Zantedeschia aethiopica, right down to frost tender plants that need a minimum winter temp of round about 50 deg f, so there is quite a bit of difference, Derek.

Hello Derek.....I am sure it is a Calla Lily as it was given to me yesterday in a small pot and it as a label saying Calla Lily as it came from Morrisons...lol .....I have potted it up and will water it well and keep it in semi shade....it has three most beautiful deep red almost black flowets. When I took it out of the pot itwas almost pot bound with thick fleshy roots. Phil.

Hi Phil, have the leaves got white splashes on them? I'm almost certain that you have a zantedeschia, as there is only 1 species of Calla lily, which is the 1 I've described, but there are 8 species of Zantedeschia, and a lot of hybrids, 1 in particular, which seems to fit your description, is Zantedeschia schwarzwalder, which is a elliottiana hybrid, and has blackish maroon/purple spathes, and requires a minimum winter temperature of 50 deg f, so is probably best grown as a house plant.
Grow it in a loam based compost, ji no 2, water freely whilst it's in growth, in full light, but not direct sun, and feed every 2 weeks until the flowers have, and keep it just moist in winter.
It seems that a lot of plants get called Calla lilies, but are confused with Zantedeschia, which are Arum lilies, not least the people who produce plants for supermarkets, it seems anything with a spathe is a Calla .
Sorry that should have read, until the flowers have faded, Derek.

Thank you Derek....most helpful and whatna comprehensive answer. I am on holiday in Madeira right now for 2 weeks but the day before I left I re-potted the plant and watered it well and left it in the shade. i am sure, by how you describe them, it is a Zantedeschia. I am most gateful.