To be more specific and answer your question, after LAST frost I would put the pot outside. You are in zone 6 right? Keep in a sunny location, water well and after 1st frost follow previous advice. Here's what I include with bulbs I've given away or donated plant sales: Zantedeschia albomaculata: Calla Lily Form: Tender bulb. Exposure: Full Sun. Height: 24" (to 30" bloom). Spread: 18-24". Zone: 8-10. Flower Date: June-July. >Planting Reqs: Plant 4-8" deep and 18-24" apart when all danger of frost has passed (last week of May in ELong.). I plant those in back 4" deep and those in front 6-8" then cover all with 2" of compost/mulch. Fertilize using a 5-10-10 or 5-10-5 fertilizer. >Lifting Reqs: Lift the rhizomes after first frost, cut back stems, clean off excess soil, let dry out of the direct sun for a few days and then store in a dry location that remains between 50 and 60 degrees F. They can be divided before storage as long as the cut portions are allowed to dry. Doing so will prevent the open wounds from rotting. I use perlite in a PAPER bag. Check in late January. If rot is evident cut, scrape and clean off all rot. Coat cut surface liberally with powdered anti-fungal or cinnamon pushed firmly into flesh. Let dry and store. >Soil Reqs: Slightly acidic (6-6.5) well drained, humus enriched sandy loam. Adding mulch to the soil will help maintain a constant soil temperature. This will help keep the plant stress-free. Mulch will also improve the texture of the soil and help hold in valuable moisture. Calla lilies thrive in well-drained, loose soil. >Pruning: Remove spent flower stems to tidy up your plants and strengthen leaves and corm. >Note: Watch out for Japanese Beetles. Hope this helps. Evan

Oh, and a post script- Callas grown from seed take sometimes 2, but usually 3 years to build a big enough tuber base to want to flower. Don't be surprised when you just get leaf mass the first year. I typically grow mins in an aquaponic coconut coir grow bed indoors for almost a year under my favorite blend of T5HO aquarium bulbs (standard florescent grow bulbs are garbage) on a 24 hour light cycle to maximize growth, then dug up the bulbs up a few months before planting time to let them be dormant for a bit. That way, they always bloom when I put them in the ground.

Not really :-) And depending on where in the UK you are located, it might also be possible to grow these long term outside. Certainly the tall whites (Zantedeschia aethiopica) should be able to be grown there year round. IME, a great many flowering plants sold for indoor use are not intended for long term indoor use - mini roses, azaleas, hydrangeas, campanulas, callas, etc. are all sold more like long lasting cut flowers. If they cannot be transitioned to the outdoors (where they belong), then just toss after flowering is completed. Getting them to rebloom or even stay healthy under indoor conditions is best for those with glass conservatories :-) Or greenhouses.

if you have many.. just try it .. give it a week or so ... see what happens are they currently blooming ... where are you.. any chance at a pic .. so we can get a flavor of the situation?? ken