I just leave them in the pots outside over winter and they grow and bloom next year even better. I am in zone 8B and they winter over with no problem. If I want more I will dig them up and divide so that each division has a part of the base and they will grow and bloom the next year. Al

Unlike many "bulbs", Lilies don't go completely dormant, so digging them up and storing them in a bag out of the soil should not be done. I've had Asiatic lilies in pots and they did fine for about 3 years provided I watched the watering when they weren't actively growing. Too much water in the winter leads to mush in the spring. What I would do is about mid September, just as it's cooling down a bit, unpot them, change out the potting soil and then replant them in the pot. This is the normal time in my area for planting them in the ground as it's still enough time for a root system to develop before winter sets in. In doubt about the timing you could always wait until early spring to repot them.

Minimum size container for oriental lilies seems to be 2 gallons and they appreciate a change of mix after two years (assuming you've top dressed them with compost and/or something like dry sheep manure pellets between changes.) They do like being fed.

If you have a lot of rain over the winter check early that your pots are free-draining and put them on pot feet. 'Damp - not drowned' for lilies.

Keep an eye out in early spring for the first slugs and snails. Fresh lily tips are nearly as yum! as Hostas...

Thanks everyone! I guess, I will leave them in pot and re-pot them in spring.