Protect from "freeze-thaw" and excessive moisture
Any container that contains lily bulbs needs to be insulated from rapid freezing and thawing. Failure to do so may result in rotted bulbs over winter. Although your bulbs can be perfectly hardy in the garden where ground temperatures fall and rise slowly over many days, unprotected pots can freeze solid within one hour. Surround the containers in sawdust or hay after the ground freezes, place them in a root cellar, or move to an unheated garage for the winter. Do not bury the pots in the ground for they will not be able to drain excess water properly, especially in early spring; the drain holes will rapidly become plugged and the pots will act as a sump, catching, rather than draining away, excess moisture.
Uncover or take your potted bulbs outdoors after danger of heavy frost is past. A few days of freezing temperatures will not harm the emerging sprouts in pots any more than it would harm emerging sprouts in the garden. It is the sudden and deep freeze/thaw cycles that cause damage. If potted lilies are caught outdoors without protection, and have frozen solid, try keep them frozen with mulch or insulation, for the winter, allowing pots to naturally thaw slowly in spring.
In the Pacific Northwest, winter comes and goes;we might be sunny and warm one day and frozen the next, with rain, sleet, snow or hail in between. The most important thing to avoid with our varying weather patterns both here and across the USA, is to not allow containerized lily bulbs to become saturated in their pots. Simply placing pots under an overhang, deck or covered porch, out of direct sun, is sufficient for most areas that rarely go below 15 degrees F. in winter. Placing pots on their side on the north side of a shed or garage also works rather well to keep off winter rain in milder climates, just remember to set them upright when sprouts emerge. Please remember that our guarantee for winter hardiness does not cover potted lilies, so be sure to protect your lovely lilies over winter or transplant them into the garden this fall.
Lily bulbs received in spring make the best potted lilies as they will naturally be shorter the first summer and anytime after bloom, can be slid out of their containers and garden-planted. However, the advantage to containerizing bulbs in fall in southern climates or for those gardeners with greenhouses (even unheated), is that you will naturally get a jump-start on blooming. Spring planted bulbs generally bloom about 10 to 14 days later than established bulbs. Containerized bulbs are usually earlier than normal, given that pots heat up faster in spring, and may bloom two weeks before the same cultivar planted in the garden. Mild frosts do not harm newly emerging lily spouts, but if a wild temperature swing is expected, move the containers under cover for the night.