Go ahead and enjoy your plant inside until it is done blooming. Then, place outside in a well protected warm spot that still gets a good amount of sun--preferably up against a southern wall. Even though the temps may go below freezing at night, it takes quite a bit to totally freeze the plant. Keep it there until the stem itself turns brown. In the meantime, dig a shallow trench in a well drained area of your garden, deep enough so you can lay these pots sideways in it, and leave open. Save the top soil you dig out and store in buckets in the garage. After the stems turn brown, cut off, leaving about two inches of stub. Then, place pots sideways in the trench, cover with saved unfrozen soil and water in--even if the soil in the trench is frozen, it doesn't matter--it will re-thaw enough to settle in. Mulch lightly a couple weeks later if you think they need it. What I usually do if the ground is not yet frozen, is to mound a couple more spades of dirt over the top and then smooth it over to form somewhat of a mound. So, enjoy your lilies and sleep well. This really works great and when you dig up in the spring you can either continue to grow them in pots or plant in the garden! As long as they get the in ground winter chill, you'll have flowers, too
