Let the flower stem die back naturally in fall. After the ground freezes, cover the soil with a 4"-5" layer of mulch. If you only have a few lilies, you can with good result invert a large container upside-down over the lily planting location and fill it with mulching material.

If you planted your lilies in well draining soil and have planted them at the recommended dept (8-10" deep) then you can probably even do with a normal 2-3" layer of mulch in winter without adding any more.

In spring, remove most of the mulch (leaving a 1-3" layer for regular summer mulching). Leave the bulbs in the ground. Do not lift them.

I have 2 Oriental lilies that are in a container. They haven't flowered yet, but there are many healthy looking buds. This is my first experience with any type of lily. First question - Will the buds open this late in the season ? #2 - What do I do with the plants in the winter ?
Thank you.