I bury mine about a foot. It keeps me from having to stake them.

Leave the ends of the long sprouts protruding above the ground. Lilies can pull themselves down with their roots so they will adjust the depth later. If the sprout is short, you can bury the bulb at the recommended depth (2-3 times the diameter of the bulb).

Thanks for your help!

Another question: Alina, re. the longer sprouts; if the sprouts are 3 inches, would you leave a quarter inch protruding? I am worried that a long sprout protrusion might break or not be able to develop into a strong stem. What do you think?

A quarter inch is OK. Another option is digging a deeper hole, but not covering the entire bulb+sprout at the planting time. You can add soil gradually later. Also, I would not worry about stronger stem now. Usually, Lilies are shorter their first year in the ground. I planted sprouted Lilies as late as in June. They were just fine. Lilies are tough. If deer will not eat them, you will see them blooming this year ;)

what about the little bulblets. Can these be planted on their own when dividing in spring?