I assumed that you grew these indoors. If so, I'd wait for the weather to be a little milder and I would gradually get them accustomed to growing outdoors by placing them in a cool lighted room in your home and planting after all danger of frost has passed. If these are true lilies, they should be hardy enough to grow and mature in the garden where they form a bulb that should bloom in 3-4 years.

Best of luck!

Riz

Ditto for the advice from Riz.

If these are growing in a container, harden them off like any spring transplant after last frost date. I keep the small seedlings in the container until they are a reasonable size to transplant later in the summer. You can then transplant so they get established before the fall, or keep them in the container and bring it in for protection over winter and transplant the next spring. If you have the room, you can grow them on under the lights.
Works for me.
Bonne chance!
K