Are you growing these indoors?? Lilies are not really long term houseplants - rather more of a flowering gift plant when sold in a container in bud and bloom and intended only for a short term indoor enjoyment while that is happening and then either tossed or replanted outdoors. They just don't get the conditions they need to grow, thrive, return and flower properly if grown only indoors, unless a greenhouse is available.

If indoors I would move them outside now. They really need the benefit of all that proper outdoor growing provides - sunlight, proper temperatures, rainfall, soil nutrients, etc.

Ok, Thank you for your advice.

Yes I bought them last year and enjoyed them indoors because we lived in an apt. But now I will move them outside.

Should I wait till they have browned in the fall and transplant them then? Or can I do it after the last frost date here.

No need to wait for fall or last frost date. If your soil is workable, you can plant them now.