Do I need to remove the lilies after they have bloomed?
When lily petals deterioratel, it is a good idea to dead-head the remains of the blossom. This is true of all bulbs. Your hope is that the plant will focus its energies on re-building the bulb for next year's blooms instead of on making seeds. Your lilies may be able to do both or you may end up with fewer blooms next year if you don't dead-head.