The blooms are large but last only about two weeks. You must leave the foliage in place after the blooms have fallen off. The bulbs need to rebuild their energy supply if you want them to come back next season.
  To increase the planting, buy more bulbs. You can purchase them from a mail order distributor or find them at a garden center. Lillies are one of the most common flowers given as gifts. They are often used by florists.

  You can also dig up the bulbs in fall when the foliage has died back and plant some bulbs in a new location. Be a little careful since the bulbs are not that difficult to damage. The small new bulbs may not bloom for a year or two. 

  You can extend the bloom season by planting different varieties of lilies or planting some lily bulbs in different locations with varying degrees of shade. Plants grown in sunnier spots will get an earlier start in the spring as the soil warms more quickly.