Lily bulbs are summer-blooming flowers. They are planted in late spring, after the danger of frost has passed, and in all but the warmest climates should be removed from the soil when the cold weather of fall arrives. Lily bulbs, like all summer-flowering bulbs, should be stored in a cool, dry location through the winter. This is the opposite of spring-flowering bulbs, which should be left in the ground during the winter, as they need to cold weather to start their internal "clock".
Lilies lie dormant during the winter, storing up their food for the spring. The roots, which are located on the bottom of the tear-drop shaped bulb, may grow somewhat dry, but the stem, which is located at the tip of the bulb, will not grow at all while in storage. Lily bulbs that are left in the ground during the winter will, over time, develop new bulbs.
Tiny bulbs may grow along the underground portion of the stem, and larger bulbs may develop from the original bulb. Simply remove the bulb and separate the smaller bulbs from it, and you will have new lily bulbs to plant.
Plant lily bulbs in late spring. Exactly when to plant these bulbs depends on both your local climate and the variety of lily you are planting, but in general, May is a good month. How deep you plant them, and in what location, depends on your type of bulb. In general, most lily bulbs are planted in partial shade, and around six inches deep. No lily should ever be planted in soggy, wet areas as this can lead to bulb rot.
Once the bulbs have been planted, fertilized and watered, they will start to grow almost immediately. Their leaves and flowers will start to develop within the bulb, and the roots will grown down into the ground. Shortly after that (about a week), the stem will begin to grow.
Once the stem reaches the surface of the soil, it will stop if it detects temperatures that are too cold. Once the soil has warmed up (usually after the danger of the last frost as passed), the stem will continue to grow, quickly pushing above the soil. Leaves will appear, and the stem and leaves will grow until the lily is at flowering height. Finally, the lily will bloom.
Lilies bloom only once, and then they wither. The leaves and stem will slowly turn yellow, then brown as the food stored in the leaves is sent back to the bulb. Without this food, the bulb cannot prepare a new flower. For that reason, lilies should be left alone until the flower, stem and leaves have completely died down to the ground. The stem will naturally separate from the bulb. After this happens, remove the bulb from the ground, and store during the winter.