The genus Lilium contains over 100 naturally occurring species and many more hybrids that have been developed for commercial production and the home garden. Some members of this family can reach heights of nearly six feet, with the stunning trumpet-shaped flowers held at the top of the foliage. Most lilies bloom from late spring through the end of summer. Some common varieties include the Stargazer Lily, Lemon Lily, Rubrum Lily, Annunciation Lily, Royal lily, Casa Blanca Lily, Easter Lily and Bamboo Lily. As with many other bulbs, you must dig up and separate lilies in the fall---but not every year.
After your lilies have finished blooming, it's wise to dig them up and separate them periodically---some experts say to do this every three to five years, or when large clumps form at their base. September through October are the best months to undertake this gardening chore. Lilies also produce "bulbils," which are small bulblike structures that can form a new plant. Pinch these off in early fall and plant them in pots if you want to make more lily plants.
If didn't find the time to dig up and move your lilies in the fall, you can successfully move them in late winter or early spring. Dig up your bulbs as soon as you can work the ground and then plant them in pots that you place in a cool, dark place such as a root cellar. Make certain you keep the soil moist. When sprouts begin to appear and the weather warms up, move the pots outdoors or transplant your young lilies to an appropriate spot in your garden.
Because bulbs such as lilies require a period of winter chill, you can expect the best flower production in the spring if you plant or move your bulbs in the fall. If you plant them or move them in the spring, expect to get some flowers later in the year, but this blooming season will be shorter than for bulbs planted in the fall.
If you plant your lilies in a spot where they receive good air circulation, you can usually avoid the fungal disease botrytis, to which they can be prone. Also, set bulbs about six inches from each other---this will allow airflow between the plants' leaves, which will allow them to dry out more quickly. If brown spots begin to appear on lily leaves, especially during long spells of wet weather, you can treat your plants with a commercial fungicide, available at local nurseries.
Hints and Tips
Although lily bulbs are normally hardy, new growth can be nipped by frost. Cut off affected leaves and hope for warmer weather when the new growth appears.
Lilies are low-maintenance flowering plants that only need fertilizer if they grow in poor soil. Fertilize with a balanced fertilizer your nursery recommends for flowering bulbs---do this when you first see growth at the soil line. Repeat one month later, but do not apply fertilizer when plants are forming flowers.