Lilies should be fertilized lightly both before and after blooming to keep the bulbs vigorous. The authors of 1001 Hints and Tips For Your Garden recommend feeding lilies in spring just as the bulb's nose appears (the asparagus-like shoot) by scratching in a scant tablespoon of low-nitrogen fertilizer (5-10-10) around each plant and watering it in; the lilies should be given another light supplementary feeding at bloom time.
After lilies have bloomed, they need to be deadheaded, unless you want to collect the seed. Cut the stem right under the blooms, leaving the stalk until it withers. Once the stalks have turned brown, cut them off at ground level. It's best to dispose of lily debris off-site; as Edward McRae explains, this is the best defense against blight disease (Botrytis elliptica). The spores of this disease overwinter in the old foliage and stems and can rise to infect the young lily shoots during warm and moist weather the following spring, so make sure that you rake up and remove any old leaves as well.
Other than these few chores, you can leave your lilies alone. They won't need to be divided unless they become overcrowded, and will bloom happily for years.
Caring for Lilies in Pots
If you, like so many other gardeners, like to grow lilies in pots to brighten up your deck or patio, be kind to them in winter. Put your potted lilies in a building of some kind to protect them from frost; below zero conditions will kill them.
Your potted lilies will also need to be protected from excessive rains here on the West Coast. As Edward McRae of Cebeco Lilies points out, lily bulbs remaining in pots and containers over winter must never be saturated with moisture from winter rains. They must, therefore, be protected by an outdoor building, or a structure that protects from rain. The soil must be kept moist over winter, a slightly dry condition being preferable.
If you're going to pot lilies, fall is the season to do it. Put a one inch layer of a mix of two parts potting soil to one part vermiculite in the bottom of the pot and set the lily bulbs on top, making sure they're not touching each other. After filling the pot with soil, store it in a cool place where the bulbs won't freeze. In spring, move your pots out into the sun (1001 Hints and Tips For Your Garden).
