Asiatic lilies are beautiful perennials that once planted, will bloom and multiply for many years with a minimal level of care. However, the bulbs must be planted in well-drained soil as Asiatic lilies won't tolerate wet feet, and can eventually rot. If you have poorly-draining clay soil, don't be discouraged. You can still plant lilies as long as you take the time to improve the soil's drainage capability first.
Spread 4 to 6 inches of organic material on top of the soil. Materials that can improve soil drainage include compost, well-rotted manure, finely shredded bark, straw, grass clippings or a combination.
Use a rototiller to work the organic material into the soil. Till the soil as deeply as possible, combining the native soil with the organic material.
Add a granular superphosphate fertilizer with ratio numbers such as 0-20-0 before planting the Asiatic lily bulbs. Apply approximately 3 pounds of fertilizer for every 50 square feet of planting space.The phosphate will encourage healthy blooms, and will give the lilies a boost in the clay soil. Repeat every two to three weeks until you can see the color of the lily buds. Be sure to work the fertilizer thoroughly into the soil, as fertilizer added to clay is more difficult to absorb.
Plant each bulb at a depth of approximately double the bulb's height. Plant Asiatic lilies between mid-October and mid-November.
Spread a 1 to 2-inch layer of organic mulch around the Asiatic lilies every spring. Mulch will keep the roots cool, and will help to deter weeds. Use a mulch such as straw or grass clippings, which will continue to improve the soil quality as it decomposes. Avoid piling mulch directly on the plants. A fresh layer of mulch in autumn will protect the lilies from the soil freezing and thawing.
Water the Asiatic lily bulbs three times per week during spring and summer. Allow the soil to become almost dry to the touch before the next watering. Shallow watering is better for plants in amended soil, as water often can't move easily from the amended soil to the clay soil.