Improve poor or sandy soil by working in about 2 to 3 inches of an all-purpose potting mix. Use a trowel to gently dig up the ground near the base of the plant. Add the potting soil and mix it in. If your rain lily is in a pot, gently dig up the bulb and improve the soil before re-planting it. When re-planting the bulb, cover the entire bulb with at least twice as much soil as the bulb's height.
Add about 1 to 2 inches of mulch to the base of the plant once during the growing season.
Water your rain lily once a week during the spring and summer, unless you have regular rainfall. Drench the soil with warm tap water. The soil should become only moderately dry between waterings during the growing season. If it becomes too dry, water more frequently than once per week.
Prepare your rain lily for the winter by covering the bulb with about 3 to 4 inches of mulch.
Reduce watering during the fall and winter by about half the amount and frequency of previous waterings.