Perform a soil test in the fall to determine the pH of the soil in your garden. Crinum lily prefers a soil pH range between 6.0 and 7.2. Use a commercial soil test kit or consult your local cooperative extension service regarding soil testing. Amend the soil according to the test results. This might include incorporating limestone into the top 7 inches of soil to raise the pH or using sulfur to lower it.
Incorporate a 3- to 4-inch layer of organic matter such as peat or compost into the soil to promote drainage. Crinum lily requires well-drained soil, and poor drainage can result in diseases and bulb rot. At the same time, enhance nutrients by working in 3 pounds of a 5-10-5 fertilizer per 100 square feet of planting area. Unless rain is expected, water the soil immediately after fertilizing to soak the nutrients into the soil.
Dig a hole with a trowel in a full or partial sunny area of the garden. Place a crinum lily bulb in the hole, planting it at least 6 inches deep with the pointed side up. Planting the bulb deeper results in a larger bulb and fewer offsets. Space multiple bulbs 2 to 3 feet apart.
Water the soil immediately after planting, keeping it moist -- not wet -- throughout the growing season. Provide about 1 inch of water a week and adjust your watering after rainfall. After blooming, reduce your watering frequency, allowing the soil to dry out between watering.
Spread a 2-inch layer of bark chips on the soil around the plant to keep weeds at bay and to promote soil moisture retention. In cooler climates, use a 4-inch layer of mulch for extra protection from the cold.
Fertilize the soil in the planting area in spring and midsummer after the crinum lily establishes. Broadcast a 5-10-5 fertilizer over the soil at a rate of 3 pounds per 100 square feet. Water the soil after fertilizing to soak the nutrients into the soil.