A boat lily plant grown outdoors tolerates most light conditions, but prefers partial sun. It also tolerates full shade, but this might slow its growth and lead to fewer flowers. When grown indoors, the plant prefers medium to bright light, such as on the windowsill of a lightly curtained west- or south-facing window.
Although the boat lily is quite tolerant of dry conditions once established, it's best to water a new plant in the garden whenever the soil's surface feels dry to the touch. Adding a 2- to 3-inch layer of bark mulch under the plant also helps conserve soil moisture and promotes new roots, but keep mulch back a few inches from the plant's center to discourage fungal diseases.
For a houseplant, provide regular water, usually once every week or two, or whenever the soil feels dry to the touch. After watering, allow the pot to drain well and never leave it in a water-filled saucer.
Although boat lily doesn't require fertilizer, you can boost growth by fertilizing it before you see new growth each spring. Use a general-purpose, balanced formula, such as 20-20-20, diluted at a rate of 1/2 teaspoon in 1 gallon of water, but also check the label for further directions. Use the fertilizer solution in place of a regular watering.