The peace lily (Spathiphyllum) is a houseplant that produces attractive white flowers throughout the year and thrives in shade, making it simple to grow indoors. Peace lilies typically grow to about 16 inches in height, but large varieties can be as tall as 6 feet. In addition to adding some color to indoor spaces, NASA studies have shown the peace lily to be an excellent indoor air purifier, removing benzene, carbon monoxide and formaldehyde from the air. Though they are generally easy to care for, there are a few issues that can cause the leaves of a peace lily to discolor and turn brown, either at the tips or over the entire leaf. Fortunately, all of these problems have straightforward fixes and can be identified with a bit of experimentation.
Check the Water Level
Too much and too little water can both cause the leaves of the peace lily to turn brown. To determine which issue you are dealing with, dig into the soil up to your second knuckle and pull some of the soil out of the pot. Try rolling it into a ball. If you can't form a ball, the soil is too dry. If you can form a ball, squeeze it; if you can make water drip from it, the soil is too wet. Withhold water for a few days if the soil is too wet and water more frequently if it is too dry. If your soil forms a firm ball that won't drip water, your peace lily likely has a problem unrelated to watering.
Find Some Shade
Shade-loving peace lilies will usually tolerate bright rooms but not direct sunlight. Too much light will cause the leaves of these plants to scorch and turn brown. If your peace lily has brown leaves, move it to a shadier spot, preferably in a room that faces east or north. If this has solved the problem, your plant's new leaves will emerge green and remain that color.
The ideal way to fertilize a peace lily is to feed it a general 20-20-20 fertilizer once a month during the spring and summer. When doing so, it is best to dilute the fertilizer to one-half or one-quarter the fertilizer manufacturer's recommended strength. Failure to do so may result in over-fertilization, which will cause the leaves of the plant to turn brown. If you fear you have over-fertilized, flush the plant with water and stop fertilizing until the plant recovers. To avoid the potential for overwatering, you can instead transplant the lily into a new pot with fresh potting soil that has not been fertilized.
Remove the Damage
No matter what has caused your lily's leaves to turn brown, you'll need to remove the damaged portions of the plant to improve its appearance. To do so, follow the leaf stem of brown leaves down to the base of the plant and cut them off at their origin. As always, use sharp shears or a knife that has been sterilized to prevent spreading diseases from one plant to another. To sterilize your tools, soak them for 5 minutes in a solution of 1 part bleach and 3 parts water.