Answer: Browning leaves is often a sign of overwatering, but with peace lilies, as you might know, it's a little harder to diagnose. You can't let them dry out--if you do, they will wilt dramatically--they will collapse to the floor and look dead. Another possibility is salt burn. Salts in the water and in fertilizer build up over time. Browning usually occurs on the old leaves first. This excess salt accumulates in the leaf edges, where it kills the tissue and the leaf dries out and turns brown. It's important to water deeply and slowly. At least once a month, water deeply enough to "leach" or push salts well below the root zone. Frequent, light "sprinklings" allow salts to accumulate in the top layers of soil, where the roots are, which is bad news. Similar symptoms occur when too much fertilizer has been applied. Always water plants thoroughly before and after applying fertilizer to help prevent burn. Also, if plants are in too much direct sunlight, foliage can yellow and then turn brown, as it is basically "burning." I'd start by flushing your plant with water under a hose or faucet and let the water run out the bottom to leach away possible salts. Then examine the plant's environment for appropriate lighting and watering. I'd hold off on fertilizer for a month to see if there's any improvement. Fertilizer "forces" a plant to grow, which can be stressful if the plant isn't healthy. When you do fertilize, use a fertilizer higher in phosphorous (the middle number) to promote bloom.
Hope this information helps!
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