Popular as a potted plant in dimly lit areas of the office or house, peace lily (Spathiphyllum spp.) grows best in warm, humid locations with an evenly moist soil. Drafts, frost and improper watering leads to sickly or dead foliage.
Black leaves on a peace lily most likely result from overwatering. This causes roots to suffocate and rot. A container resting in water in a saucer basin leads to rotting roots, which quickly manifests as sagging, black leaves and stems.
People not blessed with a green fingers usually assume wilting, yellow or black leaves only means the plant is "thirsty." They water the peace lily again, exacerbating the problem.
Water the peace lily once the top 1-inch depth of soil feels dry to the touch. Then, use room-temperature water, not cold water. Empty out water from the bottom saucers within 15 minutes to keep the roots from lacking oxygen and starting to rot.