Peace lilies (Spathiphyllum spp.) grace indoor spaces with their glossy evergreen foliage and creamy white flowers blooming throughout the year. Though they're considered low-maintenance plants with few problems, poor cultural conditions and practices can lead to black foliage. The good news is, you can often fix the problem with proper care.
Peace Lily Culture
Preferring warm, humid, tropical conditions, peace lilies may be grown outdoors in U.S. Department of Agriculture plant hardiness zones 11 through 12. If you live in a cooler region, grow them indoors year-round or outdoors in a container that you can bring inside when cold weather threatens. Peace lilies favor bright, filtered light and are unusual because they flower in the lower light levels found indoors. If you're growing peace lilies outdoors, place them in a partially to fully shaded area to prevent leaf burn.
Too Much Water
Peace lilies like their soil consistently moist, but this doesn't mean they'll cotton to constant sogginess, which can cause their foliage to turn black and may also lead to root rot. To head off these problems,
- Use containers with drainage holes in the bottom.
- Grow peace lilies in rich soil that drains well.
- Use room temperature water when irrigating the plants as their roots are sensitive to cold water.
- Prevent burn injuries by letting tap water sit at least overnight before watering to allow chlorine to dissipate.
- Avoid using softened water, which may contain high levels of sodium.
- Water the plants approximately once a week during the growing season or whenever the top inch of soil feels dry.
- Saturate the soil until water runs from the bottom of each container, which ensures that the entire root system receives moisture.
- Empty each container's overflow tray after watering to keep the roots from sitting in water.
- Provide needed humidity by spritzing peace lily foliage with water once a week during the growing season.
- During winter, cut back on watering to about twice a month.
Too Much Fertilizer
Excessive use of fertilizers and improper watering of peace lilies can lead to a concentration of soluble salts in the soil, creating problems such as blackened foliage and leaf tips as well as burned roots. Peace lilies don't have high fertilizer requirements, so frequent fertilization isn't necessary or recommended. To leach or purge salts from peace lily soil, place each plant in its container in a sink or bathtub; then run fresh water through the container until it flows out the drainage holes. Repeat after letting the soil drain for about five minutes. Leach the soil approximately one month after applying fertilizer. Withhold any further fertilizer treatments until the plant recovers with healthy new foliage.
Proper Fertilization Practices
It's only necessary to fertilize peace lilies every two to three months during the growing season. Refrain from fertilizing them during the cold months of winter.
Place 1 teaspoon of 20-20-20 water-soluble houseplant fertilizer in a 1-gallon or larger watering can.
Fill the watering can with room temperature, nonchlorinated water and mix well.
Pour the mixture over the soil until it runs from the bottom of the container.
Peace lily foliage can also turn black when subjected to temperatures of 45 degrees Fahrenheit or lower. Keep the plants in a warm indoor environment with daytime temperatures between 68 and 85 F and nighttime temps approximately 10 degrees cooler. For best growth, place peace lilies in a north-facing window out of direct sunlight. If your region experiences frosts or freezes, bring outdoor peace lilies inside well before temperatures drop to 45 F.
Dealing With Damaged Foliage
Once a peace lily's foliage turns black, your only alternative is to trim it off -- it won't revert to its healthy, green color once it's damaged. To avoid spreading diseases to the plant, sterilize your pruning tool by wiping the blades with a clean, alcohol-soaked cloth and allowing them to air-dry before pruning. Then snip off the entire affected leaf and stem at the soil level.