The peace lily, or Spathiphyllum, is a widely favored houseplant known for its graceful appearance. While generally resilient, the most common indicator that the plant is struggling is the yellowing of its lush green leaves. This change in foliage color, known as chlorosis, signals distress and the plant’s attempt to conserve resources. Accurately diagnosing the reason for chlorosis is the first step toward restoring the plant’s health.
Diagnosing Watering Issues
Improper hydration is the most frequent cause of yellowing leaves in Spathiphyllum, presenting with two distinct sets of symptoms. Overwatering deprives the roots of oxygen, causing them to rot and become unable to absorb water or nutrients. When this occurs, the leaves often turn a soft, generalized yellow, sometimes accompanied by a mushy texture or brown spots.
To check for overwatering, ensure the pot has proper drainage holes and verify the soil is not perpetually saturated several days after watering. If the soil remains wet, the plant is at risk of root rot, which causes the plant to wilt even though the soil is saturated. To fix this, allow the top two to three inches of soil to completely dry out before watering again.
In contrast, underwatering results in a dramatic wilting of the entire plant, the peace lily’s signature signal of thirst. If the plant remains dry for too long, the leaves will develop dry, brown, and crispy edges or tips. This yellowing is often preceded by the soil pulling away from the pot’s sides and feeling bone-dry.
The immediate remedy for an underwatered plant is a thorough soaking until water runs freely from the drainage holes. Water deeply only when the top layer of soil has dried out, ensuring the plant receives sufficient moisture without sitting in standing water.
Stress from Light and Temperature
Beyond hydration, the peace lily’s environment plays a significant role in maintaining green foliage. Spathiphyllum naturally grows beneath the canopy of tropical forests, thriving best in bright, indirect light indoors. Placing the plant in a location that receives direct, intense sunlight can quickly lead to leaf stress.
Symptoms of too much light include leaves that appear scorched, bleached, or faded, often developing yellow or brown patches on the side facing the sun. Conversely, insufficient light causes the plant to conserve energy by sacrificing its oldest, lowest leaves, causing them to turn yellow. Moving the plant away from a harsh window or closer to a bright, filtered light source can resolve these issues.
The peace lily prefers a stable temperature range, ideally between 65 and 80°F (18–27°C). As a tropical plant, it is highly sensitive to cold air. Placing the plant near a window, air conditioning vent, or exterior door can expose it to sudden temperature drops or cold drafts. This shock can lead to rapid yellowing and subsequent leaf drop, indicating intolerance for temperatures below 55°F.
Identifying Nutritional Deficiencies and Excesses
The chemical balance within the soil provides another common explanation for yellowing leaves. Peace lilies are sensitive to the buildup of mineral salts from the frequent application of fertilizer. Over-fertilizing can lead to “fertilizer burn,” where excess salts damage the roots and inhibit water absorption.
This excess often presents as browning leaf tips alongside yellowing foliage. The necessary action is to “flush” the soil, which involves running a large volume of water through the pot to dissolve and wash away the accumulated salts.
If the plant has not been fertilized in a long time, the yellowing may be due to a nutrient deficiency, most commonly nitrogen or magnesium. Nitrogen is a mobile nutrient; the plant relocates it from older leaves to support new growth, causing the lower leaves to yellow first. The simplest solution is to apply a balanced, water-soluble houseplant fertilizer, diluted to half the recommended strength, during the active growing season.
Finally, a quick inspection for pests is prudent, as their feeding damage can sometimes mimic nutrient problems. Spider mites, for example, pierce leaf cells to feed, resulting in tiny yellow stippling that can look like generalized chlorosis. Addressing the specific cause—whether watering, light, temperature, or nutrition—is the most effective path to restoring the peace lily’s signature deep green color.