The Aloe vera plant is a popular succulent known for its fleshy leaves and resilience to drought. When the deep green color of the leaves fades to yellow, it signals the plant is under significant stress. Diagnosing the exact cause requires careful examination of the plant’s symptoms and environment, as yellowing can be triggered by several distinct issues.
The Overwatering Trap
The most frequent cause of yellowing in Aloe vera is excessive soil moisture, which compromises root health. Aloe roots require oxygen; when the soil remains saturated, water displaces air pockets, creating an anaerobic environment. This lack of oxygen triggers root rot, where the roots decay due to fungal or bacterial pathogens.
When the root system is damaged, it loses its ability to absorb water and nutrients, causing the leaves to turn yellow. Overwatered leaves become soft, mushy, and often translucent, sometimes developing water-soaked spots. The yellowing often starts at the base of the leaf and progresses upward.
To remedy this, the plant must be removed immediately from the wet potting medium to inspect the roots. Healthy roots are firm and white, while rotted roots are brown, black, and soft. Any decayed material should be trimmed away with a sterile tool before repotting the aloe in fresh, fast-draining succulent or cactus mix. The new pot must have functioning drainage holes. A proper watering technique involves a deep soak that completely saturates the soil, followed by allowing the soil to become bone-dry before the next application.
Environmental Stressors
Beyond moisture issues, light intensity and temperature fluctuations are common external factors that lead to yellowing in aloe leaves. Although succulents require bright light, placing an indoor plant directly under intense, unfiltered sun can cause sun stress or sunburn. This damage appears as pale yellowing or a bleached, reddish-yellow tinge that typically starts on the tips and upper surfaces of the leaves.
The solution is to gradually acclimate the plant to its new location by providing bright, indirect light. Conversely, if an aloe is kept in very low light conditions, it may exhibit pale yellowing due to insufficient energy production. While inadequate light more commonly results in elongated, weak growth, a lack of photosynthesis can eventually cause the foliage to lose its vibrant green color.
Temperature extremes also contribute to yellowing, as Aloe vera is a semi-tropical plant. Exposure to cold drafts or temperatures consistently below 50°F (10°C) can cause cellular damage within the fleshy leaves. The plant tissue responds by turning yellow and becoming soft or mushy, a sign of irreversible cold damage. To prevent this, indoor aloes should be situated away from drafty windows, air conditioning vents, and exterior doors during cooler months.
Addressing Pests and Nutrient Imbalances
Less common, but equally damaging, are pest infestations and chronic nutrient deficiencies. Pests such as mealybugs and scale insects are sap-sucking insects that feed on the plant’s internal fluids. They congregate in leaf crevices or on the undersides of the foliage, depleting the plant’s resources and causing a systemic weakening that results in yellowing.
Treating a mild infestation involves using a cotton swab dipped in rubbing alcohol to physically remove the pests, or applying horticultural oils like neem oil. Yellowing can also be symptomatic of a nutrient imbalance, particularly a deficiency in nitrogen, a component necessary for chlorophyll production. This typically manifests as uniform yellowing across the older, lower leaves as the plant mobilizes the limited nitrogen to new growth.
While aloes are adapted to nutrient-poor soils and rarely require feeding, a light application of a balanced, liquid fertilizer formulated for succulents can correct a confirmed deficiency. Over-fertilizing is a significant risk, as it can burn the roots and cause a toxic buildup of salts, which triggers yellowing and leaf damage. Fertilizing once or twice during the active growing season is sufficient to maintain proper nutrient levels.