Lemongrass is a fragrant herb popular for its culinary and aromatic qualities, adding a tropical touch to gardens. However, brown leaves are a common concern, raising questions about plant health. Understanding the factors contributing to this browning helps maintain a thriving lemongrass plant.
Common Reasons Lemongrass Turns Brown
Brown leaves on lemongrass can indicate several underlying issues, ranging from environmental stress to natural processes. Identifying the specific symptoms helps in diagnosing the problem.
Watering Issues
Both insufficient and excessive watering can lead to brown lemongrass leaves. Underwatering causes leaves to dry out and become crispy, especially at the tips, as the plant struggles to draw moisture. Conversely, overwatering results in soggy, soft brown leaves, often with yellowing, due to waterlogged soil leading to root rot. Lemongrass thrives in consistently moist, but not saturated, soil.
Light and Temperature Stress
Lemongrass prefers full sun, needing 6 to 8 hours of direct sunlight daily. Too much intense sunlight, especially in hot climates, can scorch leaves, causing brown spots. Conversely, consistently low temperatures or frost exposure can cause significant browning, as lemongrass is a tropical plant sensitive to cold. Temperatures below 40°F (4°C) can severely damage or kill the plant.
Nutrient Deficiencies
A lack of essential nutrients can contribute to leaf browning. Lemongrass is a heavy feeder, particularly requiring nitrogen for healthy green growth. In nutrient-poor soil or depleted containers, the plant may exhibit browning, starting with older leaves. Deficiencies in potassium or magnesium can also lead to browning leaf edges.
Pests and Diseases
Although often considered pest-resistant due to its citral content, lemongrass can be affected by certain pests and diseases. Sap-sucking insects like spider mites or aphids feed on leaves, causing discoloration, speckling, and browning as they extract plant fluids. Fungal diseases such as rust (Puccinia nakanishikii) and leaf blight also cause browning. Rust appears as light yellow spots with brown streaks and pustules, while leaf blight results in reddish-brown spots on leaf tips and margins.
Natural Plant Cycle
Browning leaves are sometimes a natural part of the lemongrass plant’s life cycle. As older leaves age, they naturally degrade, turning brown and drying out as the plant reallocates nutrients to new growth. This process is normal, making way for fresh shoots. In colder climates, lemongrass may also naturally die back and turn brown during winter dormancy.
Solutions and Prevention for Brown Lemongrass
Addressing the causes of browning involves specific adjustments to care practices, promoting healthier growth and preventing future issues.
Adjusting Watering Practices
Consistent moisture is important for lemongrass. To prevent browning from underwatering, water deeply when the top inch or two of soil feels dry. Potted plants may need daily watering in hot, dry weather due to increased evaporation. To avoid overwatering, ensure the soil is well-draining, whether in the ground or in containers. Containers should have adequate drainage holes to prevent waterlogging and root rot.
Optimizing Environmental Conditions
Lemongrass thrives in warm, sunny environments. If intense sun causes scorching, provide partial shade during the hottest part of the day. In regions with cooler temperatures, grow lemongrass in containers for easy relocation indoors when temperatures drop below 40°F (4°C), protecting the plant from cold damage. Maintaining moderate to high humidity, ideally 40% to 60%, is also beneficial.
Providing Essential Nutrients
Regular fertilization supports vigorous growth and helps prevent nutrient deficiencies. Apply a nitrogen-rich fertilizer during the active growing season, typically spring and summer. A balanced fertilizer with an NPK ratio like 6-4-0 or similar can be used weekly or monthly. Incorporating organic matter such as compost or well-rotted manure improves soil structure and nutrient content.
Identifying and Treating Pests or Diseases
Regularly inspect lemongrass plants for early signs of pests, such as tiny insects or webbing. Aphids and spider mites can be dislodged with a strong spray of water or treated with insecticidal soap or neem oil. For fungal diseases like rust or leaf blight, remove infected leaves promptly with clean shears. Avoiding overhead watering helps reduce the spread of fungal spores, as they thrive in humid conditions.
Regular Pruning and Maintenance
Pruning brown or damaged leaves helps maintain plant health and encourages new growth. Remove any dead or discolored outer stalks and leaves. In colder climates where lemongrass goes dormant and turns brown, a drastic cut back to a few inches above the tender white part of the stalk in early spring promotes robust new growth. Regularly raking away fallen debris from around the plant also helps prevent disease.
Harvesting Lemongrass and Natural Browning
Browning can also indicate that lemongrass stalks are maturing and ready for harvest. As the plant develops, the outer leaves of mature stalks naturally turn brown and dry. This browning indicates the stalk has reached its full development and flavor. Identify mature stalks by looking for those at least 12 inches tall and about half an inch thick at the base. When harvesting, pull or cut the entire stalk at the base; outer brown leaves are typically removed before use.