Lemongrass is a popular herb valued for its distinct citrusy aroma and versatility in culinary and aromatic applications. This tropical plant, known for its tall, graceful stalks, brings a vibrant green presence to gardens. A thriving lemongrass plant typically displays a lush, verdant appearance.
What Healthy Lemongrass Looks Like
A healthy lemongrass plant exhibits robust growth with upright, firm, vibrant green stalks. Its long, slender leaves arch gracefully, forming a dense, grassy clump. This lush foliage indicates sufficient moisture and nutrient uptake, reflecting the plant’s overall vigor. The stalks should feel firm and emit a strong, fresh, lemony scent when bruised.
Why Lemongrass Turns Yellow
Lemongrass leaves can turn yellow due to various factors, often signaling underlying issues with the plant’s health or environment. Understanding the specific cause is the first step toward restoring its green vitality.
Nutrient Deficiencies
Lack of essential soil nutrients is a common reason for yellowing in lemongrass. As a heavy feeder, it requires a consistent supply of nutrients for lush growth. Nitrogen deficiency often results in general pale green or overall yellowing of older leaves, as nitrogen is crucial for chlorophyll production. Iron deficiency can also cause yellowing, typically appearing as yellowing between the veins of younger leaves while the veins remain green.
Watering Issues
Improper watering, whether overwatering or underwatering, can lead to yellowing leaves. Overwatering saturates the soil, depriving roots of oxygen and leading to root rot, which hinders nutrient absorption, resulting in yellow or brown foliage. Conversely, underwatering causes dehydration and stress, manifesting initially as wilting and stunted growth before leaves yellow.
Pest Infestations
Pests can sap the plant’s vitality, causing leaves to yellow and decline. Common culprits include aphids, small sap-sucking insects that cause yellowing and curling. Mealybugs also feed on plant sap, leading to wilting and yellowing, often leaving a waxy residue. Spider mites, tiny arachnids thriving in dry conditions, cause stippling and yellowing, sometimes with visible webbing.
Environmental Stress
Lemongrass is sensitive to extreme environmental conditions, which can cause yellowing. Exposure to cold temperatures, especially below 50°F (10°C) or frost, can severely damage the plant and cause discoloration. Insufficient light results in slow growth and pale or yellowing leaves, while too much direct sunlight, particularly in very hot climates, can scorch the foliage and cause leaf burn or dehydration.
Natural Aging
As lemongrass plants mature, older, lower leaves naturally yellow and die back. This process is part of the plant’s normal growth cycle as it prioritizes energy for new foliage production. This type of yellowing is typically uniform on the oldest leaves and differs from problematic yellowing, which often affects newer growth or appears irregularly across the plant.
Addressing Yellowing Lemongrass
Addressing yellowing in lemongrass involves targeted actions based on the identified cause. Prompt intervention can help restore the plant’s health and vibrant green color.
For nutrient deficiencies, apply a balanced liquid fertilizer or one rich in nitrogen, which promotes green foliage. A 10-6-4 NPK ratio is often recommended. If overwatering is the issue, allow the soil to dry out significantly before the next watering and ensure the pot has adequate drainage holes to prevent waterlogging. Conversely, if underwatering is suspected, provide a thorough, deep watering, ensuring the soil is consistently moist but not soggy.
For pest infestations, insecticidal soap or neem oil can control aphids, mealybugs, and spider mites. A strong spray of water can also dislodge many pests. For environmental stress, move the plant to a location with appropriate light exposure; shadier if too much sun, brighter if lacking light. If cold temperatures are a concern, bring potted plants indoors or provide frost protection. When yellowing is due to natural aging, simply trim off the discolored leaves at the base to encourage new growth.
Preventing Lemongrass Yellowing
Proactive care practices are essential for maintaining the health of lemongrass and preventing leaves from turning yellow.
Consistent watering is important; keep soil moist but not waterlogged by checking the top inch before watering. Regular feeding with a balanced fertilizer during the growing season replenishes essential nutrients like nitrogen, phosphorus, and potassium, crucial for healthy leaf development. Providing adequate sunlight, ideally 6 to 8 hours of direct sun daily, supports robust growth and prevents pale foliage.
Maintain suitable temperatures; lemongrass prefers warm conditions and needs protection below 50°F (10°C). Routine pest checks help catch infestations early, allowing timely intervention. Ensuring good air circulation, especially in dense clumps, discourages fungal issues and pest habitats. Finally, planting in well-draining soil rich in organic matter prevents root problems and supports overall plant health.
Is Yellowed Lemongrass Usable?
Usability of yellowed lemongrass depends on the cause of discoloration. Leaves yellowed due to natural aging or minor, temporary environmental stress are generally still suitable for culinary or aromatic purposes. These may have a slightly diminished flavor or aroma compared to vibrant green ones, but typically pose no health risk. Use them in applications where flavor intensity is less critical, such as in teas or broths.
However, if yellowing results from severe pest infestations, significant disease, or root rot from overwatering, discard the affected leaves. Pests like mealybugs or fungal diseases like rust can compromise the plant’s integrity and potentially introduce undesirable elements. Leaves showing signs of mold, rot, or widespread decay should always be removed and not used.