Lemongrass Turning Brown? Fix Brown Tips, Rust, and Frost Damage Fast

The first instinct when lemongrass turns brown is to water more. Sometimes that’s right — but eight distinct problems produce similar-looking damage on lemongrass, and treating Puccinia rust the same way you’d treat drought stress can make things significantly worse. Frost damage looks nothing like root rot once you know what to check, and nitrogen deficiency browns the plant from the bottom up while iron deficiency starts at the top. Getting the diagnosis right takes about 30 seconds with the right framework.

This guide covers the eight most common lemongrass problems — including how to distinguish them visually, the biological mechanism behind each one, and the fix that matches. There’s also a section on when not to treat, because over-treating healthy stress is one of the most common mistakes.

Quick Diagnostic Table: Lemongrass Problems at a Glance

Match the visual symptom in the first column to identify your problem before reading the full sections below.

For detailed guidance on each problem — including when to skip treatment entirely — continue below.

Brown Tips and Leaf Scorch

Tip browning is the most common complaint about lemongrass, and most of it is harmless. Outer leaves on a healthy clump brown and dry naturally as the plant ages — the same mechanism you see in ornamental grasses. Those crispy tips peel away easily and signal nothing wrong.

When browning is a problem, it’s usually underwatering. Lemongrass has long, high-surface-area blades that transpire heavily in hot weather. When root uptake can’t keep pace with that water loss, the leaf tip — the point farthest from the root system and last to receive water — dies first. In practice this means the top inch or two of multiple blades go tan and crispy simultaneously while the base of the plant looks fine.

Fix it by watering deeply rather than shallowly. Let water penetrate 6–8 inches to reach the root mass instead of just wetting the surface. A 2–3 inch mulch layer cut soil moisture loss dramatically, especially in USDA zones 8–10 where summer heat is intense. According to UF/IFAS Extension, lemongrass needs consistent moisture and performs best when soil never fully dries out during the growing season [2].

Persistent tip browning on a well-watered plant in full shade points to a different cause: insufficient light. Lemongrass needs at least 6 hours of direct sun daily. Without it, chlorophyll breaks down faster than it’s produced and blades go yellow-brown from the tips inward. Moving the pot or cutting back surrounding plants to improve light exposure fixes this within 2–3 weeks.

Frost Damage

Lemongrass (Cymbopogon citratus) is native to tropical Southeast Asia and has virtually no cold tolerance. Foliage begins to suffer when temperatures fall below 40°F (4°C), and a hard frost collapses the entire plant within hours [4].

The visual signature of frost damage is distinct from drought: instead of crispy brown tips, frost-hit foliage goes limp and straw-colored all at once. The blades lose their structure completely — they droop rather than standing upright — and by the next morning the entire aerial part of the plant may look dead.

The critical question is whether the roots survived. Squeeze the white bulb-like base of the plant at soil level. If it feels firm and white inside, the growing point is intact and the plant will regrow. If it’s mushy, dark, or has turned to liquid, the crown is gone and the plant is dead [5].

For plants with viable crowns after frost:

• Cut all foliage back to 2–3 inches above the white section — leave nothing brown standing
• Apply 4–6 inches of straw mulch over the crown immediately to buffer the soil from further freezing
• Do not fertilize or disturb the plant until you see new green shoots emerging
• In zones 9–10, expect regrowth within 6–8 weeks once nighttime temperatures stabilize above 45°F; in zone 8b, regrowth may take longer depending on winter severity [4]

In zone 7 and below, the roots will not survive outdoor winters without protection. Dig and pot plants before first frost, bring them into a cool indoor space (50–60°F), water only once per month, and replant after your last frost date the following spring.

Lemongrass Rust

Rust is the most serious disease affecting lemongrass in the US and the one most often misidentified as simple browning. The pathogen, Puccinia nakanishikii, is a biotrophic fungus — it infects only living plant tissue — and once established it can defoliate a plant rapidly in warm, humid conditions.

The disease first appeared in Hawaii, then spread to California, New Zealand, and Thailand. It reached Florida in February 2013 when it was confirmed in Miami-Dade County, according to a study published in Plant Disease [3]. Warm, wet summers across the Southeast and coastal California make those regions the highest-risk areas for US gardeners.

How to identify it: Flip a suspicious leaf over and look at the underside. Rust produces characteristic dark cinnamon-brown pustules (uredia) on the undersides of leaves. The upper surface shows corresponding yellow-orange streaks or elongated spots running parallel to the leaf veins [1]. As the infection progresses, small spots merge into large necrotic patches that can cover most of the leaf blade [3]. If you only look at the top side, early rust looks like irregular yellowing — the pustules beneath are what confirm the diagnosis.

Spores spread by wind, rain, and water splash, which is why overhead irrigation turns minor infections into major ones fast [1]. Management focuses on removing infected leaves immediately (bag them — don’t compost, as spores survive in debris), avoiding all overhead watering, and spacing plants adequately so foliage dries quickly after rain.

For fungicide treatment, neem oil (marketed as Trilogy) is the only product currently labeled specifically for lemongrass rust. Apply every 7–14 days during active disease pressure. Using neem oil correctly matters — coverage of leaf undersides is essential since that’s where spores germinate. Healthy, vigorously fertilized plants also outgrow mild infections faster than stressed ones, so maintaining a regular feeding schedule (half-strength balanced fertilizer weekly in summer [2]) is part of the management approach, not just disease prevention. Read more about preventing and treating fungal infections for a broader framework.

Leaf Blight

Leaf blight — caused by Colletotrichum spp. and Curvularia spp. — produces reddish-brown spots concentrated on leaf tips and margins, with defined edges rather than the diffuse streaks of rust [2]. The spots look scorched rather than pustular. Flip the leaf over and you’ll find no orange powder — that’s the key difference.

Blight thrives in the same wet, humid conditions as rust but spreads primarily by rain splash rather than airborne spores. Dense, crowded clumps trap moisture and create the micro-environment the pathogen needs. Prune infected growth, remove it from the site, and divide clumps that have grown too thick to allow airflow. Copper-based fungicide applied at the first sign of infection prevents spread. Switching from overhead to drip or hand-watering removes the main infection vector [2].

Overwatering and Root Rot

Root rot is the problem most likely to kill lemongrass completely, and it develops faster in containers than in garden beds. The mechanism: waterlogged soil depletes oxygen around the roots, forcing them into anaerobic respiration. Ethanol and other toxic byproducts accumulate, cell membranes break down, and roots die. With the root system gone, water and nutrient uptake collapses — leaves yellow, soften, and eventually brown from the bottom up.

The visual pattern is different from underwatering: overwatered leaves feel limp and soft rather than crispy, and the damage spreads uniformly from the base rather than starting at tips. Pressing the base of the plant may reveal a spongy, darkened stem. A sour or sulfurous smell from the soil is a late-stage indicator of anaerobic decomposition [2].

To confirm, unpot the plant and examine the roots. Healthy lemongrass roots are firm and white. Roots killed by rot are brown to black, soft, and fibrous — they pull apart when gently tugged. Trim all rotted material with clean scissors, dust cut ends with powdered cinnamon (a mild antifungal) or apply a copper fungicide drench, and repot in fresh mix with 20–30% perlite added for drainage. Water only when the top inch of soil feels dry going forward.

Nutrient Deficiency and Yellowing

Two distinct yellowing patterns point to two different deficiencies, and treating one with the solution for the other is wasted effort.

Nitrogen deficiency: Older, lower leaves yellow first while upper growth stays green. Nitrogen is a mobile nutrient — when supply is short, the plant actively pulls it from older tissue and redirects it to new growth, according to UConn Extension [6]. This bottom-up yellowing pattern in a healthy-looking plant is almost always nitrogen. Container-grown lemongrass is particularly susceptible because regular watering flushes available nitrogen out of the potting mix. Fix it with a nitrogen-forward balanced fertilizer at half-strength weekly during the growing season [2].

Iron deficiency (interveinal chlorosis): New upper leaves yellow between the veins while the veins themselves stay green, and the older lower leaves remain normal. Iron is immobile in plants — deficiency symptoms appear on the newest growth first because existing iron can’t move to where it’s needed [6]. The most common cause isn’t absent iron in the soil but high pH making it unavailable: iron becomes chemically locked in soil compounds above pH 7.0. Test your soil pH before adding fertilizer. If pH is above 7.0, sulfur amendment or chelated iron (which bypasses pH chemistry) resolves it faster than standard fertilizers.

Spider Mites and Aphids

Pest infestations on lemongrass are the exception rather than the rule — UF/IFAS extension notes that lemongrass is generally free of pests when grown correctly [2]. When they appear, it’s almost always on stressed plants: those that are underwatered, over-crowded, or weakened by disease.

Spider mites leave a distinctive white or yellow stippling across the blade surface — individual feeding punctures that become visible under a hand lens. Fine webbing on leaf undersides confirms the diagnosis. In hot dry weather, populations can explode in days. Start with a strong jet of water aimed at leaf undersides to physically dislodge colonies. Follow with insecticidal soap if the infestation persists after 48 hours [2].

Aphids cluster at new shoot tips and leave sticky honeydew residue. The same water-spray-first approach works; neem oil handles persistent colonies. Avoid broad-spectrum insecticides that also kill the predatory insects (lacewings, ladybugs, parasitic wasps) that would otherwise do the job for free.

When NOT to Treat

Over-treating is as common a mistake as under-treating, and some lemongrass “problems” require no intervention at all.

• A few brown tips on outer blades: Natural aging. Trim if it bothers you aesthetically; the plant is fine.
• Yellowing leaves after repotting: Transplant shock, not deficiency. Wait two weeks before adding fertilizer — the roots need to establish before they can use additional nutrients.
• Mild rust on a plant you’re about to harvest for cooking: Harvest the whole plant and cut it back hard. Fresh regrowth will be clean and is faster than waiting for fungicide to work.
• Winter die-back in zones 8b–9: Brown straw-colored foliage in winter is dormancy, not death. Check the base before discarding — the crown is usually alive. Wait until spring to assess.
• Single-stem aphid infestation: If one shoot is affected and the rest of the plant is healthy, remove that shoot and monitor. Beneficial insects typically resolve small colonies without spraying.

Prevention: Making Lemongrass Trouble-Free

Most lemongrass problems trace back to a small number of cultural mistakes. Fix these and the diagnostic table above stays mostly unused.

Water at soil level, never overhead. This single change eliminates the primary infection vector for both rust and leaf blight. Hand-watering or drip irrigation keeps foliage dry and dramatically reduces fungal pressure [2].

Give it full sun. Six or more hours of direct sunlight daily keeps plants growing vigorously. Vigorous plants outgrow mild rust infections, recover from pest pressure faster, and produce the essential oils that may provide some natural pest resistance.

Don’t crowd the clump. Lemongrass expands to 3–4 feet wide and develops dense interior foliage that stays wet after rain. Divide clumps every 2–3 years and space divisions at least 3 feet apart to maintain airflow. A crowded clump creates the microclimate both blight and rust need to establish.

Feed consistently, not reactively. Apply half-strength balanced fertilizer weekly from June through September for container plants, or monthly for in-ground plants with amended soil [2]. Consistent nutrition keeps the plant in the vigorous growth window where it shrugs off minor fungal and pest pressure before it becomes a problem. Start with a strong foundation — you can read the complete lemongrass growing guide for full cultural recommendations.

Frequently Asked Questions

Why is my potted lemongrass turning brown in summer?
Container plants dry out faster than in-ground ones, especially in terracotta pots. Check soil moisture daily in summer — if the top inch is dry, water thoroughly. Consistent underwatering is the leading cause of browning in container lemongrass.

Can lemongrass recover from a hard frost?
Yes, if the growing crown at the base survived. Squeeze the white base section at soil level — firm and pale means alive. Cut all brown foliage back to 2–3 inches above the white portion, mulch heavily, and wait. In zones 8b–9, regrowth typically appears within 6–8 weeks of consistent warm nights [5].

How do I tell lemongrass rust from brown tips?
Flip the leaf over. Rust produces visible dark cinnamon-brown pustules on the underside; tip browning from drought or aging does not. Rust also causes yellow-orange streaks running parallel to the veins on the upper surface, while drought causes uniform tanning from the tip downward [1].

Is it safe to use lemongrass for cooking if it has rust?
Remove and discard infected leaves. The stalks — the lower white portion used in cooking — are below the infection site and remain safe to use. Harvest, remove all infected foliage, and the plant will regenerate clean growth within a few weeks.

Sources

1. Penn State University, PlantVillage. “Lemon Grass Diseases and Pests.”
2. UF/IFAS Extension, Nassau County. “Fact Sheet: Lemongrass.”
3. Schubert, T.S. et al. “First Report of Rust Caused by Puccinia nakanishikii on Lemongrass in Florida.” Plant Disease, 2014.
4. Gardeners Path. “Lemongrass Winter Care: How to Prepare for the Cold.”
5. Savvy Gardening. “Is Lemongrass a Perennial? Yes and Here’s How to Overwinter It.”
6. UConn Extension. “Watch Out for These Nutrient Deficiency Symptoms.” 2024.