Why Are My Lemongrass Leaves Curling?

Drought and root-bound pots

Lemongrass is thirsty and responds almost immediately to dry compost by rolling its leaves. The rolling is a physiological response that reduces the leaf surface area exposed to the air, slowing water loss until the roots can supply more moisture. In a healthy plant with adequate compost, this rolling reverses within an hour or two of thorough watering. However, a plant in a pot that has become root-bound (where the roots have filled the entire volume of the pot and coiled around the base) cannot absorb water quickly enough even when the compost is adequately moist, because there is too little compost left to hold water around the roots. Root-bound lemongrass shows persistent leaf rolling that does not fully resolve even after watering, alongside very rapid drying of the pot after watering.

What to do

• Water lemongrass whenever the top centimetre of compost is dry. In summer outdoors, this may be daily in hot weather. Water thoroughly until water flows from the drainage holes; do not water little and often.
• Check if the plant is root-bound: if roots are emerging from the drainage holes or circling densely around the inside of the pot, repot into a container one or two sizes larger in spring using fresh, free-draining compost.
• Large, established clumps can be divided in spring: use a sharp spade to split the root mass and repot each division into fresh compost. Division reinvigorates the plant and prevents it from becoming root-bound.

Low humidity

In UK homes in winter, central heating dries the air significantly, often to relative humidity levels of 30 to 40%, well below the 50 to 70% that lemongrass prefers. Low humidity causes the leaf tips to dry and turn brown, and the leaves to roll even when the compost is moist. The rolling caused by low humidity is less dramatic than drought rolling but is persistent regardless of watering frequency.

What to do

• Stand the pot on a gravel tray with water to raise local humidity. Mist the leaves with lukewarm water in the morning. Keep the plant away from radiators and heating vents. Group with other moisture-loving plants.

Cold and draughts

Lemongrass is damaged by temperatures below 10°C and is killed by frost. Cold draughts in winter, from a gap under a door or a draughty window, cause rapid browning of the leaf tips and rolling. The plant goes into a semi-dormant state below 15°C and grows very slowly; below 10°C growth stops and the leaves begin to yellow from the tips downward.

What to do

• Move lemongrass indoors before the first frosts (usually late September to October in the UK). Keep in a minimum temperature of 10°C over winter, ideally 15°C or above. Move away from cold windows and draughts. Reduce watering significantly in winter but do not allow the compost to dry out completely.

Spider mite

Two-spotted spider mite can colonise lemongrass indoors or in a dry greenhouse, causing pale stippling on the leaves and fine webbing between the stems. Lemongrass leaves are tough and the stippling damage is less obvious than on broader-leaved plants, but the leaves may curl and yellow as a severe infestation progresses. Higher humidity deters spider mite and is the best preventive measure.

What to do

• Inspect the inner stems and the base of leaves for mite webbing. Apply insecticidal soap if mites are confirmed. Raise humidity. Introduce Phytoseiulus persimilis predatory mite in a greenhouse for sustained control.

Frequently asked questions

Why are my lemongrass leaves curling?

Lemongrass (Cymbopogon citratus) leaves curl most commonly because of drought, low humidity, or being root-bound in a pot that is too small. Lemongrass is a tropical grass that evolved in humid, warm conditions: its long, flat leaves roll inward along their length when the plant is under water stress, creating a narrower profile that reduces moisture loss. This rolling is the plant's primary response to drought and is almost always reversible once the plant is watered thoroughly. Low humidity in UK homes, particularly in winter, causes the leaf tips and margins to brown and the leaves to roll even when the compost is moist. A pot-bound plant with densely packed roots cannot absorb water quickly enough, even when watered regularly, and shows the same rolling and tip browning as a drought-stressed plant.

How do I grow lemongrass in the UK?

Lemongrass (Cymbopogon citratus) is a tender tropical grass that is not frost-hardy and must be brought indoors in the UK from autumn to late spring. It can be grown outdoors in a pot on a sunny patio from June to September, where it thrives in full sun and warm temperatures. For best results, grow in a large pot (at least 30 centimetres) of well-drained compost. Water generously during the growing season, keeping the compost consistently moist: lemongrass is a thirsty plant that wilts and rolls its leaves quickly if the pot dries out. Feed with a balanced liquid fertiliser every two weeks from May to September. From October, bring the plant indoors to a frost-free, bright position: a heated greenhouse or sunny conservatory is ideal. Reduce watering significantly in winter as the plant slows its growth. Divide congested clumps every two to three years in spring, splitting the root mass with a sharp spade and repotting into fresh compost. Individual stalks can be snipped from the base for culinary use at any time during the growing season.

Why are the tips of my lemongrass leaves turning brown?

Brown tips on lemongrass leaves are caused by low humidity, drought, fluoride or chlorine sensitivity, or cold draughts. Low humidity is the most common cause in UK homes and is especially severe in winter with central heating running: the tips of the long lemongrass leaves dry out and turn brown when the air is too dry. Drought, even brief periods of drying out, damages the leaf tips: lemongrass wilts very rapidly in a dry pot and the tips are the first part of the leaf to show permanent browning after the plant has recovered from wilting. Fluoride or chlorine in tap water can cause tip browning in sensitive plants: using rainwater or allowing tap water to stand overnight before watering reduces this. Cold draughts (near a cold window or door in winter) cause rapid tip browning and leaf rolling. Trim brown tips with sharp scissors at an angle to match the natural leaf shape. Address the underlying cause to prevent new browning.

Can I grow lemongrass from a supermarket stalk?

Yes, lemongrass stalks bought from a supermarket can often be propagated into growing plants if the root base is intact and fresh. Choose stalks with a firm, pale base at least 5 centimetres long and with some of the pale lower section showing. Place the stalks in a glass or jar of water, changing the water every few days, and position in a warm, bright spot. Roots and new growth typically appear within 2 to 4 weeks if the stalks are fresh and viable. Once a good root system has developed (roots 3 to 5 centimetres long), pot up into compost and grow on. Not all supermarket stalks will root: stalks that have been stored cold for a long time, or that have been trimmed too short, may not have viable root material. Fresh stalks with a plump, intact base are most likely to succeed.