Plant problems

Why Are My Cymbopogon Leaves Curling?

Q: How do I overwinter cymbopogon (lemongrass) in the UK?

Overwintering Cymbopogon citratus (lemongrass) successfully in the UK requires bringing the plant indoors before the first autumn frosts and maintaining it in a warm enough position with adequate light through the winter months. Timing: bring indoors in September or October before the night temperatures drop below 10 to 12°C; even before a frost, temperatures consistently below 10°C slow the plant significantly and below 5°C cause leaf curl and yellowing. Position: a warm, bright conservatory, heated greenhouse, or a very sunny south-facing windowsill are the best overwintering positions; the plant needs the warmest, brightest indoor position available. Temperature: maintain above 10°C at night as a minimum; above 15°C is significantly better for maintaining healthy, active growth through winter; below 10°C the plant is alive but markedly slowed, and the leaf tips curl and yellow progressively through winter. Light: a south-facing windowsill or a position close to a south-facing window provides the best available winter light in a UK home; supplementary LED grow lighting can extend the effective day length and light intensity for overwintered lemongrass in a dark UK winter. Watering: reduce watering significantly compared with the summer growing season; in cool winter conditions the plant is largely dormant and excess watering leads to root problems; water only when the top 3 to 4 cm of compost is dry; never allow the pot to stand in water. Feeding: do not feed through winter; resume feeding with a balanced liquid fertiliser from March or April when temperatures rise and active growth resumes. In late spring (May), harden off gradually and move outdoors after the last frost risk has passed.

Q: How do I grow cymbopogon citratus from a supermarket stem?

Cymbopogon citratus (lemongrass) can be propagated in the UK from fresh lemongrass stems purchased in a supermarket or Asian food store, as long as the stems have their pale, swollen base intact (the stalks have not been trimmed too short) and are reasonably fresh. The propagation process is as follows: select stems that have a pale, bulb-like base at least 3 to 5 cm long; old, dried, or very short-cut stems have a lower success rate. Place the stems in a tall, narrow glass or jar with 3 to 5 cm of water covering the base; place in a warm, bright, sunny windowsill position (a south-facing windowsill in spring or early summer gives the best results); change the water every two to three days to prevent bacterial buildup. After one to three weeks in warm conditions (above 20°C), roots begin to emerge from the base of the stem; the roots are pale, thread-like, and emerge from the cut base of the stem; new pale green shoots may also begin to emerge from the leaf bases. Once the roots are 2 to 4 cm long, pot the rooted stem into a pot of compost mixed with perlite or horticultural grit (a free-draining mix is important for root development); plant so the pale stem base is at or just below the compost surface; water well and place in a warm, sunny position. Water regularly and begin liquid feeding after six to eight weeks when the plant has established new root growth and is actively producing new leaf growth. The plant can be moved outdoors into a warm, sheltered, sunny position after the last frost risk has passed (typically late May in most of the UK).

Q: Which cymbopogon species are used in cooking and herbal medicine?

Cymbopogon is a large genus of tropical and subtropical aromatic grasses with a wide range of culinary, medicinal, and aromatic applications across South and Southeast Asia, Africa, and South America: Cymbopogon citratus (West Indian lemongrass, lemon grass): the principal culinary lemongrass; the swollen, pale stem base is used in Thai, Vietnamese, Indonesian, and other South and Southeast Asian cuisines in curries, soups, and pastes; very widely cultivated in tropical and subtropical countries and as a kitchen herb in the UK. Cymbopogon flexuosus (East Indian lemongrass, Cochin lemongrass, Malabar grass): another culinary and essential oil lemongrass from India; the main commercial source of lemongrass essential oil; the oil is used widely in food flavouring, cosmetics, soaps, and aromatherapy; both this and C. citratus produce the characteristic lemony aroma from the compound citral (a mixture of geranial and neral). Cymbopogon nardus (citronella grass): the source of citronella essential oil, widely used as an insect repellent, particularly against mosquitoes; the characteristic smell of citronella candles and insect repellent sprays; grown commercially in tropical Asia and Africa. Cymbopogon martinii (palmarosa grass): the source of palmarosa essential oil, used in perfumery, cosmetics, and aromatherapy; a sweet, rosy-geranium floral scent quite different from the lemony scent of C. citratus or C. nardus. Cymbopogon winterianus (Java citronella): another commercial source of citronella oil, producing higher oil yields than C. nardus; widely grown in tropical Asia for the essential oil industry. The aromatic compounds in cymbopogon species are produced in specialised oil glands distributed throughout the leaf tissue and are released when the leaves are crushed or bruised; the fragrance varies from the strongly lemony scent of lemongrass to the rosy-geranium scent of palmarosa.

Cymbopogon citratus (lemongrass) is a tropical culinary and ornamental grass grown in UK gardens as a tender perennial for its fragrant, lemon-scented, arching leaves and edible stem base. Not frost-hardy; in the UK it must be overwintered indoors above 10°C. Leaves curl and yellow from cold temperatures, insufficient winter light, or drought in a hot summer position.

Cold damage and low temperatures

Cymbopogon is a tropical grass not frost-hardy in the UK; temperatures below 5 to 10°C cause the leaf tips to turn yellow or brown and curl inward, and temperatures below 5°C cause rapid yellowing, curling, and collapse of the above-ground stems. The transition from warm outdoor summer conditions to a cool autumn or indoor environment is a common trigger for significant leaf curl and tip browning in UK-grown plants.

What to do

Bring indoors in September or October before night temperatures drop below 10 to 12°C. Overwinter in the warmest, brightest available indoor position (heated conservatory, greenhouse, or south-facing windowsill) at a minimum of 10°C (15°C is significantly better). Reduce watering through winter; do not feed until active growth resumes in spring. Harden off and move outdoors after last frost risk in late May. Existing curled and browned leaf tips do not recover; remove damaged leaves when the plant resumes active growth in spring.

Insufficient light

A tropical sun-lover, lemongrass requires bright direct light for best growth; in the lower light of a UK greenhouse, conservatory, or windowsill through autumn and winter, new leaves are narrower and paler, and existing leaves yellow at the tips and curl. Insufficient light combined with cool winter temperatures is the most common combined stress for a UK-overwintered lemongrass plant.

What to do

Position in the brightest available indoor location, as close to a south-facing window as possible. Consider supplementary LED grow lighting to extend effective day length and light intensity through the darkest UK winter months (November to February). Even with the best available indoor light in a UK winter, some leaf tip yellowing and curl is normal; the plant fully recovers in spring and summer when moved outdoors or given summer light levels.

Drought in summer

In a container in a hot, sunny UK summer position, particularly in a terracotta pot that dries quickly, lemongrass can dry out rapidly between waterings. The large, broad leaves transpire quickly and the leaf tips brown, curl, and dry if the root zone dries out for extended periods. The plant recovers quickly when watering is resumed but the existing curled and browned leaf tips do not recover; remove them after watering is restored.

What to do

In a hot summer, water container-grown lemongrass deeply every two to three days; in very hot, exposed, sunny conditions, daily watering may be necessary. Use a moisture-retentive compost rather than a gritty free-draining mix in a container; add a layer of mulch on the surface of the compost to slow evaporation. A larger container retains moisture longer than a small pot; pot up into a larger container in spring as the plant grows.

Frequently asked questions

Why are my cymbopogon leaves curling?

Cymbopogon leaves curl most commonly because of cold damage and low temperatures (tropical grass; temperatures below 5 to 10°C cause tip curl and yellowing; bring indoors in September to October; overwinter above 10°C in the warmest, brightest indoor position; reduce watering and stop feeding; harden off and move outdoors after last frost in late May), insufficient light (bright direct light required; lower indoor light in UK autumn and winter causes tip yellowing and curl; south-facing windowsill; consider supplementary LED grow lighting November to February), or drought in summer (containers in hot sunny positions dry quickly; water deeply every two to three days or daily in very hot conditions; moisture-retentive compost; larger containers retain more moisture). Cold damage is the most common UK issue.

How do I overwinter cymbopogon (lemongrass) in the UK?

Bring indoors in September to October before night temperatures drop below 10 to 12°C. Warmest, brightest available indoor position; heated conservatory, greenhouse, or very sunny south-facing windowsill. Maintain above 10°C at night minimum (15°C significantly better for active growth). Reduce watering; water only when the top 3 to 4 cm of compost is dry; never allow the pot to stand in water. Do not feed through winter. Resume feeding with balanced liquid fertiliser from March or April as active growth resumes. Harden off gradually and move outdoors in late May after last frost risk has passed.

How do I grow cymbopogon citratus from a supermarket stem?

Select fresh stems with an intact pale, swollen base at least 3 to 5 cm long. Place in a tall, narrow glass with 3 to 5 cm of water covering the base; warm, bright, sunny windowsill; change water every two to three days. After one to three weeks in warm conditions (above 20°C), pale thread-like roots emerge from the cut base. Once roots are 2 to 4 cm long, pot into free-draining compost mixed with perlite or horticultural grit; plant the pale stem base at or just below the compost surface; water well; sunny, warm position. Begin liquid feeding after six to eight weeks. Move outdoors after last frost (late May in most of the UK).

Which cymbopogon species are used in cooking and herbal medicine?

C. citratus (West Indian lemongrass): the principal culinary lemongrass; swollen pale stem base used in Thai, Vietnamese, and Indonesian cuisine. C. flexuosus (East Indian lemongrass): the main commercial source of lemongrass essential oil (food flavouring, cosmetics, aromatherapy); both species produce citral, the compound responsible for the lemony aroma. C. nardus (citronella grass): source of citronella oil, widely used as an insect repellent; the smell of citronella candles. C. martinii (palmarosa grass): source of palmarosa oil, used in perfumery (sweet, rosy-geranium scent). C. winterianus (Java citronella): higher-yield commercial citronella oil source.