Why Are My Mint Leaves Curling?

Mint rust (Puccinia menthae)

The most serious disease of mint in UK gardens. First symptoms in spring: distorted, swollen, pale yellow, twisted shoot tips and young leaves. As the season progresses: bright orange-yellow to rust-orange powdery pustules on leaf undersides and stems; yellow, orange, or brown discolouration on upper leaf surfaces; leaves curl and distort; plant looks generally sick. Pustules may turn black in late summer (teliospore stage). Overwinters in soil and infected rhizomes; re-infects every year once established.

What to do

• The most effective long-term management is to start fresh: remove all above-ground growth and dispose of it (do not compost); dig out and remove rhizomes from the soil; plant fresh, healthy, rust-free divisions or new plants in fresh compost in a new container or a different area of the garden; choose a relatively disease-tolerant cultivar such as Mentha x villosa 'Alopecuroides' (Bowles's mint); no UK-registered fungicide is approved for mint rust on edible crops for amateur garden use; the rust will re-infect annually once established, so replacing infected plants is the most practical solution.

Drought in containers

The most common cause of day-to-day mint leaf curl in UK gardens. Mint has a high water demand for its rapid growth but is usually grown in containers with limited soil volume. A mint container can go from adequately moist to completely dry within 24 to 48 hours in hot UK summer weather. Drought-stressed mint leaves curl inward rapidly, the plant wilts, and leaves become limp and pale; recovery is very rapid with watering if not prolonged.

What to do

• Check containers daily in hot summer weather; water when the top few centimetres of compost are dry; in a hot UK summer, mint containers may need watering twice daily; use a moisture-retentive multipurpose compost (not a gritty free-draining mix); use a container of at least 30 to 40 cm diameter to give sufficient soil volume; in very hot weather, moving containers to a slightly shadier position in the afternoon reduces water demand and drying rate.

Aphid infestations

Blackfly and other aphid species attack the young, tender shoot tips of mint in spring and early summer, causing the young leaves at the shoot tips to curl, pucker, and distort and the tips to become stunted. The dark-coloured aphid colonies are typically visible on the shoot tips and on the undersides of the curled young leaves in severe infestations.

What to do

• Squash or rub off aphid colonies with fingers, or knock off with a jet of water; for culinary mint, hand control is strongly preferred over insecticides to avoid contaminating the leaves with spray residues; the natural mint aroma may deter some aphids; encouraging ladybirds, lacewings, and parasitic wasps provides ongoing natural control; check shoot tips regularly from April to June.

Mint beetle (Chrysolina menthastri)

A striking, shiny, metallic emerald-green beetle approximately 8 to 10 mm long; both adults and larvae feed on mint leaves causing irregular holes, notches, and scalloped margins that reduce the quantity of healthy edible leaves. Increasingly widespread in UK gardens from spring through summer.

What to do

• Check mint plants regularly from May to August; the metallic green adults are highly visible on the mint leaves; pick off or shake onto a piece of paper or tray; collect and dispose of in soapy water; remove larvae from the undersides of leaves by hand; repeat regularly through the growing season; hand picking is strongly preferred for culinary mint over insecticide sprays; if spray is used, check the product label for edible crop withholding periods and allow 24 to 48 hours before harvesting.

Frequently asked questions

Why are my mint leaves curling?

Mint leaves curl and distort most commonly because of mint rust (Puccinia menthae; most serious disease of UK mint; spring symptoms are distorted swollen pale yellow twisted shoot tips and young leaves; bright orange-yellow to rust-orange powdery pustules develop on leaf undersides and stems; yellow orange or brown discolouration on upper leaf surfaces; start fresh with clean rust-free plants or divisions in fresh compost in a new container; no UK-registered fungicide approved for amateur use on edible mint), drought in containers (most common cause of day-to-day mint leaf curl; check daily in hot weather; water when top few centimetres of compost are dry; may need watering twice daily in hot UK summer; moisture-retentive multipurpose compost; container of at least 30 to 40 cm diameter), aphid infestations on shoot tips (dark-coloured aphid colonies visible on curled distorted shoot tip leaves; squash or rub off with fingers or knock off with water jet; hand control preferred for culinary mint), or mint beetle (Chrysolina menthastri; striking metallic emerald-green adult 8 to 10 mm; irregular holes and notches in leaves; check from May to August; pick off and dispose of in soapy water; hand picking strongly preferred for culinary mint).

What is mint rust and how do I treat it?

Puccinia menthae: a rust fungus specific to Mentha; complex life cycle with multiple spore types. Spring symptoms: distorted swollen pale yellow twisted galled-looking young shoot tips and new leaves. Summer: bright orange-yellow to rust-orange powdery pustules (urediniospores) on leaf undersides and stems; corresponding yellow orange or brown discolouration on upper leaf surfaces; leaves curl pucker and distort; plant looks sick and unproductive. Late summer: pustules may turn black (teliospore stage). Disease cycle: rust-specific to mint; cannot spread to other plant genera; spreads between mint plants via airborne spores; overwinters in soil and in infected rhizomes; re-infects every year once established. Management: most effective long-term management is to start fresh; remove all above-ground growth and dispose of (do not compost); dig out and remove rhizomes; plant fresh healthy rust-free divisions or new plants in fresh compost in a new container or different garden area; Mentha x villosa 'Alopecuroides' (Bowles's mint) is often cited as more rust-resistant; no UK-registered fungicide approved for mint rust on edible crops for amateur garden use.

How do I grow mint in a container in the UK?

Container choice: at least 30 to 40 cm diameter and similar depth; too small a container becomes root-bound within one season; terracotta dries more rapidly than glazed ceramic or plastic (which retain moisture longer, better suiting mint's higher water demand). Compost: good-quality moisture-retentive peat-free multipurpose; NOT a gritty free-draining Mediterranean herb compost; mint requires more moisture than lavender thyme or rosemary. Watering: check daily in hot summer; keep consistently moist but not waterlogged; may need watering twice daily in hot UK summer; the most common cause of sudden mint leaf curl is the container drying out; reduce watering in autumn; rhizomes overwinter in compost and plant dies back above ground before re-emerging in spring. Refreshing: repot every 1 to 2 years in spring; tip out plant select most vigorous healthy rhizome sections discard the rest replant in fresh compost. Position: full sun to partial shade; morning sun and afternoon partial shade can be a good compromise for balancing flavour intensity against reduced watering need.

What is mint beetle and how do I control it?

Chrysolina menthastri (mint beetle): increasingly widespread in UK gardens; related to the rosemary beetle (Chrysolina americana); bright shiny metallic grass-green to emerald-green adult beetle approximately 8 to 10 mm long; larvae grey-green to grey with dark spots and slightly humped back. Life cycle: adults present from spring through summer; eggs laid on mint leaves; larvae hatch and feed alongside adults; pupation in soil; can produce multiple generations per year in warm UK conditions. Feeding damage: both adults and larvae chew from leaf margins inward; irregular holes notches and scalloped margins on leaves; significant defoliation in heavy infestations; significantly reduces quantity of healthy edible leaves. Control: hand picking most effective and most commonly used; metallic green adults highly visible on leaves; pick off or shake onto paper or tray; collect and dispose of in soapy water; remove larvae from leaf undersides by hand; repeat regularly May to August; hand picking strongly preferred for culinary mint over insecticide sprays; if spray used check edible crop withholding period on the product label.