Catmint (Nepeta x faassenii, N. cataria, N. racemosa 'Walker's Low') is one of the hardiest, most drought-tolerant perennials in the UK cottage garden repertoire, beloved for its silver-grey foliage, lavender-blue flower spikes, and value as a pollinator plant. When the leaves start to curl it is nearly always one of two things: aphids in spring, or powdery mildew from midsummer onward. Cats rolling in the plant, flea beetles, waterlogged soil, and botrytis after a wet cut-back are less common but worth knowing about.
Quick diagnosis
- Curled, matted shoot tips with pale green insects in spring: Aphids. Blast off with water or use insecticidal soap.
- White powdery coating on curling, distorted leaves from midsummer: Powdery mildew. Cut back hard.
- Crushed, flattened stems and bruised leaves with no pests: Cat damage. Physical protection for new plants.
- Tiny round holes in leaves alongside mild curling: Flea beetles. Usually minor; tolerate or treat with kaolin.
- Grey-brown patches, fluffy mould on leaves after a wet cut-back: Botrytis. Improve air circulation, remove affected material.
- Crown blackening, whole plant collapsing with wet soil: Root rot. Improve drainage immediately.
Cause 1: Aphids
Aphid attack is the most common reason for catmint shoot tips curling downward in spring. The main culprit is Myzus persicae, the glasshouse and peach-potato aphid, though other generalist aphid species also colonise Nepeta. Colonies are pale green and cluster on the soft new growth and shoot tips as the plant breaks dormancy and puts out its first flush of growth, typically from April onward.
The leaves curl downward and inward around the colony, and you will find the insects on the undersides of the curled leaves and packed along the growing tip. The sticky residue they leave (honeydew) can develop a layer of sooty mould that blackens the affected foliage further. Growth slows and the shoot tips look bunched and matted.
Aphid pressure on catmint is typically worst in April and May, before ladybird, lacewing, and parasitic wasp populations build up to natural control levels. By June the plants are usually flowering strongly and aphid damage becomes inconspicuous. The plants recover well from spring aphid attack and it rarely affects the quality of the first flowering flush.
How to fix it. Blast aphid colonies off with a strong jet of water from a hose, directing it at the underside of the curled tips. Repeat every two to three days for a fortnight. For persistent infestations, apply insecticidal soap or a pyrethrin-based spray, coating both leaf surfaces. The aromatic compounds in catmint foliage attract hoverflies, parasitic wasps, and other beneficial insects, so avoid systemic or broad-spectrum insecticides that will knock back the natural predator community.
Cause 2: Powdery mildew
Powdery mildew is the signature disease of catmint in UK gardens. The fungus responsible is Erysiphe nepetae (and closely related Erysiphe species). It produces a white, floury or powdery coating on the leaf surface, typically starting on the older leaves lower in the plant and spreading upward. The affected leaves curl, distort, and eventually look washed-out and grey. The plant loses its characteristic fresh, silver-green appearance and looks dull and flat.
Mildew on catmint is almost always a problem of the post-flowering period. Once the first flush of lavender-blue flowers fades in June or July, the plant's growth slows and the dense, low mound of foliage traps humid air in its interior. Warm days and cool nights in late summer create the moisture gradient on leaf surfaces that powdery mildew spores need to germinate. The disease is worse in sheltered, enclosed garden positions and on plants growing in rich, fertile soil that produces soft, lush growth.
It is worth noting that catmint leaves are naturally grey-green due to fine surface hairs, so the white mildew coating can be subtle at first. The diagnostic sign is the powdery texture you can rub off with a finger, together with the curling and distortion of the affected leaves.
How to fix it. The traditional cut-back is by far the most effective response. Using shears or hedging scissors, cut the entire plant back to approximately 8 cm (3 inches) above the ground immediately after the first flowering flush declines. This single action removes all mildewed growth, opens the crown to air, and signals the plant to push a fresh flush of growth from the base. In four to six weeks you will have a neat mound of clean new foliage and, typically, a generous second wave of flowers in late August and September. The cut-back is standard practice for all Nepeta x faassenii types and is part of normal catmint maintenance rather than a remedial measure.
If you want to suppress mildew before cutting back, spray with a potassium bicarbonate solution or neem oil at the first sign of the white coating. These treatments slow the spread but do not reverse damage already done to individual leaves. Plant catmint in full sun with at least 40 cm between plants to maximise air movement through the crown.
Cause 3: Cat damage
The name catmint is not coincidental. Cats are strongly attracted to the nepetalactone compounds in Nepeta foliage, and they roll in, sit on, chew, and generally flatten the plants. Nepeta cataria (catnip) produces the highest concentrations of these compounds and is particularly irresistible; most hybrid catmints including N. x faassenii 'Walker's Low' also attract cats, though somewhat less intensely.
Physical damage from cats produces curled and bruised leaves, crushed stems, broken flower spikes, and disturbed soil around the crown. The bruised leaves often take on a darker green colour before browning at the edges. Unlike aphid or mildew damage, there are no insects or fungal signs to find, and the damage pattern is irregular and mechanical rather than systemic.
How to fix it. Established clumps of N. x faassenii and its cultivars are robust enough to tolerate regular cat visits and bounce back after each episode of rolling. New plantings are more vulnerable and can be permanently set back by intense cat attention. Surround new plants with a low cage of chicken wire or a ring of bamboo canes pushed into the soil close to the crown until the plant is large enough to withstand it. Some gardeners plant N. cataria at the garden perimeter as a deliberate decoy to draw cat attention away from other plantings.
Cause 4: Flea beetles
Flea beetles (Phyllotreta species and related genera) create small, round shot-holes in catmint leaves, typically 1 to 3 mm in diameter. The combination of these holes with mild leaf curling at the margins can cause concern. Flea beetles are small (1 to 3 mm), shiny, and jump rapidly when disturbed, which is the characteristic behaviour that gives them their name.
Damage on established catmint is almost always cosmetic. The plants are vigorous enough that flea beetle feeding rarely slows growth or reduces flowering. On seedlings or very young transplants, heavy flea beetle pressure in dry spells can be more damaging.
How to fix it. Tolerate minor flea beetle damage on established catmint; the plants outgrow it quickly. For severe infestations on young plants, apply kaolin clay dust to the foliage as a physical deterrent, or use a pyrethrin spray in the evening to reduce impact on pollinators. Keeping transplants well-watered during establishment makes them less vulnerable, as flea beetles prefer stressed, dry plants.
Cause 5: Botrytis and root rot
Two further causes of leaf curl and deterioration are worth knowing in damp UK conditions. Botrytis (grey mould, Botrytis cinerea) can develop on catmint after a wet cut-back if the cut stems sit in humid, still air without drying quickly. The mould colonises cut stem surfaces and can spread to adjacent leaves, causing grey-brown patches and leaf curl on regrowth. The fix is improved air circulation and, if the infection is extensive, removing the worst-affected stems at soil level and disposing of them in the bin rather than the compost.
Root rot develops in waterlogged or persistently wet soil and is particularly damaging because catmint is a Mediterranean native adapted to fast-draining, lean conditions. The first signs are yellowing and curling of the lower leaves followed by collapse of the whole plant, with the crown turning black and soft at soil level. Improve drainage before planting by incorporating coarse grit into clay soils. Catmint in the right conditions (full sun, free-draining, low-fertility soil) rarely develops root rot even in wet UK summers.
Keeping catmint healthy long-term
Catmint rewards a fairly minimal care approach. The key practices that keep it free of the problems above are: cut back hard after the first flowering flush every year; grow it in full sun in poor, free-draining soil and avoid adding compost or fertiliser around it; space plants generously to allow air to move through the crown; divide congested clumps every three to four years in early spring to refresh the root system and reduce disease pressure. These steps keep the plant in vigorous growth, reduce mildew and botrytis risk, and ensure the second flush of late-summer flowers that makes catmint such valuable planting in UK borders.
As a bonus for gardeners, the strong pollinator value of catmint means bees, bumblebees, and butterflies will be active around the plant throughout both flowering periods. This same beneficial insect community provides a degree of natural aphid control as the season progresses, making catmint largely self-regulating once established in the right position.
Frequently asked questions
Why are my catmint leaves curling?
The two most common reasons catmint leaves curl are aphids in spring and powdery mildew from midsummer onward. In spring, colonies of pale green aphids (mainly Myzus persicae) cluster on soft shoot tips and cause the growing tips to curl downward. From midsummer, powdery mildew (Erysiphe nepetae) produces a white powdery coating on the leaves alongside curling and distortion. Other causes include cats rolling in and bruising the plant, flea beetle feeding holes, botrytis after a wet cut-back, and root rot in waterlogged soil.
Why are my catmint leaves curling and turning white or grey?
A white or grey powdery coating on catmint leaves that are curling and distorting is powdery mildew. The fungus thrives in warm, dry air after the plant's first flowering flush in June or July, and is especially common in sheltered positions with poor air circulation. Cut the entire plant back to about 8 cm above ground immediately after the first flowers fade. This removes all mildewed growth and triggers a flush of clean new foliage and a second wave of flowers in late summer. Note that catmint leaves are naturally grey-green from surface hairs; the diagnostic sign is the powdery texture that rubs off on a finger.
Can cats cause catmint leaves to curl?
Yes. Cats are strongly attracted to the nepetalactone compounds in Nepeta foliage, especially in N. cataria (catnip), and they roll in, sit on, and chew the plants. Rolling causes physical flattening, bruising, and stem breakage; the bruised leaves curl, wilt, and brown at the edges. If cats are the culprit you will see obvious mechanical damage (crushed stems, broken flower spikes, disturbed soil) with no insects or fungal signs present. Established clumps of N. x faassenii recover quickly; protect new plantings with chicken wire until the plant is large enough to withstand cat visits.
How do I stop catmint getting powdery mildew every year?
The most effective long-term prevention is the traditional cut-back: shear the entire plant hard to about 8 cm after the first flush of flowers fades in June or July. This removes mildew-prone older growth, opens the plant up to air, and triggers fresh healthy regrowth. Plant catmint in full sun with at least 40 cm spacing between plants to maximise air movement. Avoid rich, fertile soil or excessive watering, which produce lush, soft growth more susceptible to mildew. Divide congested clumps every three to four years in early spring to maintain vigour and improve air movement through the crown.
Why are the tips of my catmint curling and matted with insects?
Curled, matted shoot tips covered in small pale green insects are a sign of aphid infestation, most likely the glasshouse and peach-potato aphid (Myzus persicae). Aphids colonise the soft new growth in spring, sucking sap and causing leaves to curl downward around the colony. You may also see sticky honeydew residue and sooty mould on affected growth. Blast aphids off with a strong jet of water, repeating every two to three days. Aphid populations typically crash naturally by early summer as ladybirds, lacewings, and parasitic wasps build up alongside the catmint's first flowering flush.