Corn mint

How to recognise it

Growth habit

Perennial with sprawling to ascending, often branched stems of 10–50 cm and creeping rhizomes.

Leaf

Opposite, oval to elliptic, 2–6 cm, scalloped to toothed, short-stalked and hairy. Smells of mint when crushed, but rather musty.

Flower

Small lilac, sometimes white, two-lipped flowers of 3–5 mm in dense, rounded whorls in the leaf axils, spread along the stem. The stem ends in a pair of leaves, not in a flower head. From July to October.

Stem

Square, hairy and often tinged red.

Fruit/Seed

Four small, smooth nutlets per flower, inside the hairy, bell-shaped calyx with short, triangular teeth.

Confusion with

Water mint has a rounded flower head at the top of the stem and a stronger scent. Whorled mint, a hybrid of corn mint and water mint, has a calyx with long, pointed teeth. Gypsywort also has flower whorls in the leaf axils, but tiny white flowers, deeply cut leaves and no mint scent.

Flowering: July–October · Pruning: March and June

Why grow it?

• Flowers late, from July to October, when many other wild flowers are over.
• Bees, bumblebees, hoverflies and butterflies visit the flower whorls.
• A food plant for the caterpillars of the mint moth, a small purple-and-gold moth that flies by day.
• A natural ground cover for a damp spot: beside a pond, by a wildlife pool or in a wet corner of the garden.
• You can use the leaves in the kitchen like other mints, although the flavour is less fine.

Corn mint: where does it grow best?

• In the wild: damp arable fields and stubbles, wet grassland, the banks of ditches and ponds, wheel ruts and damp woodland paths.
• Sun to part shade.
• Moist to wet, fertile soil: loam, clay or sand; tolerates temporary flooding.
• In the garden: beside a pond or pool, in a wet corner, at the edge of a small bog garden or in a large pot.

Goes well with

• Ragged-robin: Pink flowers in spring, on the same wet ground.
• Water forget-me-not: Small pale blue flowers at the water’s edge.
• Purple-loosestrife: Tall purple spikes above it, in the same damp zone.
• Meadowsweet: Creamy plumes in summer, for a damp wild patch.

Corn mint: when and how to plant it?

1. Buy plants from a nursery for native or pond plants, and ask for true corn mint, not a hybrid.
2. Plant in April–May or September, 30–40 cm apart, in moist soil.
3. To keep it in check, plant it in a bottomless bucket or large pot sunk into the ground up to the rim.
4. Water regularly for the first few weeks, until it is well rooted.
5. You can also sow it: scatter the fine seed in spring on moist seed compost in a pot and do not cover it, as it needs light to germinate.
6. Never dig up plants from the wild; a nursery plant or a cutting from someone nearby is a better start.

Care

Watering

Keep the soil moist. Water in dry summer spells, or the leaves dry out.

Feeding

Not needed; on soil that is too rich it goes floppy and is more prone to rust.

Spreading

It spreads by underground runners. Chop off the edges with a spade every spring or keep it in a sunken pot.

Mowing

In a damp hay meadow it copes well with mowing. Mow the part where it grows only after flowering, or leave a strip uncut.

Harvesting

Pick young tips from May to September; this also keeps the plant compact.

Tip: Plant corn mint in a large bottomless pot sunk into the ground up to the rim: it stays in its place, and you can easily keep the soil around it moist.

Pruning and mowing

Pruning months: March and June.

When: In March, cut away the dead stems; in June, cut back by half for fresh leaves if you wish.

How:

• Leave the faded stems standing over winter: small insects overwinter in them.
• In March, cut them to just above the ground, before the new shoots appear.
• For fresh leaves, cut the plant back by half in June; it soon regrows and flowers afterwards.
• Cut stems with rust down to the ground straight away.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Cuttings

From May to August, put shoot tips of 8–10 cm in a glass of water or moist cutting compost; they root within a few weeks.

Division

In March–April or September, chop off a piece of rhizome with shoots and replant it elsewhere.

Seed

Sow in spring on moist compost, uncovered. Cuttings are quicker and guarantee true corn mint.

Corn mint: how does it get through the winter?

Hardy to −30 °C.

• The stems die back in autumn; the plant overwinters as rhizomes in the soil.
• The dry stems give shelter to small insects in winter.
• Fully hardy; new shoots appear early in spring.

Diseases and pests

• Mint rust: Orange to brown pustules on leaves and stems, sometimes with distorted shoots in spring. Cut off affected parts straight away and put them in the household waste.
• Spreading: The rhizomes run far. Use a sunken pot or chop off the edges every year.
• Powdery mildew: White powder on the leaves in dry summers. Water at the base and cut back affected stems.
• Hybrids: Next to water mint, hybrids form easily. Propagate by cuttings if you want pure plants.

Through the year

• March: Cut down old stems. Chop off the edges.
• April: Plant or divide. New shoots.
• May: Pick tips. Take cuttings.
• June: Cut back by half for fresh leaves if you wish. Water in dry spells.
• July: First flower whorls. Bees and hoverflies.
• August: Full flower. Watch for rust.
• September: Flowering. Plant or divide.
• October: Last flowers. Leave the stems standing.
• December: Dormant underground.

Did you know?

• In Greek mythology, Minthe was a nymph turned into a plant by a jealous Persephone; the name Mentha is said to come from her.
• In Asia, a closely related mint, sometimes treated as a form of corn mint, is grown on a large scale as a source of natural menthol.
• Where corn mint and water mint grow together, their hybrid, whorled mint, often appears, with features of both parents.