Wild Mint

Wild mint, also called horsemint (Mentha longifolia), is a vigorous, rhizomatous perennial in the mint family (Lamiaceae), native to Europe, western and central Asia, and parts of Africa.134 It is aromatic, edible, and medicinally used, and like other true mints it spreads readily from underground rootstock.13 For a homesteader the appeal is simple: it is one of the easiest perennials to establish in a damp corner, multiplying from the smallest scrap of healthy rootstock and giving a strongly minty, cut-and-come-again harvest along stream banks, ditches, and other moist ground where thirstier herbs sulk.12

This is a fast-growing, spreading perennial that typically reaches 0.5 to 1 m tall, occasionally up to 1.5 m in very favourable conditions and shorter on dry sites.1 The stems are erect, square in cross-section as is typical of the mint family, and often branched.12 Leaves are arranged in opposite pairs, narrowly lanceolate to oblong (the “long leaves” that give the species its name longifolia), and characteristically stalkless (sessile) — a key feature that separates it from other wild mints.1 The foliage is hairy with a somewhat rough, felted texture, green to grey-green, toothed along the margins, and carries a strong, musty-minty aroma when crushed.12

Growing wild mint

Wild mint grows in marshes, along streams, and in other moist places, and in cultivation it does best in moist but well-drained soil.13 It is strongly associated with riparian zones and damp grassland across its native and naturalised range, so the obvious place for it is the wettest, lightly shaded ground on the property — the edge of a channel, a pond margin, or a sunken bed.13 It is also notably cold-hardy: the Royal Horticultural Society rates it Hardiness H7, meaning it tolerates very cold winters (at least around −20°C), which corresponds roughly to USDA zone 5 and colder, though no specific USDA figure is given in the primary sources.3

Propagation is easy to the point of needing restraint:

• Division: The simplest method. Wild mint is easy to multiply by division — the smallest piece of healthy rootstock quickly grows into a new clump with regular water and compost.1 For mints generally, division can be done in spring or autumn.3
• Cuttings: Cuttings of young, actively growing shoots root easily throughout the year.1

Because it runs on creeping rhizomes and spreads vigorously, plant it where a path, a hard edge, or a channel will check its travel, or lift and divide it regularly to keep it in bounds.13 Detailed plant spacing and time-to-maturity figures are not consistently documented in the general botanical sources here, so they are left out rather than stated with false precision; in practice treat it as a fast-spreading groundcover that fills in on its own once established.1

Harvest and uses

The harvest is the aromatic top growth: the hairy, sessile leaves and tender stems, cut as needed through the growing season.1 Wild mint flowers in summer — recorded as mid- to late summer in the UK, and from November to April in the southern-hemisphere summer in southern Africa — producing long, tapering spikes of densely packed small tubular flowers in white to mauve or pale purple.13 Cut the foliage before or during flowering, when the leaves are most strongly scented, and the plant resprouts from its runners for repeated harvests.1

It is an edible, aromatic herb with a strong mint, peppermint-like scent, used both as a flavouring and as a traditional medicinal plant.13 Beyond the kitchen, its spreading habit makes it useful as a living mat on damp, lightly shaded ground, so it doubles as a low-maintenance groundcover for moist edges.13 A note on names: in North America “wild mint” more often refers to a different species, Mentha arvensis, which has stalked (petiolate) leaves and a different flower arrangement; M. longifolia is distinguished by its sessile long leaves and long, dense white-to-mauve flower spikes.134

Safety and cautions

Wild mint is edible and medicinally used, but its essential oil is chemically potent.15 The sources are explicit that internal medicinal use requires medical supervision because of possible toxicity and the potential for drug interactions.15 This profile describes traditional and culinary use only and makes no claim that the plant treats or cures any condition. Concentrated extracts and essential oils are far stronger than the fresh leaf used as a flavouring, so anyone who is pregnant or breastfeeding, and anyone taking prescription medication, should seek qualified medical advice before using it medicinally.15

Sources

1. Mentha longifolia — PlantZAfrica, South African National Biodiversity Institute (SANBI)
2. Mentha longifolia (L.) L. — Global Biodiversity Information Facility (GBIF)
3. Mentha longifolia — Royal Horticultural Society (RHS)
4. Featured Plant: Wild Mint — Minnesota Board of Water & Soil Resources
5. Mentha longifolia: overview — ScienceDirect Topics