Mentha longifolia Seeds | Horsemint
LATIN NAME: Mentha longifolia
COMMON NAME: Horsemint
Plant Profile
Mentha longifolia is the mint of riverbanks and irrigation ditches, taller and looser than the garden mints and far more variable. The leaves are long and narrow, grey-green and softly hairy underneath, with a serrated edge and almost no stalk. The plant runs on white rhizomes just below the surface and forms patches a metre or more across in a season.
Flowers are carried in a dense cylindrical spike rather than in the whorls of spearmint, and they open from the bottom upwards over several weeks, which is why the plant is good for bees. In the Middle East and the Balkans it is gathered from wild stands for tea, and the scent varies from clean peppermint to a harsher, almost medicinal note depending on the population and the water it grew in.
Science & Biotechnology
The oil is dominated by menthone and pulegone rather than by menthol, and that profile is the reason the plant is not a substitute for peppermint in commerce. Pulegone is the compound of concern: it is metabolised in the liver to a reactive intermediate, and high intakes have caused injury in animal studies. Spearmint carries almost none, peppermint carries little, and some horsemint populations carry a great deal.
The plant is also a natural hybrid complex. Mentha longifolia crosses with M. suaveolens, M. spicata and others wherever their ranges overlap, and the offspring are often fertile, so a stand can contain a range of chemotypes that look identical. Oil buyers test by gas chromatography rather than by leaf shape, because the leaf tells you almost nothing about the chemistry.
Uses & Benefits
In Jordan, Lebanon and Egypt the dried leaf goes into tea, usually with sage or with black tea, and it is drunk hot in the evening. In the Balkans it is used to flavour bean dishes and cheese, and the fresh leaf is chopped into salads where spearmint would be too sweet.
The leaf is also a traditional carminative and a wash for insect bites, and the oil has been used in toothpastes and in chewing gum at low levels. Anyone using it as a daily infusion should rotate it with other mints, because the pulegone load of a wild-gathered plant is unpredictable and a garden clone is not.
Growing from Seed
Seed is viable but variable, and a packet will give plants with a range of scents and habits. Sow on the surface in spring, since the seed needs light, keep it at 18 to 20 degrees, and prick out when the first true leaves appear. Named forms are better raised from cuttings or by division, because seed does not fix the chemotype.
The plant wants moisture and will take a wet corner that kills other herbs. It spreads by rhizome, so sink a barrier or plant it in a bottomless bucket if space is tight. Cut it back after flowering to keep the leaves tender, and divide the clump every third year, since old crowns go woody and the centre dies out.
Our Take
A rough, generous mint for wet ground and wild tea, not a replacement for peppermint. Use it fresh and do not drink it daily.
Related Reading
If Horsemint appeals to you, these related plants are worth a look: