Mentha aquatica aka Water Mint

Mentha aquatica, or water mint, belongs to the mint family, Lamiaceae. Its native range spans Africa, Europe, western Asia and central Siberia. It is native to Britain and Ireland. This perennial grows in marshes, fens, wet woods and swamps. It also grows beside rivers, streams and ponds. These wet sites suit its role in water gardens.

The RHS gives a garden height of 0.3–1.6 feet [0.1–0.5 metres]. Its plant account also records heights of 3 feet [0.9 metres]. Plants spread 1.6–3.3 feet [0.5–1 metre] across. Long, thin rhizomes spread through the soil and form new shoots. The stems often show red or purple tones. Dark green leaves give off a strong mint scent. The plant sheds its leaves rather than keeping them year-round.

Small pink-purple flowers open in summer. They form rounded spikes at the tips of stems. Full sun helps the plant flower well. Water mint also grows in partial shade. Its scented leaves and summer flowers suit pond edges and wildlife gardens. Containers offer another way to grow it where wet conditions suit. Its spreading habit needs care in a planted pond.

Grow water mint in muddy margins or pond baskets. The RHS allows water depths up to 0.8 feet [0.25 metres]. It accepts clay or loam and needs wet, poorly drained soil. Acid, neutral and alkaline soils all suit it. The RHS rates it H6, while PFAF lists USDA zones 5–9. Divide plants in spring and cut them back after flowering. Plants can become a nuisance without control. The RHS reports few pest problems. Powdery mildew or mint rust may occur when plants get too dry.

The leaves can be eaten raw or cooked. They can flavour salads, cooked dishes and herbal tea. Their strong taste may be too sharp for some people. PFAF records traditional use of leaf tea for headaches, fevers and digestive complaints. It also records use in mouth rinses and gargles. These uses do not establish that treatments work or are safe. The scented plant has served as a strewing herb and pest repellent. PFAF reports no toxicity records for this species. That lack of records does not establish safety for every use.