Mentha spicata aka Spearmint

Mentha spicata, or spearmint, is a perennial herb in the mint family. Its native range runs from Europe to China. It grows in damp fields and beside ponds and lakes. Gardeners grow it for its scent and food uses. Its leaves fall away during the dormant season. The plant grows fast and can form wide colonies.

Size varies between garden sources. NC State gives heights and widths of 1–2 feet [0.3–0.6 metres]. RHS gives heights of 1.6–3.3 feet [0.5–1 metre]. Its spread can reach 3.3–4.9 feet [1–1.5 metres]. Upright stems have four sides and may bear hairs. They can take root where they touch the soil. Underground rhizomes also help the plant spread. Bright green leaves have pointed tips and toothed edges. They have little hair and almost no leaf stalk. Their strong scent matches their clear spearmint taste.

Small flowers grow in narrow spikes at the stem tips. Their shades range from pale purple to pink or white. NC State records bloom from July through October. RHS describes a summer bloom season. Butterflies visit the flowers. Each flower can yield four small nutlets in autumn. The plant suits herb beds, pots, and informal gardens. Its spreading habit can provide ground cover in damp sites.

Grow spearmint in sun or part shade, with moist soil. It thrives in rich soil with good drainage. It accepts clay, loam, sand, and chalk, across a broad pH range. Dry soil does not suit it. Water new plants while they settle in. Pots also need water in summer. A deep pot or root barrier helps limit spread. Divide pot-grown plants every few years. Picking young shoots helps keep growth bushy. Seed and division offer ways to raise new plants. Sources list USDA zones 4–9 and UK hardiness H7.

Rust, leaf spot, and powdery mildew can affect the leaves. Leafhoppers, mint beetles, and caterpillars may also cause damage. Fresh or dried leaves and flowers flavour tea, sauces, sweets, and drinks. Spearmint also supplies oil for food flavouring and oral care products. Leaf tea has traditional uses for headaches and digestive complaints. These uses do not establish medical benefit. Despite its food uses, large amounts can cause vomiting and diarrhoea. Its essential oil can be toxic in high doses. NC State also flags risks for cats, dogs, and horses.