Mint (Mentha) is a hardy perennial herb that spreads so vigorously by underground runners that it can overrun a bed within a season or two. Grow it in a large pot, or plant it in the ground inside a bottomless bucket or root barrier sunk 25–30 cm deep. Plant young plants from spring into moist, humus-rich soil in partial shade or sun; in full sun it needs more frequent watering, as it wilts quickly when dry. Peppermint, spearmint and apple mint differ in flavour, and seed-raised plants are rarely true to type, so buy named plants or take cuttings. Pick shoot tips regularly to keep plants bushy. The leaves are most aromatic just before flowering, which is the best moment to cut a larger amount for drying or tea. Rust – orange spots on the leaves – is the most common problem; cut affected plants to the ground and dispose of the foliage. Divide and replant pot-grown mint every two or three years, as the centre dies out.