Cardamine amara aka Large Bittercress

Cardamine amara, or large bittercress, belongs to the cabbage family, Brassicaceae. Its native range spans Europe, western Siberia and Türkiye. It is native to Britain and Ireland too. The Welsh name is chwerw mawr. This perennial grows to about 2 feet [0.6 metres] tall. It comes from temperate regions and grows in wet habitats.

In the wild, it grows beside springs and streams. It also occurs in fens and places with trickling water. It can dominate the ground layer in alder woods. These sites have damp ground with water moving through it. Plants favour peaty soil in these habitats. For gardens, this makes it a choice for bog planting. A wild garden also gives it room to spread.

Flowers appear from April to June, with seeds ripening from May to September. Each flower has both male and female organs. Bees, flies and beetles pollinate the flowers. Moths and butterflies also visit them for pollination. The plant is self-fertile, so it can set seed alone. It spreads freely through self-sown seed and may become intrusive. Its spread needs thought when choosing a place in a garden.

Grow it in moist soil with plenty of humus. It prefers shade or part shade, though it can grow without shade. Sandy soil, loam and clay can all support it. It accepts mildly acid, neutral and mildly alkaline ground. The key need is moisture rather than one soil texture. Plants For A Future describes it as easy to grow. It reports hardiness to at least −20°C and USDA zones 4–8. Sow seed in its final outdoor spot in April. Choose a shady place for sowing.

The leaves are edible raw and have a sharp, cress-like taste. They also have some bitterness. Small amounts can add flavour to a salad. In most years, leaves remain available throughout the year. Plants For A Future lists no known hazards for this species. That report does not establish safety for every person or pet. The same source records medicinal uses, including diuretic and stimulant uses. It also records use against scurvy, but gives no treatment guidance. These recorded uses do not establish that home treatment works.