Geranium thunbergii aka Thunberg's Geranium

Geranium thunbergii is a perennial in the geranium family, Geraniaceae. Its common names include Japanese cranesbill and Thunberg's geranium. It comes from temperate parts of eastern Asia. Its range includes China, Korea, Japan, Taiwan and the Kuril Islands. In Japan, it grows in grassy places at low elevations. It is not native to Britain or Ireland.

This semi-evergreen plant has stems that trail or rise upward. It grows about 1 foot [0.3 metres] tall. The RHS gives an upper garden height of 1.6 feet [0.5 metres]. Its spread can also reach 1.6 feet [0.5 metres]. Plants reach their full size within two to five years. The light green leaves have lobes with bronze marks in their notches. Small flowers grow in loose groups above the leaves. They may be pink, purple or white, with purple veins. Bloom starts in late summer and may last into early autumn.

Grow this plant in sun or partial shade. It does well in sun where soil drains freely. It accepts clay, chalk, loam and sand. Acid, neutral and alkaline soils all suit it. Moist soil is suitable, but the roots must not stay waterlogged. The RHS rates its winter hardiness as H5. Plants For A Future lists USDA zones 6–9. It suits both open and sheltered sites. Its tolerance of varied sites gives gardeners some choice in placement.

Use it in borders, cottage gardens or informal beds. The RHS also lists coastal sites and wildlife gardens as suitable settings. It can grow beneath roses and shrubs. Its trailing stems sometimes form roots where nodes touch soil. Grow new plants from seed or divide existing clumps. Remove spent flower stems and old leaves to prompt fresh growth. Watch for slugs, snails, capsid bugs and geranium sawfly larvae. Vine weevil larvae may also attack it. Downy mildew and virus diseases can occur. Dry conditions may bring powdery mildew.

Plants For A Future lists young leaves as edible. It gives no details on how to prepare them. Older leaves, gathered at peak growth, serve as a tea substitute. That source gives the plant a low food-use rating. It also records astringent use of the whole plant. Its medicinal-use rating is low as well. Plants For A Future reports no known hazards. This is not proof of safety for every use or pet.