Indigofera heterantha aka Himalayan Indigo

Indigofera heterantha, or Himalayan indigo, belongs to the pea family. Its native range runs from Afghanistan to Tibet and northern Myanmar. It also grows across parts of the Himalaya. Wild plants grow on dry, sunny slopes and in forests. On some slopes, they form thick scrub. Gardeners grow this deciduous shrub for its leaves and summer flowers.

The shrub has an open, rounded shape. Height and width are often much the same. NC State gives both as 4–6 feet [1.2–1.8 metres]. RHS gives a larger range of 5–8 feet [1.5–2.5 metres]. Plants take five to ten years to reach full size. Cold conditions can kill the top growth back each year. New shoots may then reach 4 feet [1.2 metres] in one season. The pinnate leaves have 13–21 small leaflets. Their shades range from grey-green to blue-green. Leaves grow alternately along the stems and lack striking autumn colour.

Flowers start in early summer and bloom during summer. The small, pea-shaped flowers range from pink to rosy purple or lilac. They grow in upright racemes about 0.25–0.42 feet [0.08–0.13 metres] long. Each flower measures about 0.04 feet [0.012 metres]. Dark purple legume pods follow the flowers. These fruits appear in summer and autumn. The flowers provide the main seasonal display, while the pods add later interest.

Choose full sun and soil that drains well. Afternoon shade can help in hot, humid places. The shrub grows in clay, loam, sand, and chalk. It accepts acid, neutral, and alkaline soils. Moist soil suits it, though it also tolerates drought and heat. RHS rates it H5 for UK hardiness. NC State lists USDA zones 5a–8b. Use it in borders, hedges, or as an accent. It also suits banks, slopes, and wall-side beds. Propagate it from seed or semi-hardwood cuttings. Hard pruning in spring is an option when needed.

RHS reports few pest problems. Honey fungus may affect plants where the fungus occurs. The degree of risk remains unclear. Plants For A Future records flowers as food after boiling and pickling. That source lists no known hazards, but this does not establish safety for pets. It records no medicinal use. People use the branches for baskets, twig bridges, and fuel. The plant also fixes nitrogen.