Amorpha fruticosa aka False Indigo

Amorpha fruticosa, or false indigo, is a deciduous shrub. It belongs to the bean family, Fabaceae. RHS and NC State place its origin in the southern United States. PFAF describes a wider wild range into Canada and northern Mexico. It grows beside streams, ponds, and swamps, and in open woods. It also occurs on floodplains, gravel bars, and roadsides.

This fast-growing shrub forms a broad clump with many stems. RHS gives a garden height and width of 8–13 feet [2.5–4 metres]. NC State lists plants reaching 15 feet [4.6 metres] in both dimensions. Seeds and suckers help it spread into dense thickets. Its width can exceed its height. Smooth gray bark covers the woody lower stems. Upper stems are dull green, while twigs turn gray-brown. Leaves cluster near the tops of the stems. The pinnate leaves bear many oval leaflets with smooth edges. Their upper sides are dull green, with paler undersides. Leaves can turn yellow in fall before they drop.

Deep purple flowers form narrow racemes at the branch tips. Orange or yellow anthers stand out against the petals. Each flower has just one petal, unlike many bean-family flowers. The fragrant clusters reach about half a foot [0.15 metres] long. Missouri Botanical Garden gives April to June as the bloom season. Virginia Tech reports flowers in midsummer, so timing varies. Flowers open from the bottom of each cluster upward. Small green pods turn brown as they dry. Bees and butterflies visit the blooms for nectar. Several butterflies and skippers use the leaves as larval food.

Grow false indigo in full sun or partial shade. It accepts sandy, loamy, and clay soils, including poor ground. It tolerates acid, neutral, and alkaline conditions. Moist sites suit it, but it also withstands drought and wet soil. Sources rate it for USDA zones 4–9 and UK H6. It needs little upkeep. Garden uses include screens, windbreaks, and soil erosion control. Pond edges and broad natural plantings suit its spreading form.

Pests seldom cause serious trouble, but some diseases can occur. These include leaf spot, mildew, rust, and twig canker. Its spread can make it weedy. NC State calls it inedible, while PFAF records crushed fruit as a condiment. PFAF also warns of possible poisoning in livestock. These conflicting reports do not establish safe food use.