Culture
Easily grown in average, medium to wet, well-drained soils in full sun to light shade. Tolerant of occasional flooding. Also tolerates poor, sandy, somewhat dry soils. May spread by self-seeding and/or suckers to form thickets. It is considered weedy/invasive in some parts of its range, particularly in the northeastern and northwestern U.S. Prune in late winter to early spring for purposes of improving shrub form.
Noteworthy Characteristics
False indigo is a deciduous shrub that typically grows to 4-12' (less frequently to 20') tall with a spread often in excess of its height. It is native to moist open woodland areas, floodplains, stream banks and swamp margins from central to eastern Canada south throughout much of the U. S. into northern Mexico. It features compound, odd-pinnate leaves (each to 12" long). Each leaf contains 11 to 35 spiny-tipped, oval to elliptic, dull gray-green leaflets (to 2" long) with glandular dots and toothless margins. Tubular scented flowers (each to 3/8" long) bloom in May-June in dense, spike-shaped clusters (racemes) to 8" long. Each flower has a single-petaled purple corolla and 10 protruding stamens with showy orange-yellow anthers. Flowers are followed by fruits in small, resinous-dotted, 1-2 seeded pods (to 1/2" long) which mature in July and August. This shrub grows much larger than Amorpha canescens (lead plant).
Genus name comes from the Greek word amorphos meaning shapeless or deformed in reference to the corolla of this pea family genus lacking wings and a keel.
Specific epithet comes from the Latin word frutex meaning shrub in reference to its shrubby form.
Plants contain indigo pigment, but in quantities too small for commercial use (hence the common name of false indigo).
Problems
No major pest or disease problems. Some susceptibility to leaf spot, powdery mildew, twig canker and rust.
Uses
False indigo has attractive flowers. It is often used for erosion control, windbreaks and screens. Good shrub for moist naturalized areas or areas with poor soils.