1283 Amorpha fruticosaCommon Names: false indigo,bastard indigo,false indigo bush Family: Fabaceae (bean Family)
False indigo is a fast growing open and airy shrub that can get up to 10-15 ft (3-4 m) tall, with a similar spread. However, it is more typically around six feet (2 m) tall and spreading a little more than that. False indigo has deciduous pinnately compound leaves around a foot (30 cm) long, each with 13-33 oval or oblong leaflets. Individual leaflets are 1-2 in (2-5 cm) long and about a half inch (12 mm) wide. The inflorescence is a slender six inch (15 cm) long tightly packed cluster of bright purple flowers with conspicuous orange anthers. The flower clusters are held erect near the ends of the branches and above much of the foliage. A close look at a single flower reveals that it has only one petal with ten stamens, each topped with a bright orange anther and extending well beyond the petal. The fruits are small flattened seedpods (legumes) about a quarter inch (60 mm) long, each containing 1-2 seeds. The pods have tiny dotlike glands.
A handful of cultivars have been selected. A weeping form, ‘Pendula’; a white flowered form, ‘Albiflora’; and one with crinkled leaves, ‘Crispa’ are listed.
Amorpha fruticosa occurs in almost the entire United States and southern Canada. It is a characteristic component in open wetlands, stream banks, swamp edges and bogs. False indigo is cultivated as an ornamental and occasionally escapes, naturalizing in the wild.
Prune false indigo in late winter or early spring to maintain a pleasing shape, otherwise it tends to get leggy and sloppy. Light: False indigo thrives in full sun and does well in light shade, too. Moisture: Although false indigo usually is encountered growing on a river bank or the edge of a swamp, once established in cultivation, it is quite tolerant of dry conditions. False indigo likes a well drained, sandy soil but can tolerate periods of flooding. Hardiness: USDA Zones 4 - 9 . Propagation: Rooted suckers from the base of the plant can be separated to start new plants. Stem tips can be rooted fairly easily. Seeds have a hard coating and can take a long time to germinate. Still, false indigo can self seed and may even form a thicket.
The flowers of false indigo are very showy, and the shrub works well in informal mixed shrub borders or for naturalizing in wildflower/shrub gardens. False indigo tolerates poor sandy soils, dry soils, limey soils, acidic soils and soils that get flooded occasionally. False indigo is sometimes used for erosion control and makes an excellent addition to a rain garden. Without remedial pruning, false indigo can become a leggy and ungainly shrub with most of its foliage concentrated near the top.
Butterflies nectar at false indigo flowers and the caterpillars of several species dine on the leaves. The flowers are pollinated by various kinds of bees.
This native American makes a great substitute for the Chinese butterfly bush (Buddleja davidii).
Under ideal growing conditions, false indigo can become weedy and even invasive, and is considered so in parts of New England and the Northeast. No doubt some portions of its very wide distribution can be attributed to escapees from cultivation.
Steve Christman 3/28/17