Amorpha fruticosa
false indigo bush
Overview
Amorpha fruticosa is a deciduous shrub in the pea family reaching 6-12 feet (1.8-3.7 m) tall and 6-10 feet (1.8-3 m) wide, with an open, multi-stemmed, upright form. The pinnately compound leaves measure 4-12 inches (10-30 cm) long and carry 11-25 oval leaflets, each 0.5-1.5 inches (1.3-3.8 cm) long, medium green and dotted with tiny resin glands that release a scent when crushed. From late spring into early summer the stems end in dense, erect spike-like racemes 3-6 inches (8-15 cm) long. Each small flower has a single dark purple petal with protruding orange anthers, unlike most legumes, which carry five petals. Curved seed pods 0.25-0.35 inch (6-9 mm) long follow, each dotted with glands and holding one or two seeds. The species grows along stream banks, floodplains, and disturbed ground, tolerating both periodic flooding and summer drought once established. It spreads by seed and root suckers and can form thickets, which limits its use in small or formal plantings. The roots host nitrogen-fixing bacteria. Outside its native range it has naturalized and is listed as invasive in parts of Europe and Asia.
Native Range
Amorpha fruticosa is native to much of central and eastern North America, from southern Canada through the United States to northern Mexico, where it grows along rivers, streams, and wetland margins.Suggested Uses
Used in naturalized plantings, rain gardens, stream-bank stabilization, and erosion control on slopes and floodplains. The suckering habit suits large informal areas rather than confined borders. It is also grown in pollinator and native plant gardens within its range.How to Identify
Appearance
Size & Dimensions
Height6' - 12'
Width/Spread6' - 10'
Bloom Information
Flowering occurs from late spring into early summer, generally May to June across most of the range. The dense terminal racemes open from the base upward over two to three weeks. Bees and other insects visit the flowers, and the orange anthers shed pollen against the dark purple petals.
Detailed Descriptions
Flower Description
dark purple with orange anthersFoliage Description
medium greenGrowing Conditions
Sun Requirements
Requires 4-8 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Amorpha fruticosa grows in full sun to partial shade and adapts to a wide range of soils, including clay, loam, and sand, at a pH of 6.0-7.5. It tolerates both wet sites such as stream banks and dry spells once the deep root system establishes. Water is needed through the first season; established plants rarely require irrigation. The roots fix nitrogen, so supplemental fertilizer is seldom necessary. Plants spread by seed and root suckers and can form thickets, so open settings or periodic sucker removal keep it within bounds. Hardy in USDA zones 4-9, it tolerates winter cold to about -30F (-34C).Pruning
Pruning is done in late winter to early spring before new growth. Plants tolerate hard cutting back, which controls the open, leggy habit and stimulates dense regrowth. Removing root suckers during the growing season limits spread into surrounding beds.Pruning Schedule
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winterearly spring