By: Julie Jenkins
Greenhouse Manager at Ion Exchange, Inc.
AMORPHA FRUTICOSA is also known as False Indigo, Indigo Bush, Desert False Indigo, or River Locust. This is a native perennial shrub that will grow 4-16 feet tall with occasional branching. The lower stem becomes woody and smoothly gray while the upper stem is dull light green. The ½-1 ½ foot leaves are alternate on relatively short petioles with 11-35 leaflets that are each 1-2 inches long, ½-1 inch wide, and are dull gray green. The leaflets are paired along the central stem with a single leaflet attached at the stem tip so the total number of leaflets is always uneven. The undersides of the leaflets have visible glands that appear as scattered small dots. Unlike the related Amorpha canescens, False Indigo is hairless and much larger in all aspects.
In June, July, and August 3-8 inch spike-like flower clusters develop from the upper branches. This species is a valued ornamental because of the showy blooms. The individual flowers are a ¼ inch long tubular structure from a single purple petal which is wrapped around ten yellow stamens. Amorpha is from the Greek term describing “without shape” in reference to the single petal design of the flower. Seed pods of about ¼ inch long replace the flowers and each pod contains 1-2 seeds. For optimal germination the seed hulls should be removed. Moist, cold stratification for 10 days will also enhance germination.
False Indigo is found growing in wet thickets and along stream and river banks and prefers full to partial sun but does not survive well in shade. This species tolerates a variety of soils and is capable of withstanding occasional flooding. It is valuable as a soil anchor along stream banks. Since it is a legume it fixes nitrogen in the soil. Small to medium sized bees looking for nectar and pollen typically pollinate the flowers. The purple blossoms also provide nectar for butterflies. Caterpillars of various butterflies and moths feed on the foliage and flowers. False Indigo provides good wildlife food. Bobwhite quail eat the fruit and deer will occasionally browse on this shrub. Despite the open growth of the False Indigo, Red winged blackbirds frequently make use of it as a nesting site.
Amorpha fruticosa is native to much of the continental United States but is considered an invasive species in some locations. It is not considered native in the Pacific North West but has distributed itself along rivers and streams where it is not really welcome.
The roots and stems of the False Indigo contain rotenone which is used as an insecticide and fish poison. Some commercial use yields a poor indigo (blue) dye.
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