The general habit of Indigo Bush. Plants will grow to 10' tall or more but can be pruned back. Photo: Paul Cox, Lady Bird Johnson Wildflower Center
False Indigo, Amorpha fruticosa
Do you happen to have a spot in your yard that stays pretty wet through the growing season? Have a creek or access to a riverbank from your property? False Indigo might be a good native to consider for the back of the garden.
We know Lead Plant (Amorpha canescens) as a nitrogen-fixing, low-statured (1-3’) native plant of full sun and dry soils. False Indigo, a related species, looks similar but is opposite in a number of ways.
First, False Indigo can grow fairly tall if it is in a place with sufficient moisture; up to 8 to 10 feet tall. Branching infrequently, at that height it can look somewhat ungainly but it takes to pruning for a bushier appearance. Like Lead Plant, the leaves are compound but larger and each leaflet has a clear stem.
Indigo Bush, as this species is also called, is a plant of wetter places. In the wild it is found on the edge of rivers and streams, and in wet-wet mesic prairies and sedge meadows. It also grows in open bottomland woodlands where there is still some light. As indicated by its natural habitats, it tolerates temporary flooding. It is not particular about soil type. Mine is planted at the base of my rain barrel near my overflow at the southwest corner of the house and seems quite happy.
Small flowers, each with a single deep-purple petal wrapped around the reproductive structures, develop on a spikey raceme up to 8 inches long at the branch ends and bloom for 2-3 weeks sometime in late spring or early summer. Somehow it reminds me of Butterfly Bush, perhaps because of the butterflies I have seen nectaring on the flower spikes.
Indigo Bush attracts a wide variety of small to medium-sized bees, one of which, Andrena quintilis, is a specialist pollinator of this genus. It is also a host plant for the Silver-spotted Skipper, the Dogface Sulfur butterfly and the Common Tan Wave moth, and is a food source for a number of other plant bugs and beetles. Deer will browse occasionally but small colonies will form if conditions are favorable.
While Indigo Bush can get tall and require pruning every several years, it is worthy of being considered for the garden because of its support for a wide range of pollinators. Incidence of this species is decreasing in the wild.