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Native plants are becoming increasingly popular as gardeners seek specimens of high ecological value to support declining pollinator populations of insects. Among the nearly 2,300 species of plants known to be native to Illinois, our native shrubs are often overlooked and underestimated in the landscape. However, many offer a variety of ornamental attributes along with a high pollinator value.

Indigo bush (Amorpha fruticosa), also known as false indigo, is a native shrub typically found in habitats associated with rivers. It visits river banks and other lowland sites with more open tree canopies and partial sun, as well as forest edges and prairie habitats found near streams. Like many other plants found along streams, it is adapted to a wide range of conditions and will tolerate very wet soils, including occasional flooding.

This adaptability to moist soil results in excellent tolerance to urban soil conditions, which are often compacted and of lower quality than naturally occurring soils. Because the indigo bush easily tolerates the low oxygen levels associated with flooded soils, it adapts well to compacted soils that are also low in oxygen. As an added bonus, this plant is a nitrogen fixer, meaning it can release nitrogen into the soil through a symbiotic relationship with soil bacteria.

The flowers of this plant are exceptional, filling the shrub crown with purple to indigo spikes that can grow to 6 inches long. The contrasting yellow anthers, the pollen-bearing parts of the flower, create a striking display for several weeks at this time of year.

The plants in my garden are almost done flowering for the season and have been a flurry of pollinator activity for the past few weeks. As each flower structure develops at the branch tips, sometimes in clusters of up to four individual spikes, new flowers slowly mature to produce a steady supply of nectar and pollen for up to about three weeks. I always enjoy watching the contrasting purple and yellow color move from the base of each flower structure to the tips during its flowering period.

The foliage of this plant is an attractive light green and consists of finely textured compound leaves with tiny leaflets about 2.5cm long. It casts a diffused shadow, similar to the honey locust, that lets in plenty of light for smaller plants to thrive underneath.

Indigo bush matures into a large, spreading shrub that sometimes reaches up to 15 feet in full sun. It also forms thickets as it spreads through new shoots, which limits its application as a specimen plant. In the right place with space to spread out, however, a wonderful natural privacy screen or hedge planting is created. Size and spread can be limited by selective pruning or rejuvenation pruning (removing all stems at ground level). This plant flowers on new wood, so pruning should be done in late winter or early spring before bud burst.

For a smaller version of this plant with comparably attractive, finely textured foliage and very similar purple-yellow flowers, consider adding Lead Plant (Amorpha canescens) to your landscape. It matures into a rounded shrub about 4 to 5 feet tall and slightly wider than it is tall. Leadplant flowers a little later in the year but offers an equally long flowering time of around three weeks and plenty of appeal to pollinators.

I actually had lead plant in mind when I bought the indigo bush that now sits happily in our front yard. I read “Amorpha” on the plant label, but the species was not registered as my memory of that distinction must be a bit blurry. Both plants have several common names, so I’m sure I missed that detail. Nonetheless, I was thrilled to see my “lead plant” grow profusely in its first season, thinking I must have placed this plant perfectly, and praising myself for such great gardening skills.

The plant is now in its third year of growth and is literally shooting out of the planting site. This year, her impressive size and earlier than expected flowering called my species selection into question. As I went back to check the plant label and brush up on my latin, I realized that this shrub was certainly a case of mistaken identity. I had actually planted A. fruticosa, thinking it was A. canescens.

As gardeners, we all like to experiment, so I’ll attribute this mistake to experimentation. I look forward to seeing if my plant can peacefully coexist with others in its limited space. A rejuvenation pruning is definitely on the agenda for next spring!

Ryan Pankau is a Horticultural Educator with UI Extension serving Champaign, Ford, Iroquois, and Vermilion counties. This column also appears on his Garden Scoop blog at go.illinois.edu/gardenscoopblog.

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