Diervilla: Flowering shrub with form and function

On Tuesday, I gave a lecture, “Gardening with Insects: The Little Things That Run the World,” to a group of earnest gardeners. Many of those in attendance had heard me speak last year on the topic of eliminating invasive plants from the landscape. As I renewed acquaintances with those who had attended this earlier talk, I learned of Norway maples that had been cut down, of more than one burning bush that had been dug up.

It was extremely gratifying to learn that my advice had been taken to heart. I left this group feeling energized in my efforts to help gardeners find native plant substitutes for invasive species. This sense of purpose was sustained when I returned to Marjorie’s garden to find dozens of bumblebees dancing among the bright yellow flowers of Diervilla lonicera, the native dwarf bush honeysuckle.

We planted these shrubs four years ago to prevent erosion on a steep slope bordering steps leading up from driveway to house. The best plants for this function have colonizing growth habits, spreading by underground stems to form broad thickets. We considered several species before deciding on the Diervilla. Few other native shrubs are as ornamental, stress-tolerant and ecologically functional.

Diervilla is a beautiful flowering native shrub with a most unfortunate common name. It is not a honeysuckle and in no way is it related to the highly invasive non-native shrub honeysuckles (Lonicera morrowii and L. tatarica) that were introduced for soil stabilization along roadsides and subsequently found their way into home landscapes. Because the seed is bird-dispersed, we now find extensive colonies of shrub honeysuckle in wooded natural areas where they have replaced the diversity of native trees and shrubs. I shudder to think of the possibility of someone seeking Diervilla lonicera for their garden but ending up with non-native invasive shrub honeysuckles, so make sure the nursery you are dealing with knows what you want. Use the scientific name, not the common name!

A deciduous shrub growing from 4 to 6 feet tall, Diervilla has an upright arching and spreading habit. The new leaves, light green with a touch of auburn, emerge in mid-May, gradually turning darker green as the weather warms. If the season stays cool and wet, the newest summer leaves continue to display the unique color mix of spring leaves. In autumn, the leaves turn first to yellow, then orange, and finally red. Diervilla is one of our loveliest fall shrubs.

Diervilla blooms throughout July with funnel-shaped blossoms, about a half-inch in length, that are clustered in the leaf axils. Pale yellow at first, the flowers slowly turn to orange or purplish red as they mature. They provide a steady income for native pollinators, particularly bumblebees, during a time of the year when few other plants are flowering.

Thriving in either sun or shade, Diervilla is extremely drought-tolerant and can be used in soils ranging from coarse sands to heavy clays. It is not tolerant of flooding, however, so do not plant it in low areas where snowmelt and early spring rain create seasonal ponds.

We purchased our Diervilla plants in 1-gallon containers, well-established plants that had already developed rhizomes. We planted them three to four feet apart on both sides of the steps. After a single growing season, shoots from the underground stems had emerged to fill in the spaces between plants. Now, four years later, we have what we envisioned, a continuous thicket of foliage and flower that not only holds the soil together but also provides ornamental beauty from May to November. Even the plant next to the driveway that gets whacked by the snowplow every winter is still thriving.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@ptc-me.net. Include name, address and telephone number.