Diervilla lonicera a native groundcover option

Since my recent column about the invasive threat of non-native rugosa roses, I have received several comments and questions, all of them positive in the sense that these gardeners are willing to replace their rugosa roses but need a suitable alternative. For example, at a recent workshop on ecological landscaping, a participant asked me to suggest native shrub species to replace rugosa roses on a steep bank.

The issue was erosion control, holding the soil in place on a steep slope. The best plants for this function have colonizing growth habits, spreading by underground stems (rhizomes) to form broad thickets. Several species came immediately to mind, including meadowsweet (Spiraea alba var. latifolia) and sweetfern (Comptonia peregrina), but then I recalled what we planted last year in Marjorie’s garden to border the steep steps leading from the driveway to the house: dwarf bush honeysuckle (Diervilla lonicera). 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. Make sure the nursery you are dealing with knows what you want. Use the scientific name, not the common name!

A small deciduous shrub growing to only three or four feet tall, Diervilla has an upright arching and spreading habit. The new light green leaves emerge in mid-May, gradually turning to a dark green as the weather warms. If it stays cool and wet, as it has this year, the newest summer leaves display a unique pattern of light green and auburn. 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 bells, about a half-inch in length, that are clustered in the leaf axils. Pale yellow at first, they 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 course sands to heavy clays. It is not tolerant of flooding, however, so do not plant it in low areas where snow melt and early spring rain create seasonal ponds. We purchased our Diervilla plants in one-gallon containers, well-established plants that had already developed rhizomes. We planted them three to four feet apart on both sides of the steps and, after a single growing season, shoots from the underground stems have emerged to fill in the spaces between plants. Even the plant by the driveway that got whacked by the snow plow is recovering. I suspect that by this time next year we will have what we envisioned, a continuous thicket of foliage and flower that not only holds the soil together but provides ornamental beauty from May to November.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to reesermanley@shead.org. Include name, address and telephone number.