It is often said that our strongest memories are evoked through our sense of smell. For many, the delightful scent of our native summersweet, Clethra alnifolia, calls to mind summer on the Vineyard. At the peak of the season, summersweet’s scented white flowers perfume the air with their sweet fragrance. Adapted to flowering in deep shade as well as in full sun (with sufficient moisture), large colonies of this native shrub occur in natural areas throughout the Island.

The small white flowers form dense two to six-inch-long spikes on the tip of each branch appearing in concert with our summer crowds in July and August. After flowering, summersweet forms attractive brown seed capsules resembling peppercorns that persist throughout the winter months. This distinctive feature in combination with its sugary scent has earned the plant another common name: sweet pepperbush.

With an extensive North American natural range from Maine to Florida to coastal Texas, this multi-stemmed shrub typically grows from four to eight feet tall with an equal or greater spread. Summersweet has a tendency to sucker. On many Martha’s Vineyard Land Bank properties and along municipal roadsides near wet woods, shrubs are often mowed to the ground for safety or sight-line improvements. Summersweet responds by increasing the production of underground stems to colonize a large area. Where this occurs, one single plant may occupy an area of 100 square feet or more.

A satisfying landscape and garden plant, summersweet can be used for a foundation planting or for naturalizing in a large mass. Its late summer flowers light up shady areas. In late fall its bright yellow foliage provides even more enjoyment. Plants are generally trouble-free, but avoid planting in dry, sandy soils with full sun exposure. The shrubs will become water-stressed and susceptible to red spider mites that can attack the foliage and weaken the plant.

Summersweet is often found in our moist woodlands as an understory to red maple and beetlebung (Nyssa sylvatica), or pondside in the company of high bush blueberry and the swamp azalea (Rhododendron viscosum). Look for it in wet zones at pond edges. It flourishes at Priester’s and Mill Ponds in West Tisbury and dominates swampy areas along Middle Road and Tea Lane in Chilmark. Clethra alnifolia thrives in acidic soils and tolerates brackish water; as a result, it can be found in a wide range of Island natural areas.

Propagating summersweet is easy. Seed collected in the late fall can be stored dry in a tupperware container in a common refrigerator. Sow the seed in early April on a sunny windowsill. Seed sprouts readily. You can also grow it easily from summer cuttings. Collect stem cuttings just after flowering. The top stems can be cut into four inch lengths and placed in a 4 inch plastic pot covered with Saran or plastic. With patience and a green thumb, like Polly Hill, you can grow your own!

 

Tim Boland is executive director at the Polly Hill Arboretum. This column appears every Tuesday.