Clethra alnifolia

Clethra alnifolia

  • By Pat Chadwick
  • /
  • June 2015 - Vol. 1 No. 6

Go native! Try Clethra alnifolia. We all appreciate plants that provide both beauty (form) and utility (function) in the landscape design. Clethra alnifolia is one such plant that provides both. Its graceful form, dark green foliage, fragrance, and generous floral displays keep the ornamental garden looking fresh and inviting in the summer months. As a native species, it functions as an excellent source of nectar and seeds for a variety of wildlife.

The name Clethra translates from the Greek word for Alder, which is a type of tree. Alnifolia translates as “Alder-foliaged,” because the leaves bear a faint resemblance to the leaves of the genus Alnus. Clethra goes by several common names, including sweet pepperbush, hummingbird plant, coastal sweet pepperbush, white alder, summersweet Clethra, or just simply summersweet. I prefer the last option — summersweet. Is that a great name for a plant or what? Just as its name suggests, it blooms in summer and it has a spicy, sweet fragrance.

Clethra alnifolia

Clethra alnifolia

DESCRIPTION

Form – Summersweet is a small to medium size, deciduous, suckering or colony-forming upright shrub. Depending on the cultivar, it typically ranges in size from three-to-eight feet tall.

Function – This shrub is useful as a single specimen in the ornamental garden. It is equally as attractive when planted as a grouping, a hedge, a foundation planting or as part of a naturalized landscape. This native species can be found in every state on the east coast from Maine to Florida and as far southwest as Texas. It provides nectar for hummingbirds, bees and butterflies in the summer and seeds for birds in the winter. As an aside, the C. alnifolia species may provide more nectar for pollinators than the cultivars. Deer and other four-footed pests appear not to have any interest in this plant.

Foliage – Although late to leaf out in spring, the medium textured, dark green foliage is very attractive. The serrated leaves are twotothree inches long, elongated to ovate in shape, and arranged in an alternating pattern along the branches. In autumn, the foliage turns golden yellow.

Flowers – The showy, fragrant flowers bloom on current year’s growth and are arranged in bottlebrush-like racemes at the tips of branches.   The blossoms on the C. alnifolia species are white. However, a couple of cultivars have attractive pink blossoms. After the shrub finishes flowering, it develops delicate, one-eighth inch, non-showy seed pods, which resemble peppercorns. As you might guess, this is the plant characteristic that prompted the name “sweet pepperbush.”

CARE AND MAINTENANCE

Although slow growing, summersweet is easy to grow in average or wet soils that are consistently moist and acidic. Despite its preference for moist soils, this versatile plant is fairly drought tolerant once it is established in the landscape. While it prefers full shade, it will tolerate everything from full sun to full shade. You can’t get any more flexible than that. I’ve had good luck growing it in full sun in the morning and shade in the afternoon. A generous layer of mulch over the root zone helps keep the soil cool and moist.

Good soil preparation is key to making this shrub happy. Dig a hole that is threetofour times as wide as the root ball, but only as deep as the root ball. Spread out the roots in the hole, fill in the soil over the roots, and water in well. Cover with twotofour inches of mulch to retain a steady moisture level while the plant is getting established.

Other than an occasional pruning, this shrub requires little in the way of maintenance. Prune in late winter or early spring before flower buds form. Cut out any damaged or dead branches at ground level.   If you’re not sure whether a branch is dead, try clipping off the tip. If you see white wood inside, the branch is still alive. To control the overall size of the shrub, prune about one-third of the longest stems back to the ground but do so randomly so that the shrub retains a natural look.

Summersweet can be easily propagated from stem cuttings in early summer or from seed that is planted in either spring or fall. If you are propagating from stem cuttings, take three-to-four inch long stem cuttings in the cool of the day from well-watered plants. Cuttings rooted in early summer have a better propagation success rate than cuttings started later in the summer. For those of us who like a challenge, harvest the ripe, brown seed capsules of the species and plant in the fall or spring.

Summersweet spreads by root suckering, but because it spreads slowly, it can be easily managed. Just remove the suckers with clippers or loppers.

Pests rarely bother this plant. Occasionally, they may suffer an infestation of spider mites. However, if the plant is kept well hydrated, spider mites tend to leave it alone.

CULTIVARS AND OTHER CLETHRA SPECIES

In addition to the native species, a number of C. alnifolia cultivars may be found at garden centers, including:

  • Hummingbird’ – A dwarf cultivar that tops out at about three feet and is wider than it is tall. The white blossoms are larger than the native species, open earlier, and appear in racemes that average fourtosix inches in length. This is a good choice for a small wildlife garden.
  • Sixteen Candles’ – A dwarf selection similar in size to ‘Hummingbird’ but with white flowers that are held more upright than “Hummingbird.’ It is also ideal for a small garden.
  • Pink Spires’ – A pink-flowering cultivar with flowers that are as fragrant as the white form. This cultivar can grow sixtoeight feet tall. One of the largest cultivars, this shrub can be used to fill a large space.
  • Ruby Spice’ – A sport of ‘Pink Spires,’ this cultivar has beautiful, deep rosy pink buds that open up to paler rose-pink blossoms in four-inch long racemes. On average, ‘Ruby Spice’ grows fourtosix feet tall and wide. The shape is generally oval but may be round.
  • Vanilla Spice™’ – An upright to rounded form with large white flowers that are approximately twice the size of the native species. This cultivar grows fourtosix feet tall and threetofive feet wide.

In addition to C. alnifolia and its cultivars, you may possibly encounter two other native species of Clethra in garden centers: C. tomentosa and C. acuminate.

  • C. tomentosa (also referred to as C. alnifolia var. tomentosa or downy sweet-pepperbush) is similar in appearance to summersweet. It is more heat tolerant than C. alnifolia and has hairier leaves and twigs. Two cultivars of tomentosa are ‘Cottondale,’ which has very long flower stalks, and ‘Woodlander’s Sarah,’ which has white-spotted leaves.
  • C. acuminata, also known as mountain sweet-pepperbush or cinnamon Clethra, is not currently easy to find in garden centers. In the wild, it can be found in rich, moist woods or in dry, rocky outcrops throughout the southern Appalachian Mountains, where it prefers the cooler areas of zones 6 and 7. According to horticulturist and author Michael Dirr, this shrub would be a good choice for a semi-shaded garden nook. Taller than C. alnifolia, it can reach 10 to 15 feet in height and is a very attractive plant.

Several other species of Clethra exist in other parts of the world, but they are generally not grown in this country.

RESOURCES

American Horticultural Society, A-Z Encyclopedia of Garden Plants, 2004.

American Horticultural Society, Plant Propagation, 1999.

Dirr, Michael A., Dirr’s Hardy Trees and Shrubs, 1997.

Millichamp, Larry, Native Plants of the Southeast, 2014.

United States Department of Agriculture Plants Database, http://plants.usda.gov.

Virginia Cooperative Extension Publication 450-236, Problem-Free Shrubs for Virginia Landscapes, (http://pubs.ext.vt.edu).

Virginia Department of Conservation and Recreation Native Plants Database, http://www.dcr.virginia.gov.