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.
| Common name | Alderleaf Clethra, Alderleaf Pepperbush, Clethra, Coastal Sweet-pepperbush, Summersweet, Sweet Pepperbush |
| Botanical name | Clethra alnifolia |
| Family | Clethraceae |
| Species | alnifolia |
| Origin | Eastern North America |
| Life cycle | Perennial |
| Plant type | Native Plant |
| Hardiness zone | 3, 4, 5, 6, 7, 8, 9 |
| Sunlight | Full Sun |
| Maintenance | Low |
| Soil condition | Clay |
| Soil ph | Acid |
| Drainage | Well-Drained |
| Growth rate | Medium |
| Harvest time | Fall |
| Flowering period | Summer |
| Height | 5 ft. – 10 ft. |
| Width | 5 ft. – 10 ft. |
| Flower color | Pink |
| Leaf color | Green |
| Fruit color | Brown, Copper |
| Stem color | Brown, Copper |
| Fruit type | Capsule |
| Leaf benefit | Showy |
| Flower benefit | Fragrant |
| Garden style | Children’s Garden |
| Uses | Coastal |
I. Appearance and Characteristics
Clethra alnifolia, the coastal sweetpepperbush or summer sweet, is a species of flowering plant in the genus Clethra of the family Clethraceae, native to eastern North America from southern Nova Scotia and Maine south to northern Florida, and west to eastern Texas. It is a deciduous shrub which grows in wetlands, bogs and woodland streams.
The Latin specific epithet alnifolia means “with leaves like alder (Alnus)”. This gave rise to another common name, common white alder, though the two plants are not closely related.
Growing to 1.5–3 m (4 ft 11 in – 9 ft 10 in) tall, it is a deciduous shrub. The leaves are obovate to oblong, 4–10 cm long and 2–4 cm broad, with a serrated margin; they are green turning yellow-golden during the autumn. The flowers are white or very pale pink, 5–10 mm in diameter, and have a sweet, somewhat cloying fragrance. The flowers, which are attractive to bumblebees, are produced in racemes up to 15 cm long and 2 cm broad in late summer, depending on the cultivar. The scent of C. alnifolia is described as sweet. The “pepper” part of the common name derives from the mature fruits, capsules which have a vague resemblance to peppercorns, however with no element of spiciness.
It grows in wet forests, pine flatwoods, wetlands, bogs and can be seen alongside woodland streams. It prefers a neutral to acidic soil. The Nova Scotia population is small and endangered.
II. How to Grow and Care
Sunlight
Plant summersweet in an area that receives full sun to part shade. An area with morning sun and afternoon shade is ideal.
Temperature and Humidity
Summersweet thrives in moist climates, and tolerates both heat above 100 degrees Fahrenheit and freezing cold winters. It is originally from eastern and southern North America, but grows naturally along the Atlantic coast and west to Texas. Its natural environment includes wet and swampy areas of woodland as well as marshes and river banks.
Watering
Summersweet prefers moist soil and even grows well in areas with standing water.
Soil
This plant can work in a variety of soil pHs, types, and moisture levels. It prefers acidic, sandy soil that is moist but will tolerate clay soils, as long as they’re amended with organic material, and full shade. Water regularly as needed so the soil does not dry out.
Fertilizing
A one-time fertilization with a slow-release shrub and tree fertilizer in the early spring is enough, as summersweet is a light feeder. For the amount to use, consult product label instructions.
Planting Instructions
Plant summersweet in the spring. Dig a hole at least twice the size of the root ball and just as deep. Place the shrub in the hole and gently spread out the roots. Backfill with the original soil so that the top of the root ball is flush with the soil. Tamp down the soil and water it well. Keep the soil moist and water it regularly during the first growing season to encourage a strong root system.
Space plants 4 to 6 feet apart, depending on the intended landscape use. To grow it as a specimen, give it more space. For a hedge, plant the shrubs closer together.
Pruning
Other than removing damaged or dead branches, pruning of summersweet it optional and the shrub responds well to pruning. It blooms on new wood so you can prune it in the late winter or early spring without worrying about accidentally removing flower buds. The best time to prune is after it has started to leaf out.
Propagation
Softwood stem cuttings, taken in early summer, are the best way to propagate summersweet. Use clean garden shears to cut 3- to 4-inch cuttings, taken in the morning, from well-established healthy plants. Remove lower leaves on the cuttings, dip the ends in rooting hormone, and tuck into a mixture of half perlite and half potting soil. Keep in a high-humidity area, and cover with plastic. Once roots are established—at least five weeks, but likely longer—you can bring your cuttings outside to plant in your garden.
How to Grow from Seed
Summersweet seeds are easy to plant and they germinate quickly; seeds can be harvested in autumn and have no specific storage needs. They can be planted immediately, or the following spring. To do so: Fill seedling trays or pots with moist potting mixture, and press the seeds in so they are halfway-buried. Cover with a thin layer of sand, then keep them in low light under plastic. Water seedlings as needed, then plant when they’re sturdy. There’s no need for cold stratification to germinate.
Pests and Diseases
This shrub has no serious insect or disease problems. In dry conditions, it might attract spider mites. In wet fall weather, it might get infected with leaf spot but since this occurs late in the season and the shrub will drop its leaves shortly thereafter, it does not warrant treatment. Just make sure to rake and collect all diseased leaves.
Potting and Repotting
If you want to grow summersweet in a pot, select a dwarf variety such as Sugartina (‘Crystaltina’). Use a container that has large drainage holes and is big enough to accommodate two to three years of growth, about 8 inches wider than the root ball. Fill the container with a well-draining potting mix. Like all potted plants, it will need frequent watering, up to daily in hot summer weather.
Although summersweet is very winter-hardy, container-growing exposes the roots to the cold, which can cause dieback. If you live in a region with subzero winters. you need to winterize the pots, either by sinking the container in the ground, placing it in a second, larger pot to create a planting silo, or wrapping the pot in several layers of burlap or bubble wrap.
Overwintering
Use a 3-inch layer of organic mulch to protect your summersweet in the winter. Once spring comes, you can take it away.
III. Summersweet Varieties
- ‘Creels Calico’: the shrub features dark green leaves that are dark with splotches of creamy white
- ‘Crystalina’: with this plant, you get white flowers with the same spice fragrance with golden brown foliage in the fall.
- ‘Hummingbird’: the plant has a compact size with fragrant white flowers.
- ‘Pink Spires’: the plant forms clusters of pink blooms with foliage changing color.
- ‘Rosea’: the salmon-hued flower spikes are a standout on this plant, fading to pinkish-white
- ‘Sixteen Candles’ has long white spikes with many flowers and deep green foliage.
IV. Uses and Benefits
Summersweet is a rather uncommon shrub that blooms late in the summer season. It can be used as a hedge but also looks nice in a shrub border. Summersweet makes a great addition to naturalistic, woodland, or cottage-style gardens. Dogwood, asters, and purple coneflowers make a wonderful combo with this plant.
It’s also used as a naturalizing shrub. In addition, summersweet is great for attracting pollinators, like bees and hummingbirds, to the area.
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