clethra alnifolia ruby spice

How To Grow and Care for Summersweet (Clethra alnifolia)

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There aren’t too many fragrant showy native plants that will bloom in a shady position in late summer. The Summersweet, however, does just that and if you live in zones 3 through 9, this is definitely a plant that you should consider for your garden. 

What Is A Summersweet Plant? 

The summersweet, which is also known as the summersweet clethra, sweet pepper, coastal pepperbush, coastal sweet pepperbush, alderleaf clethra, or alderleaf pepperbush is an upright deciduous shrub of the Clethraceae family.

Summersweet plants usually grow 4-9ft (1.2-2.7m) tall and about 6ft (1.8m) wide, although they may spread into a mounded clump if allowed to sucker. These shrubs are native to the eastern regions of the United States, where they can be found in woods and thickets, often in swampy areas and along streams. 

The alternately arranged leaves are glossy green and have serrated margins. These leaves typically grow to a little over 2 inches (5cm) in length and tend to regrow quite late in spring. In the fall, the leaves turn an attractive golden-yellow shade and persist for up to a month before being shed. The bark of these plants is quite attractive and varies between shades of gray to orange or red.   

summersweet
Summersweet – Sweet Pepperbush photo by John Brandauer | Flickr (CC BY-NC-ND 2.0)

Summersweet Flowers

The summersweet produces a 3-6 inch (7.5-15cm) long raceme, consisting of very small flowers that may number in the dozens on a single flowerhead. Wild forms of these flowers are white in color, while pink cultivars are now available. 

The blossoms have a strong, sweet, and spicy fragrance when they bloom in mid to late summer. The flowers of this plant last for up to 6 weeks and then mature into dark brown fruits that persist well into the winter and provide some cold season interest.

Cultivars

While the wild-type of the clethra alnifolia plant has quite an upright growth form and white flowers, several cultivars are now available with varying shapes and flower colors. 

  • ‘Hummingbird’ is a very showy and compact, white-flowered form that reaches about 4ft (1.2m) tall and 5ft (1.5m) across.
  • ‘Pinkspire’ and ‘Ruby Spice’ are beautiful pink-flowered forms. ‘Ruby Spice’ has darker pink flowers and both forms reach a height of around 6ft (1.8m).
  • ‘September beauty’ is a white-flowered variety that flowers about a month later than other varieties, providing late-season brightness to the garden. 
clethra alnifolia ruby spice
Clethra alnifolia ‘Ruby Spice’ (Summersweet) Photo by F.D.Richards | Flickr (CC BY-SA 2.0)

How To Grow A Summersweet Shrub

These bushes can be successfully grown from seeds, however, the seed takes some time to mature and should be collected in mid-winter. These seeds should be surface-sown and will germinate in 2-4 weeks. (1) Summersweet is also very easy to grow from stem cuttings taken in the summer, or root cuttings taken in the winter.

The summersweet plant prefers a well-drained, acidic soil that should not be allowed to dry out. Although these plants can be somewhat drought tolerant once well established, they are adapted to grow in moist environments so keep that in mind when watering your clethra plant.

Summersweet bush is very adaptable to light conditions and can be grown in any position, although partial or dappled shade sites in USDA Hardiness Zones 3-9 are recommended. 

Care and Maintenance

Summersweet is a low-maintenance plant that spreads slowly by suckering but is easily managed by cutting off these suckers before they are allowed to develop. These plants are tolerant of pruning although they don’t necessarily need it. If you do wish to neaten up a plant or rejuvenate it, however, the recommended pruning time is late winter to early spring, since these plants bloom on new growth, and will grow out nicely to flower well.  

Summersweet plants are not heavy feeders but may benefit from a light application of fertilizer just after pruning. These plants are generally pest and disease resistant, although they are known to be susceptible to damage by spider mites in drier and hotter areas. 

Pseudocercospora leafspot can also affect these plants in years with late rainfall. Being a deciduous plant, this does not necessarily require treatment as the leaves will be shed. Practicing good hygiene, however, by being careful not to spread the infection to other plants in the garden and removing fallen leaves is a good practice. (2) 

Uses

Horticultural uses

Summersweet shrub can be grown as an attractive native border plant or low hedge. The plant has good salt tolerance so it’s a great option for coastal gardens that aren’t exposed to salt spray (1). This is a great option for late summer color. 

Human uses

These plants may be used for erosion control along streams and watercourses as well as planting below powerlines where they inhibit the growth of taller plants if left to spread by suckering. (3)

Wildlife uses

Sweet pepperbush flowers attract hummingbirds, bees, and butterflies, and the fruits of this plant are eaten by birds that spread the seeds. This plant is generally avoided by deer unless little else is available.

FAQs

Conclusion

While the summersweet plant may not be evergreen, they do provide a valuable splash of color to the garden landscape in positions and times of the year when other plants have already finished flowering. Their manageable size and sweet fragrance are added benefits.

For more shrubs to grow, check our list of flowering shrubs.

References

References

(1) Griffin, J. J. & Blazich F. A. The Woody Plant Seed Manual. 

(2) Williamson, J. Summersweet Clethra Fact Sheet. https://hgic.clemson.edu/factsheet/summersweet-clethra/

(3) Wennerberg, S. Coastal Sweet Pepperbush Clethra alnifolia Plant Guide. 

https://plants.usda.gov/plantguide/pdf/pg_clal3.pdf

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*photos used with permission from the owners.

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