Clethra: The Sweetest Summer Shrubs

I distinctly remember my first encounter with Clethra alnifolia (Summersweet or Sweetpepperbush). The air was thick with its spicy sweet fragrance and it begged me to search for it source. Tucked into the center of a large shrub boarder was a tall, gangly plant with small white spires about eight feet in the air. Not much of a plant, but it was obvious that it had never been pruned or cared for. Despite its poor habit, I felt that any plant that smelled that sweet deserved to be used. Some years later I specified Clethra in a landscape design. Of course I was a naïve greenhorn, too foolish to realize that it was not available in the trade for purchase. But I was smart enough to realize it was a plant worth growing.

Times have changed and so have our pallet of plants. Today Clethra is available to purchase at nearly every landscape pick-up yard, so are a host of improved cultivars. How is it that within a period of 25 years, so much can change?

It all started with Clethra ‘Hummingbird,’ the first dwarf form of Sweetspire. It was an obscure plant that Fred Galle of Callowway Gardens had discovered and for the most part had been forgotten. Then Richard Feist, a Callowway intern at the time, saw the plant and bells went off. With the permission of Galle he registered the plant as ‘Hummingbird’ and then wrote an article in Field Notes in American Nurseryman. All of a sudden Clethra was worthy. Clones started coming out of the woodwork; ‘Rosea’, ‘Pink Spires’, ‘Creal’s Callico’, ‘Fern Valley Pink’, ‘Hokey Pink’, ‘Cottondale’, ‘September Beauty’, ‘Ruby Spice’, ‘Sweet Suzanne’, ‘Sixteen Candles’, ‘White Dove’ and ‘Sherry Sue’ just to name a few.

While Clethra is relatively easy to fine these days, it is still greatly under used. In my travels to Europe, I am amazed that the plant has gained little respect; it is available only at collector type nurseries. How can it be?

Summersweet is an American native that can be found along the Eastern seaboard from Maine to Florida and west into Texas; along its western range it is native as far north as Tennessee. As a facultative wetland species is most likely to be found growing in low, moist woodlands, especially in the South, but in its northern range it is not unlikely to find the plant on higher, drier ground. You need not plant this shrub in a swamp to have success. My garden is nearly pure sand, and with the regular irrigation the plant grows just fine. Just remember that Clethra is not a plant for droughty soils. USDA zones 5-9.

Plant height varies greatly depending upon the cultivar. While the species can reach eight feet in height, cultivars such as ‘Hummingbird’, ‘Sixteen Candles’ and White Dove™ max out around three feet. Regardless of cultivar Summersweet benefits from pruning especially at a young age. Regular pruning creates a bushier, fuller plant as opposed to a leggy bare bottomed plant. Clethra alnifolia, especially the variety tomentosa can be suckering or stoloniferous. My observation has been that suckering is more prevalent in moist soils, while it is almost nonexistent on drier soils. Even where suckering is prevalent, it is never so aggressive that it presents a problem.

Flowers while typically white, can also be pink (‘Pink Spires’, ‘Hokey Pink’, ‘Rosea’) or near-red, dark pink such as ‘Ruby Spice’. The light pink varieties are quite attractive and should not be abandoned totally in favor of the darker ‘Ruby Spice’; even though the flowers may fade to near white as they age it is still a pleasing pink in the garden. The blooms appear in late summer; in Michigan we begin to see flowers in late July with August being prime bloom time. The cultivar September beauty™ extends the flowering season several week later than the other cultivars. Leave color ranges from a grey-green (‘Cottendale’) to dark green (Hummingbird, September Beauty, Sixteen Candles and White Dove™) with most other cultivars falling somewhere in between.

A check list of Cultivars:

‘Anne Bidwell’ - Panicle inflorescence with multiple racemes. Selected by Anne Bidwell.

‘Cottondale’ (var. tomentosa) - A selection with very large racemes up to 16” in length and grey-green leaves, suckering. Selected by Woodlanders Nusery.

‘Compacta’ - A very attractive selection with compact branching and a rounded habit of about 4’ in height. Selected by Tom Dilatush.

‘Creels Calico’ - A suckering plant with highly variable variegation. More of a curiosity than a landscape plant. Selected by Michael Creel.

'Fern Valley Pink' - Long, light pink flowers. Selected by Tom Clark.

‘Hokie Pink’ - Light pink flowers, more compact than typical. Selected by Jime Monroe.

‘Hummingbird’ - A low, compact, mounded plant maturing around 3’. Very dark green foliage and good yellow fall color. Selected by Fred Galle.

‘Pink Spires’ - Light pink flowers, matures at 6’-8’.

‘Rosea’ - Very similar to Pink Spires

‘Ruby Spice’ - A sport mutation of 'Pink Spires' with red flower buds that open to a rich pink. Does not fade to white. Very good yellow fall color. Selected by Andy Brand.

‘Sherry Sue’ - Typical white flowers, young stems are an attractive cherry red. Brought to us from the J.C. Raulston Arboretum.

‘Sixteen Candles’ -A seedling of Hummingbird with tight growth and larger white flowers. A fine plant selected by Mike Dirr.

‘Sweet Suzanne’ - Another seedling of Hummingbird with large flowers. Has been a weak grower for us, not as good as above. Selected by Mike Dirr.

var. tomentosa -A suckering plant with grey green leaves. ‘Cottondale’ is a superior selection

White Dove™ - Another seedling of Humingbird, Compact habit and larger white flowers. Selected by Flowerwood Nursery.


Related Species:

Clethra acuminata: Cinnamon Pepperbush - A small tree or larges suckering shrub at 12-15' in height. White flowers borne in termial racemes, with only slight fragrance. Attractive cinnamon colored bark. USDA Zones 6-8.

Clethra barbinervis: Japanese Pepperbush - A small tree or large shrub 15'-20' in height. White, fragrant flowers in terminal panicles in mid-summer. Superb exfoliating bark. An excellent plant for USDA Zones 6-7.