HARDINESS: Zones 4 to 9
PREFERRED SOIL pH: Acid to neutral
PREFERRED SOIL TYPE: Moist, loamy
PREFERRED LIGHT: Sun to partial shade
ATTRIBUTES: Fragrant flowers in white or pink; for beds, edgings, specimens
SEASON OF INTEREST: Summer
FAVORITES: 'Ruby Spice', 'Rosea', 'Pink Spires', 'Hummingbird', 'Paniculata'
QUIRKS: Thrives in soggy soils
GOOD NEIGHBORS: Azalea, serviceberry, hydrangea, Japanese anemone, spring bulbs
WHERE IT GROWS BEST: Moist woodland settings
POTENTIAL PROBLEMS: Beetles, red spider mites
PRUNING: Clip off old seed heads in early spring
CRITTER RESISTANCE: Good
SOURCE: Nursery plants
DIMENSIONS: 3-8 ft (1-2.4 m) tall and 4-6 ft (1.2-1.8 m) wide
Clethra in the Landscape
Commonly known as summersweet or sweet pepperbush, clethra is an essential shrub for gardeners who crave fragrance. The 4 in (10.2 cm) long bottlebrush-shaped flower spikes appear in mid to late summer and last into fall, filling the air with their spicy-sweet perfume and attracting bees and butterflies. Not only are the blossoms welcome at a time when little else is in bloom, but the foliage is lovely all season. Ribbed and lighdy toothed, the oval green leaves are downy when young and turn a clear yellow in autumn.
Clethra is native to the eastern woodlands of North America, where it usually grows as an understory tree. When given good garden soil and at least a half day of sun, it grows into a robust, naturally rounded bush up to 8 ft (2.4 m) tall. Clethra's growth habit is also affected by soil moisture. An ideal shrub for damp locations, clethra transforms an abundant water supply into numerous leafy stems. In drier sites, it is more likely to grow tall with a lean profile.
Grow it along a woodland edge with other shade-tolerant plants, such as serviceberry, hydrangea, or dog-
wood. Or use it as a specimen plant at the back of a border that receives partial shade, mixing it with such companions as Japanese anemone, cohosh, perennial geranium, and ornamental grasses. Clethra also makes a fine freestanding shrub when used to define the edges of a lawn, and smaller cultivars can mark an informal path. The shrubs withstand salt spray, so are useful for seashore sites, and tolerate the shade of buildings when planted around foundations. And because it leafs out late in spring, clethra is a good shrub to underplant with any number of spring-flowering bulbs.
Clethra is undergoing a revival of interest because many new forms are available in an array of sizes and colors. Check plant tags carefully, because new cultivars vary in their mature size. If you want a large shrub, look for either the species, which bears white flowers that may be pinkish in bud, or the 6 ft (1.8 m) tall 'Ruby Spice', which has dark pink flowers. 'Rosea' and 'Pink Spires' are smaller varieties, seldom growing more than 4 ft (1.2 m) tall, with soft pink flowers. 'Paniculata' has slightly arching branches and larger flowers than the species. For tight spots, look for the petite, white-flowered 'Hummingbird', which grows only 3 ft (1 m) tall and wide but has the same sweet fragrance of other clethras.
One of die most attractive attributes of clethra is that it takes care of itself. Set out plants as promptly as possible in early spring to give them time to establish before summer. They like soil with a pH of 4.S-7.0. If you have alkaline soil, add garden sulfur per package label to adjust the pH. Keep the soil constantly moist for the first 2 months after planting by watering regularly and maintaining a 2 in (5.1 cm) deep organic mulch. Although clethras prefer moist conditions, after they develop extensive roots they are surprisingly drought tolerant. They need little or no fertilizer.
Clethras can be left unpruned, although most gardeners prefer to remove old flower spikes in winter or early spring, before new growth begins. If clethras outgrow their welcome, they respond well to pruning at almost any time of year. In Zones 4 to 6, mulch over the root zone, applying a 6 in (15.2 cm) thick layer of fluffy evergreen boughs, dried leaves, or straw after the ground freezes to protect the shallow roots from damage.
Although problems are rare, many of the insects attracted by clethra's fragrant blossoms also sample the leaves. Small holes in leaves are usually the work of night-flying beetles that do not cause serious injury. In dry, hot weather, sap-sucking red spider mites may cling to leaf undersides, causing leaves to look bleached. Knock them off with water from a hose and keep the soil moist to repel them. If Clethra attracts deer, tuck deodorant bar soap among shrubs or apply a commercial repellent as directed.