Commonly known as summersweet or sweet pepperbush, clethra is an essential shrub for gardeners who crave fragrance. Check out this beginner’s guide to growing clethra and add it to your garden today!
A brief introduction to clethra
The 10-centimetre-long (four-inch-long), bottlebrush-shaped flower spikes appear in mid to late summer and last into fall, filling the air with their spicy-sweet perfume. Not only are the blossoms welcome at a time when little else is in bloom, but the foliage is lovely all season. Ribbed and lightly 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 2.4 metres (eight feet) 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 dogwood. 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 free-standing shrub when used to define the edges of a lawn.
- 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.
Expert tips for growing clethra
- One of the 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 4.5 to 7.0. If you have alkaline soil, add garden sulphur per package directions to adjust the pH. Keep the soil constantly moist for the first two months after planting by watering regularly and maintaining a five-centimetre-deep (two-inch-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. In Zones 5 and 6, mulch over the root zone, applying a 15-centimetre-thick (six-inch-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 do not cause serious injury.
- In dry, hot weather, sap-sucking spider mites may cause leaves to look bleached. Knock them off with water from a hose and keep the soil moist.
- If clethra attracts deer, tuck deodorant soap among shrubs or apply a commercial repellent as directed.
A fresh new array of clethra
Clethra is undergoing a revival of interest because many new forms are available in an array of sizes and colours. Before getting started, check plant tags carefully, because new cultivars vary in their mature size.