How to Grow Summersweet

Sweetly scented summer-blooming flowers and seed capsules that resemble peppercorns give summersweet (Clethra alnifolia), also called sweet pepperbush, its common names. Summersweet’s airy, delicate-looking flower panicles betray its ability to prosper in challenging locations. Growing summersweet is a snap even for novice gardeners because of its adaptability and few cultural demands.

Throughout its perennial range in U.S. Department of Agriculture plant hardiness zones 3 through 9, summersweet’s cultivars offer varying heights for any size garden. If you have a small garden in USDA zones 4 through 8, grow "Crystalina" (Clethra alnifolia "Crystalina") or "Ruby Spice" (Clethra alnifolia "Ruby Spice"). "Crystalina" reaches only 2 to 3 feet with a 3- to 4-foot spread, and it has a tidy, rounded shape with white flowers. "Ruby Spice" grows a bit taller -- 4 to 6 feet -- but with a narrower spread of 3 to 5 feet, so it fills small-garden vertical spaces nicely. For smaller gardens in USDA zones 3 through 9, "Hummingbird" (Clethra alnifolia "Hummingbird") features white flowers and reaches 2 to 4 feet with a spread of 3 to 5 feet. If you have a larger garden in USDA zones 4 through 8, grow "Pink Spire" (Clethra alnifolia "Pink Spire"). This pink-flowering shrub may reach 8 feet with a 6-foot spread.

When most flowering shrubs stop blooming in late summer, summersweet is just hitting its stride. This native shrub prefers well-draining acidic soil, and it tolerates clay soil, particularly if you add ground, composted pine bark to loosen the clay. Summersweet grows and flowers in full sun or full shade, and it is salt-tolerant for growing in coastal gardens. Space summersweet depending on cultivar requirements. To accommodate the species’ spread, space plants 6 feet apart. "Crystalina" needs 4-foot spacing, "Ruby Spice" and "Hummingbird" need 5-foot spacing, and plant "Pink Spire" with 6-foot spacing between plants.

You can grow summersweet in problem areas, such as low-lying spots where rainwater collects temporarily, because it has the ability to thrive in moist but well-draining soil, which often means death to other plants. Mature plants can tolerate infrequent periods of drought, but they respond best if you keep the soil consistently moist. Before the leaf buds open in spring, apply 1 pound of 10-10-10 fertilizer around plants per 100-square-foot area, and reapply at the same rate after plants stop flowering in summer.

Summersweet is rarely bothered by any pests or disease. The shrubs keep a tidy, natural shape, so you typically won’t have to prune them unless an errant shrub grows out of its boundaries. Summersweet flowers on new wood, which means that you can prune it in later winter to early spring and it will still bloom in summer. Mature plants form plantlets around the crown, which you can remove from the parent plant and transplant elsewhere in your garden. Disinfect pruning tools by soaking them for five minutes in a solution of three parts water and one part household pine-oil cleaner, and rinse tools before cutting plants.