Summersweet will sweeten your late summer garden.
There aren’t many shrubs or trees that flower in mid to late summer after the first clamor of bloom is over. Clethra alnifolia, also known as summersweet or sweet pepper bush, is an exception.
Growing to 8 feet tall in USDA zones 3 through 9, it makes spires of spicily sweet-scented white or pink flowers from about mid-July to summer's end. Blooming on new wood, it doesn’t mind spring pruning and its alder-like foliage turns gold in autumn. Because it originated in wet woodlands, summersweet also will tolerate shade and soggy soil better than most shrubs do, and its flowers are highly attractive to bees and butterflies, its peppercorn-like seedpods alluring to birds.
It does have its downsides, though. Because it tends to leaf out late--sometimes not until the end of May—it will look bare in spring. And a couple Dave’s Gardeners report that it also suckers freely enough to be highly invasive for them.
Not everyone has that problem with it. But, since my experience with the rampant growth of false spirea—which ran roughshod over several of my rose bushes, I tend to be wary of shrubs that sucker. And I’ve always found white-flowered plants to be more vigorous than those with deeper hues, sometimes too much so!
As summersweet also comes in pink cultivars, such as ‘Ruby Spice,’ I could opt for one of them in hopes of containing that vigor a bit. Or I could try the taller Japanese sweet shrub (Clethra barbinervis), suited to USDA zones 5 through 8. Capable of reaching 20 feet in height, it is supposed to be only marginally hardy here in zone 5, so the cold might help keep it in check. Its scent isn’t as strong as alnifolia’s and its flower spikes are more horizontal, but it also boasts attractively peeling bark.
As luck would have it, the clethra which I find most lovely is the one which isn’t hardy in my zone. The lily of the valley tree (Clethra arborea) can reach 20 feet with glossy, evergreen leaves and clusters of flowers which resemble those of its namesake. Also known as white alder, it generally only thrives in zones 9 through 11.
Almost all of the sweet shrubs or trees prefer partial shade and moist but well-drained acidic soil. However, they can grow happily in full sun or full shade too, though overly alkaline soil may give them pause.
Summersweet’s tiny red seeds reportedly don’t require stratification (freezing or refrigeration), but germinate best in cool temperatures, at about 55 degrees Fahrenheit. As with most tiny seeds, you either should just press them into the surface of your seed-starting mix or cover them only very lightly. They may take a month or more to sprout.
The shrub is supposed to grow easily from cuttings, with one source reporting that cuttings started in spring could be 16 inches tall and blooming by late summer. “Once bitten” gardeners like me are inclined to view such vim with suspicion, but it can be a good thing--as long as you keep summersweet in an area where it can spread without bullying other bushes.
Photos: The banner photo is by plantdude, the second photo by RosinaBloom, and the final two by growin, all from the Dave's Garden PlantFiles.