Sweet-Scented August: Clethra Alnifolia

August 17th, 2009 § 4 comments

Clethra alnifolia, North American native “Sweet Pepperbush’

Some of the most beautiful late-blooming shrubs remind me of that childhood tale, “The Ugly Duckling”. Late to leaf out, looking perhaps a bit twiggy and awkward in June, these stars of the late summer garden take their time dressing up for spring. Sweet pepperbush is one of those shrubs. Personally, I never mind shyness, in fact I often find it quite charming. Besides, it’s like they always say, good things often come to those who wait. And in the case of Clethra alnifolia, that old adage couldn’t be more true. This late blooming beauty produces some of the most fragrant flowers in my garden; attracting butterflies, bees, hummingbirds and humans alike. But when most gardeners are out shopping in early spring, Clethra alnifolia is looking a bit scrappy. Lilac, azalea and roses are scooped up at garden centers by the cart-full, while the sweet pepperbush languishes in the corner like a high school wall-flower. It seems like her only fans are horticultural-geeks, (always quick notice her).

Well, don’t you be fooled by the awkward-spring-nature of this gorgeous native plant. Clethra is a knock-out worth waiting for. Just like that skinny girl at the prom, (you remember the one with the metallic braces?), Clethra makes up for lost time a bit later on in the season, when you will be glad you chose her. When the perky roses are past their prime and that showy azalea starts to look a bit shabby, Clethra’s lustrous green leaves still shimmer and shine in the late summer heat. Then, round about August, Clethra really comes into her own. Oh the flowers!  The sweet smell of pepperbush is a fragrance you will never forget. Borne on the current season’s new growth, the elegant blossoms cluster on upright racemes or panicles, often 8-12″ in length. Bloom time begins in late July or early August and continues for at least 4-6 weeks, (longer when sited in a moist location with partial shade). And there are so many new cultivars! ‘Ruby Spice’ and ‘Pink Spires’ bloom in glorious shades soft pink rarely seen so late in the season, and creamy ‘September Beauty’ extends the spicy-fragrance right into October here at Ferncliff.

Clethra alnifolia ‘Ruby Spice’ in mid-August at Ferncliff

Come autumn, the foliage of Clethera alnifolia turns a gorgeous shade of golden yellow, slowly burnishing to a warm, coppery brown. What beauty! I like to surround Clethra with late blooming blue-violet asters, such as Aster oblongifolium, ‘Raydon’s Favorite’, and violet-blue Aconitum (Monk’s Hood). Placing violet against the gold is a great way to bring out the intensity of both colors. Because of its honey gold autum foliage, Clethra also looks beautiful when planted near darker foliage shrubs such as purple-leafed Cotinus, and Physocarpus cultivars ‘Diabolo’, ‘Coppertinia’, and ‘Summer Wine’. The multicolored autumn leaves of Fothergilla gardenii and many Viburnum cultivars also make great border-mates for Clethra alnifolia.

And now, at the risk of sounding like an infomercial, is the time when I say : “but wait… that’s not all”! Because Clethra alnifolia is a native to North America, growing this shrub is one of the kindest things you can do for late season bees, butterflies and birds. Since many suburban gardeners lean toward spring-blooming shrubs in their planting schemes, few backyard food sources remain for our pollen-dependent friends in the latter part of the season. By choosing late-blooming shrubs and perennials, a gardener can help give back some of the natural habitat we humans have taken away with our subdivisions, lawns and hardscaping. Not only will you enjoy the fragrance of sweet pepperbush in your garden, but the hummingbirds, bees and butterflies will delight in Clethra’s sweet elixir.

Ready to add sweet pepperbush to your garden? Like most ‘ugly-duckings’ Clethra alnifolia has an easy-going personality. And, as is the case with many native plants, this is generally a pest-free shrub with few diseases. Keep in mind Clethra’s needs and you won’t be disappointed. The sweet pepperbush is native to woodlands and swamps from Nova Scotia on south to Florida, (zone 4 – 9). As such a plant, Clethra prefers semi-moist, slightly acidic soil conditions, (though average, well prepared and mulched garden soil will do fine). Also a plus, Clethra can tolerate a bit of shade from taller shrubs or trees. But do keep in mind, this is a suckering shrub, so give it plenty of room to spread out, (cultivars vary in size from small to large, but the species can grow from 4-12′ high and 6-10′ wide or more). Because the blossoms of sweet pepperbush occur on new-growth late in the season, any pruning should take place in the early part of the year,(ideally before June 1st). Be certain to make shallow-angled cuts on the alternate leafed branches, just above an outward facing leaf-bud. Clethra alnifolia forms a loose, natural-looking hedge when planted in groups, and except for the removal of spent blossoms, I avoid most pruning. However, should you find that your sweet pepperbush gets a bit wild and unruly, a severe pruning in early spring will rejuvenate her beauty. To my eye, Clethra alnifolia is always the perfect garden swan.

Clethra alnifolia, ‘Ruby Spice’ in bud at Ferncliff


Article and Photographs Copyright 2009 Michaela at The Gardener’s Eden


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§ 4 Responses to Sweet-Scented August: Clethra Alnifolia"

  • Deb says:

    I have this beautiful shrub planted outside my living room window; when the wind is blowing from the southwest the fragrance fills the room. I wish it wasn’t a suckering shrub – it’s hard to keep up with all those shoots especially as I get busy with other things during the summer. Mine seems to attract an odd flying insect that eats the blossoms. It’s black with two body parts and looks something like a large hornet. When I mow the lawn near the shrub, they come out in a swarm but don’t attack. Do you have any idea what they might be? I did some research and came up with a Japanese hornet but am not sure if those are found this far north (in NH).

  • admin says:

    Hi Deb, I suspect that what you have is an organ pipe wasp, (trypoxyion politum), a mud dauber. I have seen these on Clethera alnifolia in August-September. Pipe wasps are capable of stinging, but rarely do so. They are actually considered beneficial insects, (pollinators). So, I know they are a bit disturbing, but google that insect. If it looks familiar, he is actually a friend. Like a snake, he may be a bit startling, but is not intending to harm you. Now, I am not an entomologist, but I have a fairly good grasp on this and I think this is the case. As for the suckering issue… I would suggest a sharp edger. Use this tool to cut the Clethera root and keep it in check. Your shrub is a good friend, and clearly happy in it’s situation. If you have a friend in need of native plants, share the wealth. Let me know about the entomological question. If I am incorrect, please send me a photo… as I am curious as you are. And thank you for writing !
    All the best,
    Michaela at The Gardener’s Eden

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