Shrub · Clethraceae
Summersweet
Clethra alnifolia
Give it steady moisture and a bit of shade, and summersweet pays you back with fragrant spikes long after the other shrubs have packed it in.
Partial shade
Every 3–7 days
USDA 3–9
3–8 ft · 0.9–2.4 m
Overview
Summersweet really lives up to its name in July and August, when bottlebrush spikes of fragrant white or pink flowers open up just as everything else in the garden is winding down. It's part of the Clethraceae family, and it grows wild along the eastern seaboard in damp woods and along stream edges. So what's the secret to keeping it happy? That swampy background, because this is a shrub that genuinely likes wet feet.
It's honestly an easy plant to live with. It's hardy across a big range of cold, from zone 3 all the way to zone 9, so it laughs off tough winters and puts up with clay, salt, and standing water that would drown most shrubs. The flowers keep bees and butterflies coming all summer, and the leaves turn a clean golden yellow before they drop in fall.
Give it that moist, acidic ground it loves and it barely asks for anything else. The one thing it won't put up with is a hot, dry spot, where the leaves bronze and spider mites move in. Plant it somewhere damp with a little afternoon shade, though, and it'll spread into a fragrant, easygoing colony.
Care
The short version: partial shade to full sun, in moist to wet, acidic soil that never dries out, watered through the heat, pruned in late winter, and fed just once in spring.
Light
Summersweet is happiest in partial shade, but it'll take anything from full sun to deeper shade. Sure, it flowers a bit more with some direct light, yet it keeps blooming where a lot of shrubs would just quit, which makes it a great pick for a shadier corner.
Water
Keep the soil evenly moist to wet and don't ever let it bake dry. Water it every 3 to 7 days, and more often while a new plant's settling in or during a dry spell. Remember, it's a streamside shrub at heart, so wet feet suit it way better than going thirsty.
Soil
Plant it in moist to wet, acidic ground that's got plenty of organic matter. A pH anywhere from 4.5 to 7.0 works, and unlike fussier shrubs it handles heavy clay and soggy, low-lying spots just fine.
Temperature
Cold's really not an issue here. The shrub's hardy from about -29°F to 100°F (-34°C to 38°C), so it sails through zone 3 winters and hot southern summers alike.
Humidity
Regular outdoor air is all it wants, so there's no number to worry about. What actually matters is moisture at the roots, since dry air plus dry soil is what invites spider mites in.
Feeding
One feeding in spring is plenty. Just use a balanced or acidifying fertilizer made for acid-loving plants, which keeps the soil on the sour side it likes.
Pruning
Since it blooms on new wood, prune it in late winter or early spring to shape it and keep the size down without losing any flowers. Pull off the root suckers too, unless you're happy to let it spread into a colony.
Repotting
Out in the ground, summersweet hardly ever needs anything done to its roots. In a pot, only repot when the roots circle around, poke out the drainage holes, or water runs straight through without soaking in.
Size & spacing
A grown shrub gets about 3 to 8 feet (91 to 244 cm) tall and spreads 4 to 6 feet (122 to 183 cm) wide. Leave room for that full width, and don't forget it'll sucker outward past where you first planted it.
When to plant
Summersweet goes in the ground in spring or fall, while it's mild out and the roots can settle before the next round of heat or cold. And the fragrant flowers? They show up on their own in July and August, on growth the plant makes that same year.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring or fall
- Harvest: July to August
Hardiness
USDA hardiness zones: 3–9
Temperature: down to -40°C
Troubleshooting
Just about everything that bugs summersweet comes back to one thing: a spot that's too hot and too dry. Read the leaves early and most of the trouble sorts itself out once the moisture's right. Find what matches what you're seeing below, then act before the stress digs in.
Speckled, bronzing leaves with a bit of webbing
What you're looking at is spider mites, and they show up when a plant's been sitting somewhere too hot and too dry. The quick fix? Hose the leaves down hard to knock the mites off, then keep the soil moist so the shrub quits inviting them back. If a bad patch hangs on, insecticidal soap or horticultural oil will mop up what's left.
Fix:
- Spray foliage with a strong stream of water to dislodge mites
- Improve soil moisture and avoid hot, dry sites
- Apply insecticidal soap or horticultural oil to affected foliage if needed
Wilting and yellowing where it's hot and dry
This one's drought stress, and honestly it's about where the shrub is planted more than anything you've done. Summersweet wants steady moisture, so it goes downhill fast in dry heat. Water it more often to keep the roots evenly damp, throw some mulch down to hold that moisture in, and if the same shrub keeps sulking, move it somewhere cooler, damper, and partly shaded.
Fix:
- Increase watering frequency to keep soil evenly moist
- Mulch to conserve moisture and keep roots cool
- Relocate to a moister, partly shaded site if chronically stressed
Toxicity
Good news if you've got pets or little kids around. Summersweet isn't on the ASPCA toxic-plant lists, so it's treated as non-toxic and pet-safe. The worst a stray nibble is likely to do is cause a quick, mild tummy upset, which is true of almost any garden plant.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Got a cat? No problem here, since summersweet isn't on the ASPCA toxic list. If a cat chews on a leaf, the worst that's likely to happen is a quick upset stomach, which is pretty much true of any plant.
Dogs None
Dogs are welcome to hang out in the garden with this one. There's no known toxin in the shrub, though a dog that scarfs a big mouthful of leaves might drool a little or have a loose stool for a bit.
Horses Safe
Horses do just fine around summersweet, since there's nothing harmful in it. A couple of leaves nibbled while they graze won't bother them one bit.
Rabbits Safe
Rabbits can munch near the plant and stay perfectly fine. Nothing on it is poisonous, so a stray bite of leaf isn't going to hurt them.
Livestock Safe
Cattle, goats, and sheep can graze right next to summersweet, no worries. The leaves don't carry the toxins that usually cause trouble for grazing animals.
Birds Safe
Birds, whether they're yours or just passing through, are safe around the shrub, and it's a magnet for bees and butterflies thanks to those fragrant spikes. Nothing on the plant is going to hurt them.
People Safe
People are fine around summersweet too. It isn't something you'd grow to eat, but if a curious kid tastes a leaf, the most they'll get is maybe a mild tummy ache.
As with any plant, ingestion of large amounts of plant material may cause mild, transient stomach upset.
Varieties
A few named summersweet selections show up at nurseries, mostly sorted by size and flower color. Here are the ones worth knowing about.
Hummingbird
It's a little compact dwarf that stays around 2 to 4 feet tall and just piles on the dense white flower spikes.
Ruby Spice
Its deep pink flowers actually hold that color all the way through bloom instead of washing out pale.
Pink Spire
The pink buds open up into soft pink, fragrant spikes.
Sixteen Candles
It sends up neat white spikes that stand well above the leaves on a nice compact shrub.
Companions
Summersweet pairs best with other natives that share its love of wet, acidic ground, the kind of partners that thrive in a rain garden or a damp, shaded border.
Plant near
Itea virginica (Virginia sweetspire): Shares the same moist, acidic soil and sun-to-part-shade conditions for wet-site and rain-garden plantings.
Ilex verticillata (winterberry): Native shrub that thrives in the same wet to moist soils and pairs well in naturalized and pollinator plantings.
How to propagate
Making more summersweet is pretty simple, and that suckering habit some gardeners grumble about? That's exactly what makes free plants so easy to come by.
DivisionEasy
Late winter to early spring · 1 to 2 growing seasons
The easy way? Just split off the rooted suckers that pop up around the edge of a clump. Dig them out in late winter or early spring, replant them, and they'll grow into a full shrub over 1 to 2 growing seasons.
Stem cuttingsModerate
Early summer (softwood) · Several weeks to root, then 1 season to establish
Want to try cuttings? Snip some soft new growth in early summer and root it under mist or a humidity cover. It'll put out roots in a few weeks, and then it needs about a season to really settle in.
SeedModerate
Sow collected seed in fall or after cold stratification · 1 to 2 seasons
Sprinkle the fine seed on the surface in fall, or after a cold-stratification spell, because it needs both light and a chill before it'll sprout. Figure on 1 to 2 seasons to a decent plant, and keep in mind that named cultivars won't come true from seed.
Myths
Summersweet only blooms well in full sun.
Not true, since it's one of the few flowering shrubs that blooms reliably in part shade. You'll still get fragrant, late-summer spikes in the kind of spots where most shrubs would just sulk.
Prune summersweet right after it flowers to get more blooms.
Here's the thing: it blooms on new, current-season wood, so the right time to prune is late winter or early spring. Cut it back then and you lose none of the coming season's flowers, which is exactly what you want.