Shrub · Clethraceae
Summersweet
Clethra alnifolia
Give it steady moisture and a little shade, and summersweet rewards you with fragrant spikes when most shrubs have quit for the year.
Partial shade
Every 3–7 days
USDA 3–9
3–8 ft · 0.9–2.4 m
Overview
Summersweet is a native shrub that earns its name in July and August, when bottlebrush spikes of fragrant white or pink flowers open just as the rest of the garden winds down. It belongs to the Clethraceae family and grows wild along the eastern seaboard in damp woods and along stream edges. That swampy heritage is the key to it, because this is a shrub that actually wants wet feet.
It's an easy plant to live with. Hardy across a wide stretch of cold, from zone 3 through zone 9, it shrugs off harsh winters and tolerates clay, salt, and standing water that would sink most shrubs. The flowers pull in bees and butterflies all summer, and the foliage turns a clean golden yellow before it drops in fall.
Give it the moist, acidic ground it likes and it asks for almost nothing else. The one thing it won't forgive is a hot, dry site, where the leaves bronze and spider mites move in. Plant it somewhere damp with a bit of afternoon shade and it spreads into a fragrant, fuss-free colony.
Care
The short version: partial shade to full sun, in moist to wet, acidic soil that never dries out. Keep it watered through heat, prune in late winter, and feed once in spring.
Light
Summersweet does best in partial shade but takes everything from full sun to deeper shade. It flowers more freely with some direct light, yet keeps blooming where many shrubs would give up, which makes it a rare choice for a shadier corner.
Water
Keep the soil evenly moist to wet and never let it bake dry. Water every 3 to 7 days, and more often while a new plant is establishing or during a dry spell. This is a streamside shrub at heart, so wet feet suit it far better than thirst.
Soil
Plant it in moist to wet, acidic ground rich in organic matter. A pH from 4.5 to 7.0 covers it, and unlike fussier shrubs it handles heavy clay and soggy, low-lying spots without complaint.
Temperature
Cold is no obstacle here. The shrub is hardy from roughly -29°F to 100°F (-34°C to 38°C), which carries it through zone 3 winters and southern summers alike.
Humidity
Ordinary outdoor humidity is all it needs, so there's no number to manage. What matters is moisture at the roots, since dry air paired with dry soil is what invites spider mites.
Feeding
One spring feeding is plenty. Use a balanced or acidifying fertilizer made for acid-loving plants to keep the soil on the sour side it prefers.
Pruning
Because it blooms on new wood, prune in late winter or early spring to shape it and hold its size without losing any flowers. Pull off the root suckers too, unless you're happy to let it spread into a colony.
Repotting
Grown in the ground, summersweet rarely needs anything done to its roots. In a container, repot only when roots circle the pot, push out the drainage holes, or water runs straight through without soaking in.
Size & spacing
A mature shrub stands 3 to 8 feet (91 to 244 cm) tall and spreads 4 to 6 feet (122 to 183 cm) wide. Give it room for that full width, and keep in mind it will sucker outward beyond the original plant.
When to plant
Summersweet goes in the ground in spring or fall, while the weather is mild and the roots can settle before the next stretch of heat or cold. The fragrant flowers follow 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
Almost everything that troubles summersweet comes back to one thing: a site that's too hot and too dry. Read the leaves early and most problems fix themselves once the moisture is right. Match what you see below, then act before the stress sets in.
Stippled, bronzing leaves with fine webbing
This is spider mites, and they move in when a plant sits too hot and too dry. Blast the leaves with a hard spray of water to knock them loose, then keep the soil moist so the plant stops drawing them in. Insecticidal soap or horticultural oil clears a heavier run if the spray alone falls short.
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 in a hot, dry spot
This is drought stress, and it traces back to the planting site more than anything you've done. Summersweet wants steady moisture and turns sad fast in dry heat. Water more often to keep the root zone evenly moist, lay down mulch to hold what's there, and move a chronically stressed shrub to a cooler, damper, partly shaded spot.
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 for households with animals and small children. Summersweet is not on the ASPCA toxic-plant lists and is treated as non-toxic and pet-safe. The worst a stray nibble might do is a brief, mild stomach upset, the same as with almost any garden plant.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Summersweet is safe for cats and isn't on the ASPCA toxic list. A cat that nibbles a leaf might get a brief upset stomach, the same as with any plant, but nothing worse.
Dogs None
Dogs can share the garden with no worry here. The shrub carries no known toxin, though wolfing down a big mouthful of foliage may bring on a little drooling or a loose stool.
Horses Safe
Horses are fine around summersweet, with no toxic compounds to cause harm. A few leaves browsed in passing won't trouble them.
Rabbits Safe
Rabbits can graze near the plant safely. It holds nothing poisonous, so a stray bite of leaf does no damage.
Livestock Safe
Cattle, goats, and sheep can pasture beside summersweet without risk. The foliage is free of the toxins that trouble grazing animals.
Birds Safe
Backyard and wild birds are safe around the shrub, which often draws bees and butterflies to its fragrant spikes. Nothing on the plant poses a hazard to them.
People Safe
Summersweet is not toxic to people. It isn't grown to be eaten, but a curious child who tastes a leaf faces nothing more than a possible mild stomach ache.
As with any plant, ingestion of large amounts of plant material may cause mild, transient stomach upset.
Varieties
Several named selections of summersweet turn up at nurseries, sorted mostly by size and flower color. These are the ones worth knowing.
Hummingbird
A compact dwarf that stays around 2 to 4 feet tall and packs on dense white flower spikes.
Ruby Spice
Its deep pink flowers hold their color all through bloom instead of washing out.
Pink Spire
Pink buds open into pale pink, fragrant spikes.
Sixteen Candles
Upright white spikes stand well above the foliage on a tidy, compact frame.
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
Summersweet is simple to multiply, and the suckering habit that some gardeners fight is exactly what makes free plants so easy to come by.
DivisionEasy
Late winter to early spring · 1 to 2 growing seasons
The easiest route is to split off the rooted suckers that crop up around the edge of a colony. Lift them in late winter or early spring and replant, and they settle into a full shrub over 1 to 2 growing seasons.
Stem cuttingsModerate
Early summer (softwood) · Several weeks to root, then 1 season to establish
Take softwood cuttings in early summer and root them under mist or a humidity cover. They throw roots in a few weeks and need about a season after that to establish.
SeedModerate
Sow collected seed in fall or after cold stratification · 1 to 2 seasons
Surface-sow the fine seed in fall or after a cold-stratification period, since it needs light and chilling to wake up. Plan on 1 to 2 seasons to a usable plant, and remember that named cultivars won't come true this way.
Myths
Summersweet only blooms well in full sun.
It's one of the few flowering shrubs that flowers reliably in part shade. You still get fragrant, late-summer spikes in spots where most shrubs would sulk.
Prune summersweet right after it flowers to get more blooms.
It blooms on new, current-season wood, so the right time to prune is late winter or early spring. Cutting it then takes nothing from the coming season's flowers.