Summersweet
Clethra alnifolia · Clethraceae
Upright spikes of white or pink flowers with a rich, spicy fragrance in the heat of late summer. A native shrub that flowers well even in shade and in wet soil.
- Size
- 6½ ft tall, 5 ft wide
- Zones
- 3 to 9
- Light
- Full sun to part shade
- Flowers
- Mid July to mid August
- Pets
- No toxicity recorded
- Job in a bed
- Anchor
A bed built around summersweet
The planner designed this bed around summersweet when this page was made: a 16 × 8 ft (4.9 × 2.4 m) English border in zone 6, part sun. It chose the other plants from the 708 that suit those conditions, and says below why summersweet stands where it does.
The plants
- 1 Summersweet × 1, white
- 2 Stemless gentian × 27, blue
- 3 Green-and-gold × 19, yellow
- 4 White mugwort × 4, cream
- 5 Joe Pye weed 'Little Joe' × 3, pink
- 6 Japanese forest grass 'All Gold' × 8, chartreuse leaves
- 7 Asiatic lily × 4, orange
- 8 Camassia × 5, blue
- 9 Snowdrop × 7, white
Why this plant
- Part of the bed's structure. Shrubs and grasses keep their shape when the perennials die down. So does Japanese forest grass 'All Gold'.
Why here
- Anchors a back corner. At 6½ ft it is the tallest plant here, and the tallest close the ends of the bed, where they stand in front of nothing.
- A step in the back row. Next to white mugwort (5 ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- One plant, alone. A shrub is seen as an object, and needs clear ground around it.
Why now
- In flower for six weeks. From mid July to mid August.
- Fills a gap. For one of those weeks nothing else on the plan is in flower.
Planned as an English border: 9 of the 9 groups (100%) are drifts, longer along the bed than they are deep. The flowers run from early March to mid September, but stop for 3 weeks from early April. Neither end outweighs the other: the visual weight is split 53 to 47, left to right.
The planner's own design check: 12 Excellent, 3 Good, 2 Satisfactory.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where summersweet goes in a border
At 6½ ft it belongs at the back of a bed. In the planner's ten height classes it is very tall (5 to 6½ ft).
Its job: anchor. A shrub that gives the bed permanent structure. Planted singly, as soon as the front edge is laid; everything else is arranged around it.
Few shrubs flower in shade in August, and fewer smell this good. The leaves turn gold in autumn. It suckers gently into a colony.
- Fragrance in late summer
- Shade and wet soil
- Bees and butterflies
What to plant with summersweet
Plants recorded as good partners for it, and what each pairing does:
- Ostrich fern: its green leaves are a setting for the flowers, before and after; low enough (4 ft) to stand in front of it.
- Hosta: its green leaves are a setting for the flowers, before and after; bold leaves against its medium ones; a low mound at the foot of its spires.
- Astilbe: in flower together for two weeks, from mid July; low enough (24 in) to stand in front of it; happy in the same moist soil.
Choosing between it and a look-alike? Butterfly bush vs Summersweet.
Questions about summersweet
Does summersweet need sun or shade?
Summersweet grows in full sun (6 or more hours of direct sun a day), part sun (4 to 6 hours of sun, including some afternoon sun) and part shade (2 to 4 hours of sun, mostly in the morning). It is one of the few that also put up with deep shade.
It wants soil that stays evenly moist, of average fertility, and a good soak in dry spells. It copes with soil that stays wet.
What zones does summersweet grow in?
USDA zones 3 to 9. It is hardy to zone 3, which means it survives winter nights down to about −30 °F (−34 °C).
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does summersweet flower in my zone?
In zone 5 it flowers mid July to mid August. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 3 | Mid July to late August |
|---|---|
| Zone 4 | Mid July to late August |
| Zone 5 | Mid July to mid August |
| Zone 6 | Mid July to mid August |
| Zone 7 | Early July to early August |
| Zone 8 | Early July to early August |
| Zone 9 | Late June to early August |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should summersweet be planted?
4 ft (120 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 5 ft (150 cm), so a group knits into one patch.
It grows 6½ ft (200 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many summersweet plants do I need?
Usually one. At 4 ft (120 cm) across, it is a plant you place, not one you mass. For a hedge or screen, set them 4 ft apart: three plants for a 10 ft run.
In the bed above, the planner used one in one group.
Is summersweet poisonous to dogs and cats?
No toxicity is recorded for dogs, cats, horses or people, according to NC State Extension.
"Not toxic" is not "edible": a pet that eats a lot of any plant can be sick.
Do deer eat summersweet?
Mostly not. NC State lists it as resistant to deer. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.
Will summersweet spread?
It spreads sideways, by runners or roots; the risk of it taking over is moderate. Spreads by suckers into a wider clump. Remove the outer shoots to contain it.
What flowers after summersweet?
Summersweet is over by mid August. These start as it finishes and carry the same spot on, so it never goes flat:
- Japanese anemone: from mid August to early October, 3 ft tall, to stand in front of it and cover its fading stems.
- Switchgrass 'Northwind': from early August to early October, 5½ ft tall.
- Garden chrysanthemum: from mid September to late October, 24 in tall, to stand in front of it and cover its fading stems.
What does summersweet look like in winter?
Summersweet drops its leaves and stands as bare branches. That is when to see its shape, and to prune it if it needs pruning.
Is summersweet good for bees and butterflies?
Summersweet is visited by pollinators, bees, specialist bees, butterflies, hummingbirds and songbirds.
It is native to the United States and Canada.
More Clethra
- Summersweet 'Hummingbird' Clethra alnifolia 'Hummingbird'
- Summersweet 'Ruby Spice' Clethra alnifolia 'Ruby Spice'
In these guides
- Plants for deep shade
- Plants for wet soil and rain gardens
- Salt-tolerant plants for roadsides and coasts
- Plants for slopes and banks
- Deer-resistant plants for shade
- Pet-safe plants for a sunny border
- Pet-safe plants for shade
- Native plants for shade
- Garden plants native to Canada
- Plants for hummingbirds
- Plants for butterflies
- Plants for bees
- Plants that feed garden birds
- Plants with spires: vertical accents
- Plants for a white garden
Zone guides: Zone 3 · Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8 · Zone 9
Every fact on record
- Type
- Shrub
- Size
- 6½ ft (200 cm) tall, 5 ft (150 cm) wide
- Plant
- 4 ft (120 cm) apart
- Height class
- Very tall (5 to 6½ ft)
- Place in the bed
- Back
- Flowers
- Mid July to mid August; upright spires; white, pink
- Leaves
- Medium texture, deciduous; dark green
- Shape
- Upright, spreading
- Hardy in
- USDA zones 3 to 9
- Light
- Full sun, part sun, part shade
- Soil
- Average, evenly moist
- Water
- Moderate
- Feeding
- None needed
- Family
- Clethraceae
- Comes from
- Eastern North America
- Attracts
- Pollinators, bees, specialist bees, butterflies, hummingbirds, songbirds
- Stands up to
- Deer, salt, wet soil, deep shade, erosion
Checked against NC State Extension. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.