Flat-topped aster
Doellingeria umbellata · Asteraceae
Tall, leafy stems end in wide, flat heads of small white daisies with yellow centres, from late summer.
- Size
- 5 ft tall, 3 ft wide
- Zones
- 3 to 8
- Light
- Full sun to part sun
- Flowers
- Early August to mid September
- Pets
- No toxicity recorded
- Job in a bed
- Drift
A bed built around flat-topped aster
The planner designed this bed around flat-topped aster when this page was made: a 12 × 6 ft (3.7 × 1.8 m) naturalistic planting in zone 6, full sun. It chose the other plants from the 966 that suit those conditions, and says below why flat-topped aster stands where it does.
The plants
- 1 Flat-topped aster × 1, white
- 2 Stemless gentian × 22, blue
- 3 Dianthus 'Kahori' × 7, pink
- 4 False sunflower 'Summer Sun' × 3, yellow
- 5 Gray's sedge × 3, green
- 6 Palm sedge × 4, green leaves
- 7 Tiger lily × 1, orange
- 8 Grecian windflower × 8, blue
Why this plant
- The only flat plates. The others are trumpets, open bowls, daisies and others. Shape reads at a distance, where colours blur.
- The only white. White sits between stronger colours and calms them.
Why here
- Anchors a back corner. At 5 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 Gray's sedge (2½ ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- One plant, alone. A feature plant is seen as an object, and needs clear ground around it.
Why now
- In flower for 7 weeks. From early August to mid September.
- Closes the season. For its last two weeks nothing else on the plan is in flower.
Planned as a naturalistic planting: low grasses and groundcovers, the matrix, make up 59% of the planted ground. Flat-topped aster and false sunflower 'Summer Sun' anchor the back corners of the bed: the tallest plants on the plan stand there. The bed is balanced: the left half carries 48% of the visual weight and the right half 52%.
The planner's own design check: 9 Excellent, 7 Good, 1 Satisfactory.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where flat-topped aster goes in a border
At 5 ft it belongs at the back of a bed. In the planner's ten height classes it is tall (4 to 5 ft).
Its job: drift. Planted in a small group of three or five, and repeated further along in the other number.
It flowers before the other tall asters and bridges summer and autumn in a damp border. The flat heads repeat the shape of Joe-Pye weed in white.
- Rain gardens and damp meadows
- Native planting for pollinators
- The back of a moist border
What to plant with flat-topped aster
Plants recorded as good partners for it, and what each pairing does:
- Joe Pye weed 'Gateway': in flower together for six weeks, from early August; bold leaves against its medium ones; happy in the same moist soil.
- New York ironweed: in flower together for seven weeks, from early August; happy in the same moist soil.
- Swamp milkweed: happy in the same moist soil.
Questions about flat-topped aster
Does flat-topped aster need sun or shade?
Flat-topped aster grows in full sun (6 or more hours of direct sun a day) and part sun (4 to 6 hours of sun, including some afternoon sun).
It wants soil that stays evenly moist, of average fertility, and a good soak in dry spells.
What zones does flat-topped aster grow in?
USDA zones 3 to 8. It is hardy to zone 3, which means it survives winter nights down to about −30 °F (−34 °C).
Above zone 8 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does flat-topped aster flower in my zone?
In zone 5 it flowers early August to mid September. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 3 | Mid August to mid September |
|---|---|
| Zone 4 | Mid August to mid September |
| Zone 5 | Early August to mid September |
| Zone 6 | Early August to mid September |
| Zone 7 | Early August to mid September |
| Zone 8 | Early August to mid September |
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 flat-topped aster be planted?
2½ ft (75 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 3 ft (90 cm), so a group knits into one patch.
It grows 5 ft (150 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many flat-topped aster plants do I need?
At 2½ ft apart, set out in staggered rows:
- 2 to fill 10 square feet (about 1 m²)
- 5 for a single row 10 ft (3 m) long
- 6 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as a group of three or five, with a second group further along in the other number.
In the bed above, the planner used one in one group.
Is flat-topped aster 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 flat-topped aster?
They may. NC State does not list it as resistant to deer or rabbits. Where they visit, protect it, or plant it among ones they avoid.
Will flat-topped aster spread?
It spreads sideways, by runners or roots; the risk of it taking over is moderate. Spreads by underground stems in moist soil. Divide it every few years to keep it in place.
What flowers after flat-topped aster?
Flat-topped aster is over by mid September. These start as it finishes and carry the same spot on, so it never goes flat:
- Garden chrysanthemum: from mid September to late October, 24 in tall, to stand in front of it and cover its fading stems.
- Blue wood aster: from mid September to mid October, 3 ft tall, to stand in front of it and cover its fading stems.
- Montauk daisy: from mid September to late October, 3 ft tall, to stand in front of it and cover its fading stems.
What does flat-topped aster look like in winter?
Flat-topped aster dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.
Is flat-topped aster good for bees and butterflies?
Flat-topped aster is visited by pollinators and butterflies.
It is a host plant: the caterpillars of pearl crescent feed on its leaves. A butterfly can only lay its eggs on its host plants, so these do more for it than any nectar flower.
It is native to the United States.
In these guides
- Pet-safe plants for a sunny border
- Native perennials for pollinators
- Plants for butterflies
- Tall perennials and grasses for the back of a border
- Plants for a white garden
- Host plants for the pearl crescent
Zone guides: Zone 3 · Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8
Every fact on record
- Type
- Perennial
- Size
- 5 ft (150 cm) tall, 3 ft (90 cm) wide
- Plant
- 2½ ft (75 cm) apart
- Height class
- Tall (4 to 5 ft)
- Place in the bed
- Back
- Flowers
- Early August to mid September; flat plates; white
- Leaves
- Medium texture, herbaceous; green
- Shape
- Upright, spreading
- Hardy in
- USDA zones 3 to 8
- Light
- Full sun, part sun
- Soil
- Average, evenly moist
- Water
- Moderate
- Feeding
- None needed
- Family
- Asteraceae
- Comes from
- E. Canada to U.S.A
- Attracts
- Pollinators, butterflies
- Host plant for
- Pearl crescent
Checked against NC State Extension and VASCAN (plants of Canada). 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.