Blue mistflower
Conoclinium coelestinum · Asteraceae
Fluffy, lavender-blue flower heads, like a tall ageratum, in early autumn. A native that spreads fast by runners in moist soil.
- Size
- 2½ ft tall, 2½ ft wide
- Zones
- 5 to 10
- Light
- Full sun to part sun
- Flowers
- Late August to mid October
- Pets
- No toxicity recorded
- Job in a bed
- Drift
A bed built around blue mistflower
The planner designed this bed around blue mistflower 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 blue mistflower stands where it does.
The plants
- 1 Blue mistflower × 3, blue
- 2 Mountain avens × 10, white
- 3 Mouse-ear coreopsis 'Nana' × 3, yellow
- 4 Northern sea oats × 3, tan
- 5 Globe arborvitae 'Danica' × 1, green leaves
- 6 Gloriosa daisy × 4, orange
- 7 Oriental lily × 4, pink
- 8 Hyacinth × 10, purple
Why this plant
- The only dense clusters. The others are open bowls, daisies, airy sprays and others. Shape reads at a distance, where colours blur.
- The only blue.
Why here
- At the back. At 2½ ft it stands ahead of oriental lily (4 ft) without hiding it.
- A step in the back row. Next to oriental lily (4 ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- 3 plants in one group. Massed, one kind reads as a single shape. Scattered, it would look spotty.
Why now
- In flower for 7 weeks. From late August to mid October.
- Closes the season. For its last three weeks nothing else on the plan is in flower.
Planned as a naturalistic planting: low grasses and groundcovers, the matrix, make up 49% of the planted ground. Mountain avens is planted in three places along the bed, which gives it rhythm. The most in flower at one time is 3 kinds, from early August.
The planner's own design check: 10 Excellent, 6 Good, 1 Satisfactory. It flags one thing to watch: Oriental lily is highly poisonous to cats. Blue mistflower spreads aggressively.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where blue mistflower goes in a border
At 2½ ft it belongs in the middle of a bed. In the planner's ten height classes it is medium (24 in to 2½ ft).
Its job: drift. Planted in a small group of three or five, and repeated further along in the other number.
Blue-violet beside the gold of goldenrod is the natural colour scheme of the autumn roadside, and worth copying. It is too invasive at the root for a small bed: give it a wild corner.
- Autumn blue for moist, wild areas
- Butterfly gardens
- Naturalising with goldenrods
What to plant with blue mistflower
Plants recorded as good partners for it, and what each pairing does:
- Goldenrod 'Fireworks': blue against yellow, opposite each other on the colour wheel, in flower together for seven weeks.
- New England aster: in flower together for six weeks, from early September; tall enough (4 ft) to stand behind it; happy in the same moist soil.
- Swamp milkweed: flowers first, early July to early August, so the spot is never empty; tall enough (4 ft) to stand behind it; happy in the same moist soil.
Questions about blue mistflower
Does blue mistflower need sun or shade?
Blue mistflower 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. It copes with soil that stays wet.
What zones does blue mistflower grow in?
USDA zones 5 to 10. It is hardy to zone 5, which means it survives winter nights down to about −10 °F (−23 °C).
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does blue mistflower flower in my zone?
In zone 5 it flowers late August to mid October. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 5 | Late August to mid October |
|---|---|
| Zone 6 | Late August to mid October |
| Zone 7 | Late August to mid October |
| Zone 8 | Late August to mid October |
| Zone 9 | Mid August to mid October |
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 blue mistflower be planted?
24 in (60 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 2½ ft (75 cm), so a group knits into one patch.
It grows 2½ ft (75 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many blue mistflower plants do I need?
At 24 in apart, set out in staggered rows:
- 3 to fill 10 square feet (about 1 m²)
- 6 for a single row 10 ft (3 m) long
- 10 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 three in one group.
Is blue mistflower 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 blue mistflower?
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 blue mistflower spread?
It spreads sideways, by runners or roots; the risk of it taking over is high. Spreads aggressively by runners in moist soil, and seeds about. Plant it only where it can roam.
What flowers after blue mistflower?
Blue mistflower is over by mid October. These start as it finishes and carry the same spot on, so it never goes flat:
- Japanese onion 'Ozawa': from early October to early November, 10 in tall, to stand in front of it and cover its fading stems.
- Tatarian aster 'Jindai': from early October to early November, 4 ft tall.
- Bodnant viburnum 'Dawn': from early November to late December, 10 ft tall.
What does blue mistflower look like in winter?
Blue mistflower dies down, but leave the stems standing: the seed heads stand through the winter, and songbirds eat the seed. Cut them down in early spring, before the new shoots come.
Is blue mistflower good for bees and butterflies?
Blue mistflower is visited by pollinators, butterflies, moths and songbirds.
It is native to the United States.
In these guides
- Plants for wet soil and rain gardens
- Deer-resistant perennials for full sun
- Pet-safe plants for a sunny border
- Native perennials for pollinators
- Plants for butterflies
- Plants that feed garden birds
- Plants that flower in fall
- Plants with blue flowers
Every fact on record
- Type
- Perennial
- Size
- 2½ ft (75 cm) tall, 2½ ft (75 cm) wide
- Plant
- 24 in (60 cm) apart
- Height class
- Medium (24 in to 2½ ft)
- Place in the bed
- Middle
- Flowers
- Late August to mid October; dense clusters; blue
- Leaves
- Medium texture, herbaceous; green
- Shape
- Upright, spreading
- Hardy in
- USDA zones 5 to 10
- Light
- Full sun, part sun
- Soil
- Average, evenly moist
- Water
- Moderate
- Feeding
- None needed
- Family
- Asteraceae
- Comes from
- Canada, Cuba, southeastern United States, NC
- Attracts
- Pollinators, butterflies, moths, songbirds
- Stands up to
- Deer, wet soil
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.