Mountain bluet
Centaurea montana · Asteraceae
Large, spidery cornflowers of rich blue with reddish centres in late spring, on a sprawling plant with grey-green leaves.
- Size
- 20 in tall, 20 in wide
- Zones
- 3 to 8
- Light
- Full sun to part sun
- Flowers
- Late May to late June
- Pets
- No toxicity recorded
- Job in a bed
- Drift
A bed built around mountain bluet
The planner designed this bed around mountain bluet when this page was made: a 12 × 6 ft (3.7 × 1.8 m) English border in zone 6, full sun. It chose the other plants from the 966 that suit those conditions, and says below why mountain bluet stands where it does.
The plants
- 1 Mountain bluet × 3, blue
- 2 Blue moor grass × 8, purple
- 3 Leadwort × 13, blue
- 4 Wild quinine × 3, white
- 5 Italian bugloss 'Dropmore' × 5, blue
- 6 Fernleaf peony × 1, red
- 7 Ornamental onion 'Purple Sensation' × 4, purple
- 8 Autumn crocus × 7, lavender
Why this plant
- The only daisies. The others are spires, dense clusters, flat plates and others. Shape reads at a distance, where colours blur.
Why here
- At the back. At 20 in it is seen over leadwort (10 in) in front of it, and has nothing behind it to hide.
- A step in the back row. Next to wild quinine (3½ ft) and Italian bugloss 'Dropmore' (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 six weeks. From late May to late June.
- Part of the bed's peak. With fernleaf peony and ornamental onion 'Purple Sensation' in late May: 3 kinds at once. No week has more.
Planned as an English border: 6 of the 6 groups (100%) are drifts, longer along the bed than they are deep. The bed is balanced: the left half carries 50% of the visual weight and the right half 50%. Blue is the colour seen most, on 3 of the 8 kinds grown for their flowers.
The planner's own design check: 11 Excellent, 6 Good. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where mountain bluet goes in a border
At 20 in it belongs in the middle of a bed. In the planner's ten height classes it is medium short (18 to 24 in).
Its job: drift. Planted in a small group of three or five, and repeated further along in the other number.
A splash of true blue between the bulbs and the summer flowers. It flops after flowering: cut the whole plant to the ground and it returns tidy, often with a second flush.
- Blue for the cottage garden in May and June
- Cut flowers
- Filling gaps between later perennials
What to plant with mountain bluet
Plants recorded as good partners for it, and what each pairing does:
- Peony: in flower together for four weeks, from late May; tall enough (3 ft) to stand behind it.
- Lady's mantle: in flower together for five weeks, from late May.
- Oriental poppy: blue against orange, opposite each other on the colour wheel, if you choose those colours, in flower together for five weeks; tall enough (2½ ft) to stand behind it.
Questions about mountain bluet
Does mountain bluet need sun or shade?
Mountain bluet 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 ordinary well-drained soil, of average fertility, and little watering once settled. It copes with soil that stays wet.
What zones does mountain bluet 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 mountain bluet flower in my zone?
In zone 5 it flowers late May to late June. As a spring flower it moves about a week for every zone: earlier where it is warmer, later where it is colder.
| Zone 3 | Early June to early July |
|---|---|
| Zone 4 | Late May to early July |
| Zone 5 | Late May to late June |
| Zone 6 | Mid May to late June |
| Zone 7 | Early May to late June |
| Zone 8 | Early May to late June |
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 mountain bluet be planted?
18 in (45 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 20 in (50 cm), so a group knits into one patch.
It grows 20 in (50 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many mountain bluet plants do I need?
At 18 in apart, set out in staggered rows:
- 5 to fill 10 square feet (about 1 m²)
- 7 for a single row 10 ft (3 m) long
- 17 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 mountain bluet 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.
Is there a native plant like mountain bluet?
Mountain bluet comes from Europe. These North American natives come closest to doing its job:
- Eastern bee balm: the same job in a bed, the same size and the same flowering time; pink, not blue.
- Lanceleaf coreopsis: the same job in a bed, the same size and the same flowering time; yellow, not blue, wants dry soil.
- Wild geranium: the same job in a bed and the same size; flowers early May to late May, pink, not blue.
Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.
Do deer eat mountain bluet?
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 mountain bluet spread?
It spreads sideways, by runners or roots; the risk of it taking over is moderate. Spreads by runners and self-seeds, and has become weedy in parts of the Pacific Northwest. Cut it back hard after flowering.
What flowers after mountain bluet?
Mountain bluet is over by late June. These start as it finishes and carry the same spot on, so it never goes flat:
- Black-eyed Susan: from mid July to mid September, 24 in tall.
- Butterfly weed: from late June to early August, 24 in tall.
- Daylily: from late June to early August, 2½ ft tall.
What does mountain bluet look like in winter?
Mountain bluet 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 mountain bluet good for bees and butterflies?
Mountain bluet is visited by bees and butterflies.
More Centaurea
- Mountain bluet 'Amethyst in Snow' Centaurea montana 'Amethyst in Snow'
- Persian cornflower Centaurea dealbata
In these guides
- Plants for wet soil and rain gardens
- Pet-safe plants for a sunny border
- Plants for butterflies
- Plants for bees
- Plants with blue flowers
- Silver and grey-leaved plants
Zone guides: Zone 3 · Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8
Every fact on record
- Type
- Perennial
- Size
- 20 in (50 cm) tall, 20 in (50 cm) wide
- Plant
- 18 in (45 cm) apart
- Height class
- Medium short (18 to 24 in)
- Place in the bed
- Middle
- Flowers
- Late May to late June; daisies; blue
- Leaves
- Medium texture, herbaceous; grey-green
- Shape
- Mounding, spreading
- Hardy in
- USDA zones 3 to 8
- Light
- Full sun, part sun
- Soil
- Average, well-drained
- Water
- Low
- Feeding
- None needed
- Family
- Asteraceae
- Comes from
- Europe
- Attracts
- Bees, butterflies
- Stands up to
- 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.