Photo by Melody

PlantFiles: Mountain Bluets, Quaker Ladies, Azure Bluet
Houstonia caerulea

Family: Rubiaceae
Genus: Houstonia (hoos-TOH-nee-uh) (Info)
Species: caerulea (see-ROO-lee-uh) (Info)

Synonym:Hedyotis caerulea
Synonym:Houstonia caerulea var. faxonorum

13 members have or want this plant for trade.

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Alpines and Rock Gardens

under 6 in. (15 cm)

6-9 in. (15-22 cm)

USDA Zone 3a: to -39.9 C (-40 F)
USDA Zone 3b: to -37.2 C (-35 F)
USDA Zone 4a: to -34.4 C (-30 F)
USDA Zone 4b: to -31.6 C (-25 F)
USDA Zone 5a: to -28.8 C (-20 F)
USDA Zone 5b: to -26.1 C (-15 F)
USDA Zone 6a: to -23.3 C (-10 F)
USDA Zone 6b: to -20.5 C (-5 F)
USDA Zone 7a: to -17.7 C (0 F)
USDA Zone 7b: to -14.9 C (5 F)
USDA Zone 8a: to -12.2 C (10 F)
USDA Zone 8b: to -9.4 C (15 F)

Sun Exposure:
Sun to Partial Shade


Bloom Color:
Light Blue
White/Near White

Bloom Time:
Late Spring/Early Summer
Mid Summer
Late Summer/Early Fall


Other details:
Average Water Needs; Water regularly; do not overwater

Soil pH requirements:
5.6 to 6.0 (acidic)
6.1 to 6.5 (mildly acidic)

Patent Information:

Propagation Methods:
By dividing the rootball
Direct sow as soon as the ground can be worked

Seed Collecting:
Collect seedhead/pod when flowers fade; allow to dry

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3 positives
1 neutral
No negatives

Gardeners' Notes:

Positive coriaceous On Apr 17, 2014, coriaceous from ROSLINDALE, MA wrote:

A lovely native plant here. I've found populations varying tremendously in size and color. The blues vary from mid-blue to nearly white, and in the same population I've found individuals that are pure white (with the yellow throat). In New England, I mostly see pale skim-milk colored flowers, and near Washington DC I mostly see them in a more saturated sky blue.

They seem to occur naturally where there's little competition, generally in small patches on acid, infertile soils in thin grass, usually accompanied by moss. I see them growing in full sun to dappled shade, often in very dry places under trees, and in the grassy verges of highways. I can't imagine that they'd survive in a dense thriving lawn, and I can't imagine them growing as a weed-suppressing ground cover. The individual plants themselves are smaller than a fingernail, and the flowers are huge relative to the size of the plant.

Whenever I've transplanted them into a flower bed, I've lost them. But they've grown well and sown themselves in the pure sand between walkway pavers, where they look splendid.

Here in New England, they bloom for a couple of weeks in May, well after most daffodils are finished. Near Washington DC, they bloom in the latter half of April.

"Bluets" or "azure bluet" means Houstonia coerulea.
"Mountain bluets" means Centaurea montana.

Positive _emily_rose On Apr 16, 2014, _emily_rose from Chattanooga , TN (Zone 7b) wrote:

I love my Bluets! They appeared in the mossy areas of my lawn the first spring in my house, two years ago. They like moist shady areas, but are starting to spread out, moving to some of the sunnier and grassier areas. What started as a dotting of color in my yard the first spring is turning into a carpet of color. They begin to bloom with the first daffodils. Because of my shade, I rarely cut my grass, and I think this has helped them naturalize.

Neutral Mainer On Jan 23, 2008, Mainer from Durham, ME (Zone 3a) wrote:

These grow wild in our fruit orchards, fields, pastures here in Maine.

Positive lego_brickster On Sep 12, 2004, lego_brickster from Lawrenceville, PA (Zone 5b) wrote:

These are native to our area (Zone 5), and one of the few flowers that came with the house.

They seem to thrive in the shady, damp and acidic lawn which is otherwise covered only with moss, but we have spotted them in much drier and nearly full sun locations.

We look forward to these every spring, and bloom at the same time as daffodils and other spring flowers. They can last for weeks. It is a fine sight to see your lawn awash in sky-blue flowers!
By the time the lawn starts growing, these have all but disappeared.

We don't know much yet about their propagation. We started this year by simply dividing and transplanting a clump. The flowers are so small that I have not found a seed yet. We'd love to grow more.


This plant has been said to grow in the following regions:

Louisville, Kentucky
Durham, Maine
Oakland, Maryland
Billerica, Massachusetts
North Billerica, Massachusetts
Norton, Massachusetts
Roslindale, Massachusetts
Greenville, New Hampshire
Croton On Hudson, New York
Elizabethtown, New York
Keeseville, New York
Saugerties, New York
Raleigh, North Carolina
South Point, Ohio
Cranberry Twp, Pennsylvania
Lawrenceville, Pennsylvania
Milford, Pennsylvania
Millersburg, Pennsylvania
Wilkes Barre, Pennsylvania
Chattanooga, Tennessee
Leesburg, Virginia
Roanoke, Virginia

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