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PlantFiles: Diffuse Knapweed, White Knapweed
Centaurea diffusa

 
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Family: Asteraceae (ass-ter-AY-see-ee) (Info)
Genus: Centaurea (sen-TAR-ee-uh) (Info)
Species: diffusa (dy-FEW-sa) (Info)

Synonym:Acosta diffusa

One member has or wants this plant for trade.

Category:
Annuals
Perennials

Height:
12-18 in. (30-45 cm)
18-24 in. (45-60 cm)

Spacing:
9-12 in. (22-30 cm)

Hardiness:
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)
USDA Zone 9a: to -6.6 °C (20 °F)
USDA Zone 9b: to -3.8 °C (25 °F)
USDA Zone 10a: to -1.1 °C (30 °F)

Sun Exposure:
Full Sun

Danger:
Handling plant may cause skin irritation or allergic reaction

Bloom Color:
Rose/Mauve
White/Near White

Bloom Time:
Mid Summer
Late Summer/Early Fall

Foliage:
Herbaceous

Other details:
May be a noxious weed or invasive
Drought-tolerant; suitable for xeriscaping
Average Water Needs; Water regularly; do not overwater

Soil pH requirements:
6.1 to 6.5 (mildly acidic)
6.6 to 7.5 (neutral)

Patent Information:
Unknown - Tell us

Propagation Methods:
From seed; direct sow outdoors in fall

Seed Collecting:
N/A: plant does not set seed, flowers are sterile, or plants will not come true from seed

Click thumbnail
to view:

By kennedyh
Thumbnail #1 of Centaurea diffusa by kennedyh

By kennedyh
Thumbnail #2 of Centaurea diffusa by kennedyh

Profile:

No positives
No neutrals
1 negative

Gardeners' Notes:

RatingAuthorComment
Negative Joan On Apr 1, 2007, Joan from Belfield, ND (Zone 4a) wrote:

This plant is listed on the North Dakota invasive/troublesome list and this information is being distributed in a guide developed by the ND Weed Control Association and other agencies.

Plant Features
Biennial or short-lived perennial, up to 2 feet tall
One or more stems grow out of a basal rosette
Flower bracts spiny (crab-like), stiff, sharp, light to brown colored
Flowers white to rose, sometimes purple
Blooms from July through August
Small stiff hairs give plants a grayish look
Leaves divided into many segments
Long taproot
Plant breaks at ground level and blows with the wind.
Spreads by seed only

Distribution
Documented in a few areas mostly along roadsides.
Grows under most conditions

Interesting Facts
Suppresses growth of other plants by releasing a toxin (allelopathic)
More highly branched than spotted knapweed
Irritates skin
Widespread invasive in western U.S.

Regional...

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

Belfield, North Dakota



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