Mountain Bluet

Mountain Bluet (Centaurea montana)

Report

Management Strategy

Synonyms

Perennial Cornflower

ID Characteristics

General: Mountain Bluet is a long-lasting perennial herb that grows from 30 – 80 cm tall.

Flowers: Delicate compound disk flowers, 5 – 8 cm wide, with blue ray petals and black-fringed bracts on the base of each flower. Flowers contain both male and female organs. This species can re-bloom in late summer or early fall.

Stem: Multiple, erect, upright, unbranched and slightly hairy.

Leaves: Lanced-shaped to egg-shaped, with a woolly underside. Leaves are 10 – 30 cm long and arranged alternately along the stem.

Seeds: Seeds are light yellow to golden, glossy and about 5 mm long, with a short pappus (cluster of hairs).

Roots:Mountain Bluet has a taproot and creeping rhizomes.

Similar Species

Native:

Blue Thimble Flower (or Globe Gilia, Gilia capitata) is a plant that is native to BC and is often confused with Mountain Bluet. However, its flowers are more spherical than Mountain Bluet’s.

Blue Thimble Flower (or Globe Gilia) is native to BC.

Non-native:

Bachelor’s Button (Centaurea cyanus) is also invasive. Its foliage is finer and it doesn’t have spreading rhizomes.

Bachelor’s Button is another invasive, blue-flowering plant in the Sea to Sky.

Habitat and Origin

Mountain Bluet was brought over from Europe as a medicinal plant. It is now used widely as a garden ornamental.

Mountain Bluet is hardy and drought-tolerant, growing well in most soil types and climates. This species prefers full sun to partial shade and moist but well-drained soils. Mountain Bluet is most commonly found in meadows, pastures, ditches and disturbed areas. As a garden escapee, it often escapes to adjacent areas.

How it Spreads

Mountain Bluet reproduces by seed as well as vegetatively, via rhizomes. It is self-seeding: the flowers contain both male and female organs, so they can self-pollinate. The seeds can remain viable in the soil for several years.

Seeds may be spread by livestock, farm equipment, vehicles, and humans. Mountain Bluet also spread through the horticulture trade, since it is sold as an ornamental. Lastly, Mountain Bluet can spread through the improper disposal of garden waste.

Impacts

Ecological:

Colonizes quickly, and can grow into thick stands, displacing native plants.
Can alter native plant-pollinator interactions and reduce forage opportunities for wildlife and livestock.

Economic:

Outcompetes forage species.
Can lead to decreased food sources for livestock.

Stop the Spread

There is insufficient information about Mountain Bluet’s distribution, impacts, potential for spread and feasibility for control in the Sea to Sky. If you see Mountain Bluet, please report it.

Learn to identify Mountain Bluet: use the images presented on this profile page to learn how to identify Mountain Bluet.

What to do if you spot it: You can report any Mountain Bluet sighting by visiting our reporting page.

DO:

Regularly monitor properties for weed infestations.
Ensure soil and gravel are uncontaminated before transport.
Check wildflower mixes to ensure that they do not contain Mountain Bluet.
Ensure that plants are disposed of in a garbage bag if found in floral arrangements to prevent seeds from spreading.

DO NOT:

Do not purchase or trade Mountain Bluet.
Unload, park or store equipment or vehicles in infested areas; remove plant material from any equipment, vehicles or clothing used in such areas and wash equipment and vehicles at designated cleaning sites before leaving infested areas.
Plant Mountain Bluet in a garden, no matter how well-contained its enclosure may seem.
Move soil that has been contaminated with Mountain Bluet.

Control

Mechanical

Repeated hand-pulling, ensuring the root system has been removed, is the most effective way to control infestations of Mountain Bluet.
Repeated cutting or mowing before plants set seed each year can also be effective, however any roots left intact can re-sprout.
If the infestation is well established, there is likely a seed bank, so repeated mechanical removals will need to occur until all seeds have germinated or expired.

Chemical

Effective herbicides include dicamba, 2,4-D, clopyralid, aminopyralid, and glyphosate.
Picloram is also effective, but not appropriate to use in coastal, moist soils.
Herbicides can be applied using wick-on or selective spot-spraying to minimize non-target damage.

We recommend that any herbicide application is carried out by a person holding a valid BC Pesticide Applicator Certificate. Before selecting and applying herbicides, you must review and follow herbicide labels and application rates; municipal, regional, provincial and federal laws and regulations; species-specific treatment recommendations and site-specific goals and objectives.

Biological

No biocontrol agents are currently available for Mountain Bluet.

Sea to Sky Distribution

Note: Mountain Bluet is more common than the map below suggests. SSISC crews are actively adding observations to our database, and we are asking people to report locations of this species, so its distribution can be better understood.