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French broom - Genista monespessulana- click for larger image
French broom is a European species originally introduced as an ornamental to North America.  It is well-adapted to our climate of dry summers and mild winters and is capable of invading beyond where it is planted and out-competing other plant species.  Already a widespread problem in northern California and on the move in Oregon, French broom has the potential to threaten grassland habitats and out-compete forage species in Washington and to become a serious pest plant. French broom closely resembles other broom species including two other noxious weeds, Scotch broom and Spanish broom. The only currently known escaped population of French broom in King County is on the south campus of the University of Washington near the Montlake Bridge.

Legal status in King County, Washington

Public and private landowners are required by state law to eradicate this plant when it occurs on their property. French broom is a Class A Noxious Weed in Washington due to its limited distribution in the state and the potential for significant impact to state resources. It was added to the state list in 2013. It is on the King County list of Regulated Class A Noxious Weeds. For more information see Noxious Weed Lists and Laws

Identification
French broom - Genista monspessulana - infestation - click for larger image

  • Large tap-rooted shrub with yellow, pea-type flowers and small oval leaves in groups of three
  • Older stems are brown and more or less round; younger stems are green, ridged and very leafy
  • Leaves and young stems covered with silvery hairs
  • Flowers are small and in clusters of 4-10 on ends of small branchlets
  • Seeds are in small brown pods, 0.4 to 1.2 inches (1-3 cm) long, covered with silky, silvery to reddish gold hairs
  • Can be distinguished from Scotch broom by its brown stems, leaves always in threes (some Scotch broom leaves are single), smaller flowers, and seed pods entirely covered by hairs (Scotch broom pods are only hairy on the edges)

Habitat and impact

French broom - Genista monspessulana by Montlake Cut - click for larger image
French broom is well-adapted to open, sunny, well-drained sites and is mostly likely to negatively impact open habitats.  Tolerant of summer drought and low-nutrient soils, French broom can invade a wide range of habitats including roadsides, fields, logged areas, bluffs and coastal areas. Similar to Scotch broom, French broom can fix nitrogen through its association with soil fungi and thereby disrupt low-nutrient ecosystems such as Puget Sound prairies.  French broom can also interfere with re-forestation and can aid the spread of wildfires. High seed production and long-lived seeds make eradication of established populations very difficult.

Growth and reproduction

French broom is a woody, tap-rooted shrub that reproduces by seed.  It doesn't spread vegetatively from its roots, but plants can survive cutting and tend to re-sprout from the crown when cut or burned.  Seeds are produced in hard, dry legume pods that burst open when mature.  Seeds are generally dispersed close to the parent plant unless soil is moved through erosion, flooding or other means. Similar to other broom species, French broom seeds are hard and long-lived.  Plants can produce over 8000 seeds a year.

Control

French broom - Genista monspessulana plant - click for larger image
Prevention: French broom may still be offered for sale, possibly under a different common name, so take care to avoid purchasing this species by checking the Latin name of any broom plants you purchase.  Keep an eye out for new broom seedlings in areas near existing populations and make sure to remove them while they are still young and before they go to seed.  After removing, mulch area thickly to prevent seed germination and re-plants with site-appropriate species that will shade out any future seedlings.

Small patches: Plants can be hand-pulled when young or mechanically pulled with a weed wrench or similar tool when larger.  Look for seedlings wherever plants have gone to seed in past years.

Larger patches: This plant can generally be controlled with the same methods as for Scotch broom.  If applying herbicide, the best timing is when plants are most actively growing in the spring or early summer, before the dry season.  On the other hand, cutting plants is most effective during the dry season, usually from late July to mid-September in this area.  Please refer to herbicide labels for site specific control information and refer to the PNW Weed Management Handbook for additional information on herbicide use.

Additional information on French broom

What to do if you find this plant in King County, Washington

Please notify us if you see French broom growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. Also, because French broom is not generally established in King County, we have an opportunity to stop it from spreading if we act quickly. We map all known locations of regulated noxious weeds such as flowering-rush in order to help us and others locate new infestations in time to control them.

Report French broom in King County, Washington

Locate French broom in King County, Washington

Related information

Related agencies


Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact staff, see the Noxious Weed Control Program Directory, send an email, or call 206-477-WEED (206-477-9333).