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Soft broom identification and control
About this weed
French broom is a regulated Class A noxious weed. This means eradication is required state-wide. French broom is also on the Washington quarantine list and it is illegal to buy, sell or offer it for sale in the state.French broom is known as Genista monspessulana and it is in the pea family.
Why it’s a problem
French broom is well-adapted to our climate of dry summers and mild winters. It is capable of spreading beyond where it is planted and out-competing other plant species.
French broom can fix nitrogen, meaning it can take nitrogen from the air and add new nutrients to the surrounding soils. This can negatively impact low-nutrient ecosystems such as Puget Sound prairies.
French broom is highly flammable. It can aid the spread of wildfires. High seed production and long-lived seeds make eradication of established populations very difficult.
It is already a widespread problem in northern California and it is on the move in Oregon. French broom has the potential to impact grasslands and other open areas in Washington.
Plant description
French broom is a European species originally introduced as an ornamental to North America. French broom is well-adapted to open, sunny, well-drained sites. It is tolerant of dry summers and low-nutrient soils. It can grow in a wide range of habitats including roadsides, fields, logged areas, bluffs and coastal areas.
French broom is a large tap-rooted shrub with yellow, pea-type flowers and small oval leaves in groups of three.
The weed's older stems are brown and more or less round. Younger stems are green, ridged and very leafy.
The leaves and young stems are covered with silvery hairs.
Flowers are small and in clusters of 4-10 on ends of small branchlets.
The seeds are in small brown pods, 0.4 to 1.2 inches (1-3 cm) long, covered with silky, silvery to reddish gold hairs.
Be aware of look-alike plants
French broom is similar to other broom species. These include two other noxious weeds, Scotch broom and Spanish broom.
Some key identifiers of French broom are its brown stems and its leaves are always in threes. It has smaller flowers and its seed pods are entirely covered by hairs. Scotch broom, in comparison, has green stems, single leaves, larger flowers, and its pods are only hairy around the edges. Another difference between the two brooms is the outer envelope (calyx) around the flower is different. French broom's has 5 pointed teeth and Scotch broom's has two rounded lips.
A great resource to distinguish several broom species can be found at UC IPM Brooms.
When in doubt, take photos and share them with us or report them on iNaturalist.
What to do if you find it
Property owners are required to control French broom on lands that they manage. Please notify us if you see French broom growing in King County.
Our program staff can provide you 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.
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.
Control methods
We recommend using a combination of methods to control noxious weeds. In areas with few weeds, it is important to act quickly before they become harder to control. Make a long-term plan as it often takes several years to get rid of most weeds. Start in the least infested areas first and then move into more heavily infested areas.
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. Weed wrenches and other tools can be borrowed from Tool Libraries in the region.
Larger patches
Stay safe when using herbicide:
- Always read the label before use.
- Wear a long-sleeved shirt, long pants, shoes, and eye protection.
- Follow state and local regulations.
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. The dry season is from late July to mid-September in Western Washington.
See the PNW Pest Management Handbook for the most up to date and specific method for chemical control of French broom.
Disposal instructions
Do not put plants with seed pods in compost or yard waste. Seeds are very tough and long‐lived and can contaminate mulch made from compost. Ideally, control activities should be done before plants go to seed to avoid disposal problems. For small amounts, dispose of entire plant with seed pods in the garbage.
Plants without seeds can also be disposed of with household or municipal yard waste.
If it is not practical to dispose of the broom as recommended above, leave plants with mature seed pods on‐site to limit spread to new areas.
Noxious Weed Disposal - Washington State Noxious Weed Control Board