Common Name:
French broom
Scientific Name:
Genista monspessulana
Code: GEMO2
Group: Dicot
Family: Fabaceae (Pea family)
Growth Habit: Shrub
Duration: Perennial

What does it look like?

French broom, a member of the pea family. is native to the Mediterranean and the Azores Islands. This bushy plant grows from 5 to 8 feet tall. It has many twisted, single, green branches along with small pea-like blooms of a brilliant yellow shade. French broom is distinguished from Scotch broom by its evergreen trifoliolate leaves. Leaflets are largely oval and the central leaflet is largest, about three-quarters of an inch long (LeBlanc 2001).

Many of the broom species appear similar. One distinct difference between French and Scotch broom is in the small three-parted leaves that grow along the branches of French broom, while Scotch broom has green and mainly leafless branches. French broom seeds are a lighter gray color, and tiny hairs give them a fuzzy appearance. Scotch broom seedpods have hairs along the seams only and are darker, almost black.

Where does it grow?

Native to the Mediterranean region, the Azores and Canary Islands, French broom is now abundant in the Pacific Northwest and Northern Canada. Brooms often grow along roadsides or in disturbed soils. French broom does not like shaded areas but will grow aggressively in open areas such as skid trails, clear cuts roadsides, etc.

Is it in our watershed?

French broom grows extensively throughout the Mattole watershed, primarily along major roadsides and pastures between the towns of Petrolia and Whitethorn. It is particularly thick along roadsides on Shenanigan Ridge.

Why is it a problem?

Initially used in erosion control and as a landscaping ornamental, French broom has since escaped gardens and spread extensively through out the Northwest. French broom is the most aggressive of all the brooms and spreads quickly in disturbed or open areas, rapidly displacing the native vegetation (BPB 2000). Once established, French broom forms monospecific stands, which shade out native species AND increase the intensity and frequency of wildfires. Mature broom plants also establish an extensive seed bank, which can remain viable for up to 10 years even after mature plants are gone.

How do you get rid of it?

It is EXTREMELY important to eradicate French broom while infestations remain small. Because of the tenacious roots and long-lasting seedbank, large-scale infestation removal projects are very time-consuming and costly. It is possible to eradicate French broom with persistence and the proper techniques.

Manual control: Pulling up young plants by hand is one of the best control methods in small infestations or retreatment areas. This technique is most effective to destroy brooms up to 1-1/2 meters tall. Plants should be pulled as soon as they are large enough to grasp but before they produce seeds.

Larger French broom plants can be removed using specialized tools, such as the Weed Wrench while hoeing young plants can also be effective. It is important to disturb the soil as little as possible since this can lead to reinvasion. Broom seeds germinate within top few inches of soil, and any soil disturbances can bring long-lived seed to the surface to germinate (LeBlanc, 2001). Also, hand digging the root system of larger broom plants is a successful eradication technique. However, ALL fragments of roots should be removed since even small pieces of root can produce a new plant.

Mechanical Control: Cutting French broom above the base using machinery such as a brush hog is successful at removing the above ground portion of the plant. However, this is not a successful technique when used alone. The root wads left behind must also be removed because they will continue to reproduce new plants.

Habitat Manipulation: Creating heavy shade can be an effective technique to control many species of brooms, but French broom is more shade tolerant than other brooms (Williams, 1981 in Leblanc, 2001). After removal, re-planting native vegetation can out-compete the broom by ultimately shading the site to prevent broom regeneration.

Biological Control: Several potential insect predators are currently under evaluation. None have been officially approved for broom control.

Author:
Unity Peterson, Invasive Plant Program Coordinator, Mattole Restoration Council, Petrolia, CA.

Photographs:
Unity Peterson

References:
BPB, 2000. Blue Planet Biomes.
http://www.blueplanetbiomes.org/french_broom.htm

Leblanc, John W. Getting a Handle on Broom. ANR Publication 8049. University of California Agricultural and Natural Resources. 2001
http://ucce.ucdavis.edu/files/filelibrary/616/9833.pdf