The Kenwood Press
News: 04/01/2019

Pull out the French broom

It may be pretty, but itís also an invasive weed and fire hazard



french broom
Photo by Forest and Kim Starr

Every spring, you can drive or walk around and see a pretty, tall, leafy shrub with bright yellow flowers. But itís really not pretty at all.

Despite its good looks, French broom is not your friend; itís a weedy intruder threatening native plant species. And you can find it all over Sonoma Valley, Sonoma County, the North Coast, the Bay Area, and other parts of the state, covering an estimated 100,000 acres.

Drive around northern Sonoma Valley Ė you canít miss it.

The story goes that French broom (Genista monspessulana) was brought over to California in the mid- to late-1800s from the Mediterranean area of Europe as an easy-to-grow ornamental plant. It soon escaped the confines of personal gardens and is now one of the most damaging invasive plant species in California.

French broom is highly aggressive and out-competes native plants and displaces them, and can dominate native flora with its thick stands that can get up to 10 feet high.

A member of the pea family, French broom can alter the soil makeup by increasing the level of nitrogen in the ground, which encourages other non-native weeds to grow.

French broom apparently isnít very tasty either (the flowers and seeds can be toxic), so the wildlife wonít eat it, and their normal diet can be affected because the pervasive shrub is taking the place of edible plants.

And, the oils in French broom makes it easily combustible, thus increasing fire hazards.

French broom has its most rapid vegetative growth from April to July, and becomes reproductive at two to three years of age, if not sooner.

French broom spreads so easily because the seed pods open explosively and throw an amazing number of seeds as far as three to four meters.

According to the California Invasive Plant Council, a medium sized shrub can produce over 8,000 seeds a year, and seeds can survive at least five years in the soil and often much longer, thanks in part to a hard coating that covers the seed.

How do you get rid of French broom? Itís hard to get rid of it entirely because it reseeds so easily, but the most effective eradication method is to use your hands. Conservation groups across the state have been involved for years in organizing work parties to remove French broom.

It is not good to cut it because it comes back stronger and the roots get harder to pull.

To effectively fight French broom, you need to have a strategy after the initial removal because of the bushís prodigious seedbank.

This is a great time to pull out the French broom when the earth is soft and the roots will let go easily. Itís also easy to see when itís blooming and really important that it doesnít go to seed. Removal sites should be looked at once a year in order to get rid of new seedlings, and this should be done for five to 10 years.

For more information on French broom go to the California Invasive Plant Councilís website at www.cal-ipc.org.