Broom and Gorse Identification and Removal
There are several members of the legume plant family (Fabaceae) that are invasive and problematic throughout Mendocino County. Weedy brooms (French, Scotch, and Spanish) and common gorse are extremely invasive, outcompeting native plants and increasing the risk of fire.
Why are brooms and gorse a problem?
Brooms and gorse were introduced to California as ornamentals in the 1800s and by the early 1900s had escaped cultivation and became invasive. These long-lived perennial plants form a deep, branching taproot that is difficult to remove once established. They produce copious amount of seed that can remain viable in the soil for at least 30 years, with some estimates of up to 80 years. These seeds are impenetrable to water and can be dispersed long distances by water flowing in storm drains and streams, as well as by insects, animals, and humans. The seeds can withstand a wide range of temperatures and moisture levels, and are stimulated to germinate following soil disturbance or fire. Cutting and mowing is not effective in controlling brooms and gorse as they readily resprout from the root system.
Brooms and gorse form large, dense clusters of vegetation that sprawl outward from the center of the plant. The center of mature plants is woody, containing dead vegetation that is extremely dry and flammable. Gorse is especially problematic as the foliage and stems contain volatile oils which are highly flammable. The town of Bandon, Oregon is known to have burned several times due to being inundated with gorse.
Detrimental to native plants and livestock
As members of the legume family, brooms and gorse are nitrogen-fixing, which allows them to thrive in nutrient poor soils. These plants quickly colonize disturbed areas along roadsides, construction sites, and near communities. Once established, these plants outcompete and shade out native plants, reducing the overall plant cover and increasing the potential of soil erosion. Gorse leaf litter acidifies soil making it difficult for native plants to reestablish themselves in close proximity to gorse. Brooms and gorse plants are unpalatable and potentially toxic to livestock, except goats, making them a major concern for ranchers and farmers.
How to identify brooms and gorse
There are three invasive brooms (French, Scotch, and Spanish) found within Mendocino County and one more (Portuguese) that is known to be in Sonoma County. As members of the same plant family (Fabaceae) they share similar characteristics, with Scotch and Portuguese brooms often being mistaken for one another. See the diagnostic features for each of these plants below.
French broom (Genista monspessulana)
French broom is a perennial, woody, evergreen shrub that can reach up to 10’ tall. It has bright yellow pea-like flowers that bloom from March to May, forming ¼” – 1 ¼” long, hairy, pea-like seedpods. Common along roadways, disturbed sites, and habitat edges throughout Mendocino County.
Size: 3’ – 10’ tall, up to 10’ wide
Stem: ridged with fine hairs
Foliage: abundant leaflets of 1-3 (usually 3), each less than 1” long, evergreen
Flowers: bright yellow pea-like flowers, 4-10 per cluster, blooms March – May
Fruit: pea-like seedpods ¼” – 1 ¼” long, hairy, brown, and slightly flattened when mature
Scotch broom (Cytisus scoparius)
Scotch broom is a perennial, woody, deciduous shrub that can reach up to 8’ tall. It has bright yellow to red pea-like flowers that bloom from March to May, forming ¾” – 2” long pea-like seedpods with hairy margins. Common along roadways, disturbed sites, and habitat edges throughout Mendocino County.
Size: 4 – 8’ tall, up to 10’ wide
Stem: 5-angled (star-shaped in cross-section), glabrous
Foliage: sparse leaflets of 1-3, each less than 1” long, deciduous
Flowers: bright yellow to red pea-like flowers, 1-2 per cluster, blooms March – May
Fruit: pea-like seedpods ¾” – 2” long, darkened when mature, hairy only on margins
Spanish broom (Spartium junceum)
Spanish broom is a perennial, woody, deciduous shrub that can grow up to 10’ tall. It has bright yellow pea-like flowers that bloom from April to June, forming 1 ½” – 4” long pea-like seedpods with fine, silver hairs. Found along roadways, disturbed sites, and habitat edges in southern Mendocino County.
Size: up to 10’ tall and wide
Stem: cylindrical and glabrous (rush-like)
Foliage: sparse and small, each less than 1” long, deciduous
Flowers: bright yellow pea-like flowers, several per cluster, blooms April – June
Fruit: pea-like seedpods 1 ½” – 4” long, slightly flattened, covered in fine silver hairs
Portuguese broom (Cytisus striatus)
Portuguese broom is a perennial, woody, deciduous shrub that can grow up to 9’ tall. It has bright yellow pea-like flowers that bloom from May to August, forming plump pea-like seedpods covered in hair. Found along coastal scrubs, grasslands, and disturbed sites. It has not yet been found in Mendocino County, but is known to be in Sonoma County.
Size: 6’ – 9’ tall, up to 10’ wide
Stem: slender, with 8 – 10 ribs, appears round in cross-section
Foliage: sparse leaflets of 1-3, each less than 1” long, deciduous
Flowers: bright yellow pea-like flowers, 1-2 per cluster, blooms May – August
Fruit: pea-like seedpods are plump and densely covered in fine hairs
Gorse (Ulex europaeus)
Common gorse is a perennial, woody, evergreen shrub that can grow up to 10’ tall. It has bright yellow, pea-like flowers that bloom from April to July, forming hairy ½” – 1” pea-like seedpods. Gorse is distinct from brooms as it has a dense covering of singular, spine-like leaves. Gorse contains volatile oils that are highly flammable, making it concerning in fire-prone areas. Found along the Mendocino Coast, especially in the Caspar region.
Size: up to 10’ tall and 30’ wide
Stem: hairy stems with ½” spines at the base of leaves
Foliage: singular leaflets, approximately ½” long, stiff or spiny, evergreen
Flowers: bright yellow pea-like flowers, 1-2 per cluster, blooms April – July
Fruit: densely hairy pea-like seedpods ½” – 1” long
Control methods for brooms and gorse
Brooms and gorse colonize new areas rapidly and once established, are extremely difficult to remove. Restoration efforts for removing populations of brooms and gorse have had limited success and require years of monitoring and follow-up treatment. An integrated management approach, incorporating a variety of control methods and years of follow-up monitoring and treatment, has the best chance of success.
- Prevention. Prevention is the most important defense against broom and gorse invasion. These plants should never be intentionally planted outside their native habitats (none of these weedy brooms or gorse are native to the United States). Care should be taken to avoid transporting seeds to non-infected areas.
- Immediate removal of new populations. Any new stands of broom or gorse should be removed immediately before they fully establish themselves and begin seed production.
- Mowing/Grazing. Smaller plants can be mowed with machinery or grazed by goats (brooms and gorse are unpalatable and potentially toxic to other grazing livestock) before they become too large and woody. Mowing and grazing does not remove the roots of the plants and they will resprout from the remaining root system. This method will need to be repeated annually and can help keep small populations from going to seed. Mowing and grazing can also be a follow-up method to control resprouts that emerge following other control methods. These methods are not selective and may result in damage to native plants that are also in the area to be treated.
- Digging/Pulling. Larger plants can be dug or pulled out using a weed wrench. This is more effective than mowing as it removes much of the root system and reduces, but does not eliminate, the chance of resprouting. Digging and pulling plant roots disturbs the soil which can stimulate broom and gorse seeds in the seed bank to sprout, potentially increasing the local population of these plants. Digging and pulling may be most effective in the late summer, when plants are experiencing water stress. This method is laborious and only practical for small areas or if there is a large pool of volunteers or inexpensive labor available.
- Cutting/Sawing. Larger plants that cannot be dug or pulled out, can be cut or sawed. Cuts should be made at or below the soil surface to reduce the chance of resprouting. Plants should be cut before they produce seeds and follow-up control (mowing, grazing, fire, or herbicides) should be used on future resprouted vegetation. Shredding the stump with an axe may decrease the likelihood of the plant resprouting. Like digging, cutting may be more effective if done during dry months when the plants are experiencing water stress.
- Heavy Equipment. Heavy equipment, such as bulldozers, backhoes, excavators, and brush hogs, can be used to remove dense thickets of broom and gorse. This should not be used in sensitive areas where native species are of concern. Follow-up control (mowing, grazing, fire, or herbicides) should be used on future resprouted vegetation. Care should be taken to ensure seeds are not transported on the equipment to off-site locations.
- Herbicides. Herbicides can be effective in controlling brooms and gorse. Great care should be taken to avoid non-target species. Direct, manual application of herbicide to invasive plants is the most effective means to accomplish this, but it is laborious. Treating large areas with herbicides may result in standing dead biomass that could increase local fire risk.
- Mulching. Applying a 3 – 4” layer of mulch or straw (certified weed-free) may inhibit broom and gorse seeds from sprouting. This method can be expensive and time consuming, and may not be practical in large areas.
- Fire. Controlled burning may be used to suppress large infestations of brooms and gorse. Controlled burns must be conducted during the rainy season, which is well after the plants have gone to seed. Fire may stimulate broom and gorse seeds in the seed bank to germinate, potentially increasing the local population of these plants after the fire. Burned plants may also resprout from the root system and follow-up control methods should be used on resprouted vegetation and seedlings.
- Biological. There are a number of insects that feed on brooms and gorse. Several have been used with limited success. Biological control is highly variable as control agents are often not plant specific and are not confined to the target area.
- Steam treatment. High temperature steam may be applied to soil to destroy seeds near the soil surface. This method can be used to reduce the seed bank in large areas. Steam treatments are not target-specific and can be expensive.
- Cultural. Establishing native plants can prevent the establishment of non-native, invasive species. As soon as possible, native plants should be reintroduced to burned areas and sites where invasive plants have been removed. This is a crucial follow-up control that is often overlooked.
- Follow-up. The control methods listed above are most effective when used in combination with one another. Following the initial removal of the invasive species, annual monitoring and follow-up treatment should occur annually for at least five years. Native plants should be reintroduced to the site immediately and their success monitored as well.