Scotch Broom

What is Scotch broom?

Scotch broom is a European shrub in the pea family that was planted in American gardens from the mid-1800s and later used for erosion control along highways. It has since overrun huge areas, especially west of the Cascades and the Sierra Nevada. Scotch broom identification is easy in spring, when bright yellow pea flowers cover the shrubs, and still manageable the rest of the year thanks to its green, sharply ridged stems.

Broom causes trouble on several fronts. Dense stands shut out native plants and young trees; it is now the most widespread forest weed in western Oregon, where timberland control alone costs tens of millions of dollars a year. It fixes nitrogen, which shifts the soil in favor of other weeds. Thickets are a serious fire hazard, and the seeds are toxic to livestock. Its hard-coated seeds also build a seed bank that lasts for decades, so new plants keep coming long after the old ones are gone.

Scotch Broom identification: what to look for

Look closely at a young branch. Scotch broom stems are green and sharply five-angled, so a cross-section looks like a star. Then check the flowers and pods, which together separate it from the other weedy brooms.

• Stems: Green, woody and many-branched, with five sharp ridges; young twigs are hairy, older stems smooth. Young stems stay green all year.
• Leaves: Few and small; three leaflets on lower stems, often a single leaf on new twigs; shed in hot, dry weather.
• Flowers: Bright yellow pea-type flowers about 3/4 inch long in the leaf axils, alone or in pairs, sometimes with red or purple markings.
• Pods: Flattened, dark brown to black, with hairs only along the seams; they split open with a pop in summer.
• Seeds: Small, shiny, greenish-brown, with very hard coats.
• Form: Upright, broom-like shrub forming dense stands.

Where it grows in the United States

Scotch broom grows along the Pacific coast from British Columbia to central California and along the Atlantic coast from Nova Scotia to Georgia, with inland populations in Idaho, Montana and Utah and scattered sites in eastern states. It is also in Hawaii. The worst infestations are west of the Cascades in Washington and Oregon and west of the Sierra Nevada in California, where it covers more than 700,000 acres.

It likes mild, maritime climates with wet winters and dry summers, and it struggles in deserts and places with severe cold. Sunny, well-drained, seasonally dry soils suit it best. In the East it usually stays near old plantings and on disturbed ground, because it competes poorly with lush native vegetation there.

Scotch Broom look-alikes

A few plants get mixed up with it:

• French broom (Genista monspessulana): Stems have 8 to 10 ridges and are nearly round, all leaves have three leaflets and stay green year-round, flowers come in clusters of 4 to 10, and pods are covered in long hairs.
• Spanish broom (Spartium junceum): Round, nearly leafless stems with sparse simple leaves, and larger yellow flowers in open clusters at the branch tips.
• Gorse (Ulex europaeus): Also a yellow-flowered pea shrub, but its stems bristle with spines. Scotch broom has none.

How to get rid of Scotch broom

Pulling, digging and mowing: Pull or dig small plants when the soil is moist, in early spring or late fall; lever-style pulling tools make this much easier, and some county weed boards lend them. In hard, dry soil the stem tends to snap and leave a root that resprouts. Larger shrubs can be cut at the base, but timing matters: cut in late summer when plants are drought-stressed, or in late spring after a dry winter, and watch for resprouts. A single mowing does little, since young plants regrow within months, and late-season mowing spreads seed. Burning alone tends to make things worse by clearing competition and triggering seed to sprout. Plan on pulling seedlings for years.

Cultural control matters most, because the right conditions keep it from coming back.

• After removal, plant competitive desirable species and keep soil disturbance to a minimum, since disturbance wakes up buried seed.
• Goats and sheep eat resprouting broom; grazing works on small areas if pressure stays high enough to keep regrowth down.
• Seed-feeding insects and a twig-mining moth are established in the Northwest and reduce seed production, though results vary and they do not eliminate the shrub.
• Remove mature, seed-producing shrubs first; new plants usually don't flower until their second or third year.

Herbicides: Triclopyr and glyphosate, alone or together, are the main herbicides named for broom, and glyphosate is sometimes paired with imazapyr. Foliar sprays go on actively growing plants, usually April through July, and in mild climates late fall and winter sprays can also work. The ester form of triclopyr penetrates broom best, but above about 80°F switch to glyphosate or the amine form to avoid vapor problems. Cut-stump treatment works year-round if herbicide goes on the fresh cut immediately, and basal bark treatment with concentrated triclopyr ester works almost any time. Triclopyr ester, imazapyr and most glyphosate products are not registered for use near water. Use only products labeled for your site, follow the label (it is the law), and retreat as needed for at least a year. If you hire someone to spray, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Keeping it from coming back

Never plant broom, and remove ornamental brooms before they set seed. Clean soil and seed off equipment, vehicles and boots after working in infested areas, and be wary of gravel or fill from broom country.

Because the seed bank lasts decades, watch for seedlings after any disturbance, including logging, road work, fire or pulling plants. Broom does not tolerate shade, so getting trees or dense desirable cover established discourages it.

Questions we get about Scotch broom

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