Scotch Broom

Cytisus scoparius

Class B Noxious Weed (Non-designated: Control Recommended)

General

Native to Europe and Africa.
Aggressively spreads to form monocultures, replacing desirable forage grasses and young trees. Scotch broom interferes with re-establishment of conifer seedlings and can result in stand failures of commercial forestry plantings.
Scotch broom infestations can create more frequent and intense wildfires and act as ladder fuels, carrying fire into tree canopies.
Scotch broom has nitrogen-fixing bacteria located on its root nodules. Scotch broom can alter soil nutrient composition and may have allelopathic properties that inhibit native plants, leaving a legacy effect even after plants have been removed.

Identification

Large perennial shrub with evergreen stems and deciduous leaves; ranging in height from 3 to 12 feet tall.
Leaves are alternately arranged, and simple or divided into three leaflets. Leaves are oblong, being widest towards the tip, and pointed at both ends. Leaves are deciduous and appear in early spring (February to March). Leaves may fall off early in the year, leaving bare green stems.
Young stems are dark green with hairs and have five green ridges. Green stems can photosynthesize all year. Mature stems become yellowish-brown, hairless and ridges disappear.
Flowers are yellow, sometimes having orange-red coloring. Flowers are ¾ inch long, have 5 petals (upper lip two-lobed and the lower lip three-lobed), and pea-like in appearance. Bloom in the spring (April to June)
Seed pods turn from a yellowish green color to a dark brown-black color when mature. Seeds are legume-like, flattened with hairy margins. Each pod contains 3 to 12 shiny seeds. When pods are mature, the two halves audibly split apart making a small popping sound; the seeds can propel up to 15 feet from the parent plant.

Photos

Habitat

Grows in a wide variety of habitats, but grows best in dry, well-drained soils in full sun.
More commonly found growing in open areas but can survive in low light conditions.
Found in disturbed areas such as riverbanks, roadsides, forest clear cuts, power line right-of-ways and also in undisturbed habitats such as grasslands, shrub-lands, open canopy forests, prairies, and oak woodlands.

Reproduction and Spread

Reproduces by seed.
Plants generally begin to flower when they are three years old.
Seeds remain viable in soil for over 30 years and in ideal locations as long as 80 years.
Plants can produce an average of 9,650 seeds per year.
Seeds are dispersed by ants, and people transported by footwear, vehicle tires and seed-contaminated gravels.

Control

Because of Scotch broom’s ability to produce high rates of seed that can survive for long periods of time, control efforts must be monitored and repeated for many years.
Control seedling and young plants before they produce seeds. Soil disturbance will result in a flush of seed germination.
Hand pulling and digging up plants is an effective method for small populations, make sure to remove as much root as possible to avoid resprouting. Use a Weed Wrench to remove larger sized plants, many County Weed Control Boards will let you borrow them for free.
Cutting larger sized plants, stems wider than 2 inches, especially when they are drought stressed in late summer to early fall can be effective. Cut stems as close to the ground as possible. Younger green stemmed plants will regrow.
Mowing followed by burning with a weed torch or herbicide application in the fall, are effective options.

Chemical Control

Use herbicide control in combination with other control methods to reduce usage.
Foliar spray is an effective method, best time is in the spring and again in the fall when plants are actively growing. Requires thorough wetting of actively growing plant parts.
Cut stump method, cut stems just above the ground and immediately apply concentrated herbicide to cut surface. Apply herbicide in late summer, early fall or dormant season. Requires more time, but target-specific.
Do not cut or mow for 2 to 3 weeks after herbicide application.
Herbicides containing the following active ingredients are effective on Scotch Broom:
- Glyphosate (Non-selective herbicide)
  - Foliar application 1.5 to 2% solution, apply to actively growing plants in the spring.
- Triclopyr (Selective herbicide)
  - Foliar application 1 to 1.5% solution, apply any time plants are actively growing.
Cultural methods including mulching and covering the soil after control work, will help reduce germination of the seed bank. Combine with replanting of native plant species to provide additional competition against future seedlings. Shade makes broom grow more slowly, competitive plantings will improve long term control.
Do not put plants with seed pods in compost or yard waste. If plants have seeds, pile and leave on site to avoid spreading infestation. Burning is also an option, follow county burn guidelines.