History & Introduction

Cytisus scoparius or Scotch broom, is a deciduous, leguminous shrub, native to central and western Europe, and northern Africa. It was first introduced to North America on the east coast, and later introduced to California as an ornamental plant. From the 1850’s to the early 1900’s, Scotch broom was often planted in gardens and later utilized for erosion control along highways and fills. Today, it is classified as an invasive species in the eastern and western parts of North America. In LIISMA, Scotch broom is classified as a Tier 2 invasive species, listed for early detection and eradication. 

Identification & Biology

Scotch broom is a perennial shrub that grows on average from 3-10 ft. tall, but can reach to 13 ft. The stems are five-angled and remain green all year. Branches are hairy or pubescent when young, and mature to be without hairs. The small leaves occur in groups of three. Each leaf is oblong and pointed at both ends. During drought, Scotch broom is known to shed its leaves. Scotch broom has bright yellow, pea shaped flowers that bloom from April to June. Each flower is usually located in the space between the stem and the branch. The fruit is a long, green maturing to brownish black pod, with hairs present along its seams. The seeds inside each pod are shiny greenish brown to black in color. Scotch broom reproduces vegetatively and by seed. The seed pods are often known to be explosive, catapulting seeds a distance away from the mother plant. Two adaptations allow the seed to disperse ever farther: one being a hard and tough seed coat that allows the seed to survive rough transport, especially through water, and two being a fleshy structure that is rich in lipids and proteins that attracts ants. The ants are known to carry the seeds back to their nests, creating dense infestations of scotch broom nearby the nests. Scotch brooms may also be dispersed by goats and horses that ingest and digest the seeds, redistributing them shortly thereafter. 

Scotch broom can be confused with French broom (Genista monspessulana), Portuguese broom (Cystisus striatus), and common gorse (Ulex europaeus). All these species occur in similar habitats, but their appearances differ slightly. The French broom has pods with hairs all over and stems that are not ridged or green. The Portuguese broom has paler yellow blossoms and silver seed pods that are densely covered with white hairs. Common gorse also has bright yellow flowers, but it is spiny and has small, hairy seed pods.

Damage & Concern 

Several characteristics contribute to Scotch broom’s success as an invasive plant: (1) although it loses its leaves during dry conditions, the photosynthetic tissue in its stems allows it to grow throughout the year; (2) its roots host nitrogen-fixing bacteria, which helps the plant to establish in nutrient-poor soils; and (3) it produces abundant seeds that remain viable in the soil for up to 30 years. In addition, Scotch broom also forms dense thickets that displace native plants and does not provide good forage for wildlife. Scotch broom is slightly toxic and unpalatable to livestock as well. 

Management & Control

Early Detection and Prevention

Seedlings are likely to appear in fall or spring, mature plants flower mainly from April to June but flowers may appear sporadically throughout the year. Small populations can be pulled or dug, but the site should be monitored for several years for plants growing from root fragments and from the seed bank. After the control is complete, re-vegetate the site with non-invasive vegetation to compete with seedlings, but make sure the re-vegetation plan is compatible with follow-up weed control activities.

Manual Control

When digging or pulling, make sure to remove as much root as possible so the plant will not re-sprout. This method can be highly labor-intensive and to be fully effective all mature plants in the site need to be pulled so that no new seeds are produced. Both methods are significantly easier when soils are moist. Pulling of medium to large plants is much easier with a weed wrench. Pulling disturbs the soil and creates ideal conditions for broom seed germination so sites will need to be carefully monitored for new growth. When removing Scotch broom on slopes or in areas in which it was planted to prevent erosion, take safety precautions as well as follow-up actions to minimize erosion on site after removal. Cutting can be an effective control method for older plants that are no longer green at the base. If cutting, it is best to cut the plants when they are stressed during the summer drought in late July to August. Cut stems as close to the ground as possible. Monitor for regrowth and cut again. The disadvantage of this method is that plants are typically in seed during the late summer. Cutting may spread the seeds around, so try to cut the plants before the seed pods mature. 

Chemical Control

Foliar applications require a thorough wetting of the actively growing plant parts. This is preferred only for smaller plants. The downside to foliar application is the higher chance of non-target plant damage. Basal bark and cut stump application are also effective and preferred for larger plants; these methods are more target-specific and will damage fewer nearby plants. This can be done as an alternative to manual removal where soil disturbance can be a concern. 

Glyphosate (e.g., Aquamaster, Roundup): can effectively control Scotch broom. Apply to actively growing plants in spring. Addition of a surfactant will improve results. Glyphosate is non-selective and will damage grass and other vegetation it comes into contact with. Treatment with glyphosate needs to be combined with effective re-vegetation of the site to prevent broom seedlings from reinfesting the area. Re-treatment the following year is necessary to control late-germinating plants. 

Triclopyr (e.g. Garlon 3A, Garlon 4, Crossbow): apply any time Scotch broom is actively growing. Foliage must be thoroughly wet. With Garlon 3A it is important to use a high volume of water. Will not injure most grasses. Retaining the grass will help reduce the germination of scotch broom seeds in the soil. Garlon 4 and Crossbow can be used for basal bark applications any time of year.

Monitoring & Reporting 

LIISMA is currently monitoring scotch broom as part of our Early Detection and Rapid Response program. As reports of the species are collected, LIISMA is dedicated to delineating and managing any early emerging infestations of the species before they become widespread. Scotch broom is currently a Tier 2 species on Long Island, prioritized for early detection and containment. 

Your reports matter to us– report the species to iMapinvasives or iNaturalist as soon as you detect it!

iNaturalist is an app and website that can help you record your own observations, identify species, collaborate with others, and access the observational data collected by iNaturalist users. Already using iNaturalist? Join a LIISMA iNaturalist Project to have your invasive species observations automatically uploaded to our projects! Here are some of our projects you can join: Invasive Species in Priority Areas, EDRR Species, LIFERS, Tier 1 Invasive Species, and more!

Want to dive deeper? Check out iMapInvasives to map invasive species like a pro!