Sweet broom, encompassing species like Genista monspessulana and Cytisus scoparius, is a plant frequently encountered in various landscapes. This shrub often appears along roadsides and in disturbed areas. While it offers certain aesthetic and functional attributes, sweet broom also presents notable environmental concerns.
Identifying Sweet Broom
Sweet broom typically grows as an upright shrub, reaching heights of 6 to 8 feet and spreads of 5 to 6 feet. Its branches often have a gentle, arching lean. The leaves are usually trifoliate, meaning they have three leaflets, and maintain a bright to medium green color. Younger stems are often slender, multi-stemmed, and can appear five-angled.
The most distinctive feature of sweet broom is its profusion of bright yellow, pea-like flowers. These fragrant blooms typically cluster along the stems. Flowering can occur from late winter and early spring through mid-summer. This plant has a rapid growth rate and adaptability, tolerating conditions including wind, poor soil, drought, and rocky areas.
Using Sweet Broom in Your Landscape
Sweet broom has historically been used in landscapes for various functional and aesthetic purposes. Its robust root system makes it suitable for stabilizing soil on hillsides and controlling erosion. This characteristic led to its widespread planting along highways and in other disturbed sites.
The plant’s fast growth and dense habit allowed it to serve as a quick-growing screen or hedge. It can provide a visual barrier, and its vibrant spring blossoms add striking color. Its hardiness and ability to thrive in challenging conditions, including drought tolerance once established, contributed to its popularity.
Caring for Sweet Broom
The plant thrives in full sun exposure and requires well-drained soil. While it tolerates poor and rocky soil conditions, some species may prefer an alkaline soil pH.
Watering needs are most pronounced during the first year after planting to ensure a deep root system develops. Once established, sweet broom is drought tolerant, but it benefits from supplemental irrigation during extended dry, hot periods. Fertilization is minimal; a single annual application of a balanced fertilizer in spring before blooming is often sufficient. Avoiding high-nitrogen fertilizers is advisable as they can promote leaf production over flowers. Pruning sweet broom yearly in late spring or summer, after the blooming period, helps maintain its shape. Pruning about one-third of the plant’s older wood encourages healthier growth.
Understanding Sweet Broom’s Environmental Impact
Despite its landscape uses, sweet broom poses significant environmental risks due to its invasive nature. Both Genista monspessulana (French broom) and Cytisus scoparius (Scotch broom) are aggressive invaders that form dense, impenetrable stands. These thickets outcompete and displace native vegetation, reducing local biodiversity. Many regions, including parts of California and Australia, list these species as controlled or noxious weeds.
As members of the legume family, sweet broom species fix nitrogen in the soil. This alters soil chemistry, increasing nutrient levels which can disadvantage native plants adapted to low-nitrogen environments. The formation of monocultures by sweet broom can degrade natural ecosystems such as grasslands, forests, and rangelands.
Sweet broom’s high flammability is a concern. The plant contains oils and resins that ignite easily and burn intensely. Its dense growth habit contributes to increased fuel loads and creates “ladder fuels,” allowing fires to spread rapidly from the ground into the tree canopy. During dry seasons, the plant’s foliage and seed pods dry out, exacerbating fire risks.
Control and removal are challenging due to its prolific seed production. Seeds can remain viable for up to 60 years. They are explosively dispersed from pods, and the plant can resprout from its root crown, making eradication difficult.
Sustainable Alternatives
For vibrant yellow flowers and a shrub form, consider planting Forsythia, Yellow Azalea (Rhododendron luteum), Shrubby Cinquefoil (Dasiphora fruticosa), or Japanese Kerria (Kerria japonica). These provide yellow flowers and shrubby growth without invasive tendencies.
For erosion control on slopes, native shrubs such as Shrubby St. John’s Wort (Hypericum prolificum) and Spicebush (Lindera benzoin) have strong root systems. Diervilla, like the Kodiak Orange variety, also spreads effectively through suckering roots for erosion prevention. Native grasses such as Inland Sea Oats, Little Bluestem, or Prairie Dropseed are excellent for soil stabilization.
For effective screening or hedging, non-invasive choices include ‘Green Giant’ Thuja (Arborvitae), ‘Chindo’ Viburnum, or English Laurel (Prunus laurocerasus). These alternatives provide similar landscape benefits while promoting ecological health.