The Invasive Spanish Broom Plant: Identification and Control

Spanish broom (Spartium junceum) is a perennial shrub in the legume family, native to the Mediterranean. It is recognized by its bright, fragrant yellow flowers and slender, rush-like stems. The plant grows to a height of 10 to 15 feet as an evergreen shrub or small tree. It was introduced globally for ornamental use in gardens and for erosion control along roadways.

Invasive Nature and Distribution

Spanish broom is an aggressive invasive species that grows rapidly, tolerates severe drought, and produces a large number of seeds. These seeds create a persistent seed bank in the soil, with germination often triggered by disturbances like fire or soil movement. This resilience allows it to establish itself in a wide variety of habitats and soil types.

The plant spreads over considerable distances when its seed pods burst open, audibly ejecting seeds away from the parent plant. Significant infestations are found in the western United States, particularly California and Oregon, where it was once planted along highways. It is also a declared invader in Australia, South Africa, and nations in South America like Argentina and Peru.

Identifying Spanish Broom

The plant often appears mostly leafless, with photosynthesis carried out by its numerous bright green, cylindrical, and finely ribbed stems. These erect, rush-like stems give the shrub a unique, broom-like appearance.

Its flowers are pea-like, yellow blossoms about one inch long, arranged in loose clusters at the stem tips and known for their strong, sweet fragrance. The seed pods are flat, linear, and covered in silky hairs when young, turning dark brown or black as they mature. Spanish broom is sometimes confused with Scotch broom (Cytisus scoparius), but Scotch broom has more angled stems and retains more of its leaves.

Problems Caused by Infestations

The plant’s stems have a high content of volatile oils, making dense stands extremely flammable and a considerable fire hazard. These thickets can increase the intensity and spread of wildfires. The dense growth also forms impenetrable monocultures that displace native plant species.

This displacement leads to a loss of habitat for local wildlife. As a legume, Spanish broom also fixes atmospheric nitrogen, which alters soil chemistry. This nitrogen enrichment can be detrimental to native ecosystems adapted to low-nitrogen conditions, disrupting natural patterns and the regeneration of indigenous plants.

Control and Removal Methods

Controlling and removing Spanish broom requires persistence due to its resilient nature and long-lasting seed bank. For small or young plants, manual removal can be effective. Seedlings can be hand-pulled when the soil is moist, and tools like a weed wrench are useful for removing plants up to one inch in diameter. The entire root crown must be removed to prevent the plant from resprouting.

For larger shrubs, the “cut-stump” method is employed, which involves cutting the plant near the base and treating the stump with an herbicide to prevent regrowth. Mowing can manage large infestations if timed between flowering and seed pod maturation to stop seed dispersal. Chemical control with herbicides like glyphosate or triclopyr is also effective on actively growing plants. Always follow local regulations and product label instructions when using chemical treatments.

Toxicity Concerns

All parts of the Spanish broom plant, including the flowers, stems, and especially the seeds, are poisonous to humans and many animals. Ingestion poses a health risk to pets like dogs and cats, as well as to livestock like horses. The toxic effects are due to alkaloids, including sparteine.

Symptoms of poisoning can include nausea, dizziness, and more severe effects like cardiac irregularities. These toxic compounds also make the plant unpalatable to most wildlife, contributing to its ability to dominate landscapes. Due to these risks, it is important to handle the plant with care during removal and ensure that children and animals are kept away from it.