by Hilary Mills, ENC Lead Naturalist/Horticulture Manager
It’s California Invasive Species Action Week! Here are some species to avoid when you’re considering a new plant for your yard:
Brazilian pepper tree is slightly more invasive than Peruvian pepper, but it is not a good idea to plant either one. Seeds readily germinate and grow to create dense stands that shade out other vegetation within a few years of introduction, especially in riparian habitats. Seeds are spread by birds, coyotes, and other wild animals.
These ivy species spread vigorously both as a vine and groundcover, choking out trees and completely covering understory vegetation. It can also harbor non-native snails, rats, and other animal species. It can become particularly invasive in riparian habitats and can easily take root from cuttings.
Native to Europe and Western Asia, Russian olive was introduced as an ornamental plant in the early 1900s. Since then, it has readily escaped cultivation. Seeds are spread by birds and other wild animals, and the tree seriously invades riparian areas, displacing native plants, especially cottonwoods and willows.
Native to mountains in Texas, New Mexico, and Mexico, this grass can become invasive outside its native range. It produces tens of thousands of seeds, which can be dispersed by wind, water, contaminated soil, and even automobiles and shoes. The seed bank can persist for over four years, and the grass will crowd out native plant species in all landscapes and plant communities.
Scotch Broom Cytisus scoparius, Spanish broom Spartium junceum, French broom Genista monspessulana, any other non-native brooms, Retama monosperma, Cytisus striatus
Most of these brooms are native to parts of Europe, the Mediterranean, and North Africa. They are sold at most ornamental nurseries and cause vast problems in Orange County and California wildlands, including our Santa Ana mountains. Seedlings grow rapidly, colonizing burned or disturbed areas more quickly than native species, and will create dense thickets up to ten feet tall. It can shade out native tree seedlings and burns readily, increasing both the frequency and intensity of fires. Seeds are shoots are toxic to many animals as well.
Native to southern Europe and northern Africa, Vinca major is sold as an ornamental groundcover. The vine’s stems take root wherever they touch soil, and this plant can easily take root from cuttings. It spreads rapidly in damp or shaded soils and can smother entire native plant communities in coastal and riparian areas.
Pampas grass is native to Argentina, Brazil, and Uruguay, and was brought to California in 1848 for ornamental use and erosion control. It is now heavily invasive, especially in coastal areas of California. Both jubata grass and pampas grass, though not exactly identical, are both invasive and hard to tell apart. Each flower stalk produces thousands of seeds, which are spread by wind. The plant can grow 5-7 feet, is difficult to remove, and creates a fire hazard when the dry leaves, dry bases, and flowering stalks build up. In natural areas, it competes with native vegetation, increases fire hazards, and competes with tree seedlings, slowing their establishment and growth.
Native to Africa and the Middle East, fountain grass is invasive in multiple western US states, and even Hawaii, Fiji, and Australia. It was introduced as an ornamental plant, and its seeds are easily dispersed by vehicles, people, livestock, and wind. Fountain grass is vigorous and adaptable, and quickly outcompetes native species where it is introduced. It is well adapted to fire, and it completely recover to its original density post-fire; many times it can even been shown to increase its density. Many subspecies and cultivars are sold and advertised as sterile, but this is not always true, and many still may produce viable seed.
Native to south African coastal areas, this succulent groundcover forms think, impenetrable mats that compete aggressively with native plant species. Seeds can travel from landscapes to nearby natural areas by small mammals, and pieces of plants can be washed away by rainwater and transferred to natural areas, where they can take root and become established. It is thought to be a good soil stabilizing plant, but truly it is not because of its shallow roots and heavy, water-retaining nature.