Q. What makes a plant invasive, and why are they considered harmful?
Whenever we hear about invasive species, we usually think about pest insects or arthropods such as Argentine ants or fruit flies. Although these are bad enough, invasive plants can have even worse widespread and long-lasting impacts.
A plant is considered invasive if it is non-native and its introduction is likely to harm the native environment or cause economic damage. They are generally fast-growing, spread readily (usually by seeds), adapt easily to a variety of conditions, are tough to kill, and lack any natural enemies.
One invasive plant species, Scotch broom (Cytisus scoparius), can still be found in many big-box home stores and garden centers. This shrub bears bright yellow flowers and is easy to grow. Unfortunately, it can now be found in many wild areas where it has displaced the native plant population. When this happens, the native birds, insects, and other wildlife lose their food sources.
Pampas Grass, thankfully, has fallen out of favor. In the 1990s, it was a popular landscape plant due to its dramatic, towering seed heads and extreme hardiness. Its sawtooth-edged leaves made it a good barrier plant since anyone who tried to climb through it would be cut to shreds. If you tried to remove it, those blades were a major hazard. You could try digging it out, but if any trace of roots remained, the plant would just come back. The seeds dispersed easily and gave rise to hundreds of unwelcome plants. On top of all this, the plant has the unfortunate tendency to explode when exposed to fire. Of course, nothing eats it.
Japanese Bindweed is another difficult-to-eradicate invasive that is a common weed in home landscapes. It winds its way around neighboring plants and can girdle trees if allowed to grow around their trunks. Its aggressive nature results in it undermining sidewalks and other concrete structures.
Many invasives are herbicide-resistant due to their deep and extensive root structures (or just plain orneriness). If they invade farmland, they can choke out crops.
Southern California’s climate is like the environment in many parts of Asia, South America, and Africa. It’s warm with mild, frost-free winters and has an abundance of well-irrigated land. We also have many international travelers and busy ports. These conditions make California the ideal place for invasive species to thrive.
It’s important to at least not contribute to the problem, and there are several things you can do. If you travel internationally, please don’t bring back any plant material, including seeds or seed-containing fruit. Don’t buy or plant invasives, even if they’re on sale at the local big-box store. For a list of invasive plants (and some native substitutes), see PlantRight – Promoting noninvasive plants for California.
Los Angeles County
mglosangeleshelpline@ucdavis.edu; 626-586-1988; celosangeles.ucanr.edu/UC_Master_Gardener_Program/
Orange County
ucceocmghotline@ucanr.edu; mgorange.ucanr.edu/
Riverside County
anrmgriverside@ucanr.edu; 951-955-0170; ucanr.edu/sites/RiversideMG/
San Bernardino County
mgsanbern@ucanr.edu; 909-387-2182; mgsb.ucanr.edu
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