8 Invasive Plants in the Bay Area & Some Beneficial Native Alternatives

Vegetation is an important and beautiful part of our local natural places, but what happens when some plants take over? Below, you’ll find the stories of eight destructive species you’ll surely recognize, along with some beneficial native alternatives.

You’ll also learn more about local volunteer efforts, where community members are joining forces to keep aggressive invasive plants under control. The best part is: you can help too! When we roll up our sleeves at Bair Island and pull out crown daisy, we’re not just tidying up the wetland and trails. We’re giving our local plant life a chance to thrive.

Let’s get digging!

WHY DO NATIVE PLANTS MATTER IN THE BAY AREA?

California’s 6,500 native species are generally forces for good. They have been in our region all along, feeding and sheltering local critters and keeping our ecosystem in tip-top shape.

By contrast, invasive plants can wreak havoc, hogging resources and squeezing out our most necessary resident species. Unfortunately, as Bay Area plant enthusiasts can attest, much of the greenery we see daily is invasive. Luckily, there are ways for locals to make a difference, by volunteering to be land stewards or being mindful of the seeds they plant in their yards.

BE A STEWARD FOR BIODIVERSITY

If you’re eager to pitch in on local land stewardship efforts, there are plenty of opportunities nearby.

Where to Volunteer

Skip ahead to find ways to volunteer with POST, Grassroots Ecology, San Francisco Bay Bird Observatory, Keep Coyote Creek Beautiful, and other Bay Area organizations.

NATURE’S TROUBLEMAKERS:

BLACK MUSTARD (Brassica nigra )

This fast-growing plant fills fields in California’s coastal grasslands and abandoned lots every springtime. The cheerful yellow expanses that result have inspired many road trip photos. Wild mustard’s four-petaled flowers are the same sunny-yellow hue as the condiment.

HOW IT GOT HERE

Your history teacher might have once schooled you on wild mustard’s colonial roots. A few centuries ago, Franciscans scattered their seeds along the El Camino Real to make the road between missions more visible. Researchers have traced the trail of invasive mustard by analyzing seeds and pollen found in the Mission era’s adobe bricks. 

WHY IT’S TROUBLESOME

• Black mustard suppresses native plants’ growth, which diminishes habitat and food sources for local pollinators. 
• It outcompetes native plants by germinating early and leeching toxic chemicals into the soil.
• In the dry season, it creates dangerous wildfire fuel. Native plants, by contrast, have often adapted to fiery conditions.

NATIVE ALTERNATIVES

Give it up for local (and equally photogenic!) wildflowers!

 

JUBATA GRASS (Cortaderia jubata )

Atop durable stalks, this plant’s tall, showy plumes mimic ostrich feathers. It looks almost identical to pampas grass (Cortaderia selloana), the feathery (also invasive!) plant in many suburban gardens. Despite the similar appearance, this common coastal weed is actually a separate species.  That said – we wouldn’t recommend either for your garden!

HOW IT GOT HERE

Native to Bolivia, Ecuador, Peru, and Chile, this Andean plume grass may have entered the horticulture world via France. It is unclear how or when it landed in California. In 1966, it popped up as a weed in Humboldt County’s logged redwood forests.

WHY IT’S TROUBLESOME

• Each plume produces up to 100,000 seeds (yikes!). Once wind disperses them far and wide, they rapidly colonize bare ground. As such, this plant is incredibly tough to eradicate. You’ll find it in dunes, bluffs, coastal shrublands and marshes, and inland riparian areas.
• Due to its sharp, silica-filled leaves, pampas grass is trecherous for large mammals, like us, to navigate through. This is particularly true when they fill new or eroding trails and begin to colonize the open space.

NATIVE ALTERNATIVES

Get a load of these California native grasses.

 

ICEPLANT (Carpobrotus edulis )

Known for its colorful flowers, this fast-growing succulent litters San Francisco’s Presidio area. But it doesn’t stop there! Its lush, fleshy leaves abound in many coastal habitats from north of Eureka to Baja.

HOW IT GOT HERE

Native to South Africa, iceplant is a coastal succulent shrub. It first appeared in California in the early 1900s as a potential tool to stabilize erosion on railroad tracks and roadsides. 

WHY IT’S TROUBLESOME

• Once established, this coastal invader forms a large, thick mat. This prevents the sand’s natural movements, which many native dune species need to survive.
• It alters the soil composition, making it more acidic and less rich in calcium, magnesium, and other minerals, choking out endangered, threatened, and rare native plants.
• Despite their reputation for erosion control, iceplants can cause landslides on steep slopes! This is because they become weightier after significant rainfall.

NATIVE ALTERNATIVES

Sift through other plants that like sandy soil.

 

SOUR GRASS (Oxalis pes-caprae )

Chances are you gnawed on the lemony stems of this common garden weed during childhood. It crops up in urban areas like highway medians, empty lots and sidewalk cracks. Because it spreads so rapidly, locals can now spy sour grass in remote locations, too, from coastal dunes to oak woodlands to orchards and agricultural areas.

HOW IT GOT HERE

Native to South Africa, where it is rare and endangered, sour grass has become a pest plant in Mediterranean climates worldwide.

WHY IT’S TROUBLESOME

• Hardy and aggressive, it crowds out native wildflowers for light and space.
• It spreads quickly without seeds. Instead, it has a thin underground stem bearing many small bulblets. Even if you tear out the stems, any bulblets left behind can still flourish.

NATIVE ALTERNATIVES

Fill your garden and your plate with several edible native plants.

 

EUCALYPTUS (Eucalyptus globulus )

Prominent on the California coast, Tasmanian blue gum eucalyptus smells medicinal — like a topical vapor rub. These tall stands of trees feature long, tapered leaves and shaggy bark. They prosper even in poor soil.

HOW IT GOT HERE

During the Gold Rush, Australian prospectors brought seeds to California. Wood was then a powerful resource, necessary for firewood, energy and building up new cities. However, the settlers would find that blue gum, which is prone to splitting and cracking when grown outside of Australia, was a poor option for woodworking.  

WHY IT’S TROUBLESOME

• The bark and leaves they shed contain chemicals that stunt the growth of other plants.
• Their dead leaves and oily shaggy bark offer abundant fuel for wildfire, and their height can carry flames into the canopy.

NATIVE ALTERNATIVES

Grow your appreciation for California urban oaks!

 

FRENCH BROOM (Genista monspessulana )

French broom is the most widespread of North America’s four invasive broom species. Producing over 8,000 seeds per plant annually, it currently occupies around 100,000 acres in California alone. You’ll find it on coastal plains, mountain slopes, river banks, roadsides, and forest openings. It can also take over grassland and open-canopy forest.

HOW IT GOT HERE

French broom came to the San Francisco Bay Area in the mid-1800s as an ornamental. It is native to countries in and around the Mediterranean and the Azores Islands.

WHY IT’S TROUBLESOME

• Unpalatable or toxic as a food source for most livestock, it decreases rangeland value while increasing fire hazards.
• It burns readily and provides ladder fuels that can carry fire to the forest canopy layer. This can increase both the frequency and severity of fires.

NATIVE ALTERNATIVES

Bask in some sun-loving native shrubs.

 

TREE OF HEAVEN (Ailanthus altissima )

Never mind the virtuous name: this tree is truly a devil in disguise. When crushed, its leaves emit a foul odor, reeking of rancid peanut butter. Its stinker status distinguishes it from lookalike native trees. Another telltale feature is its samara fruits, aka “helicopter seeds”—single seeds encased in a papery wing.

HOW IT GOT HERE

Brought to the US from China, this deciduous tree became a shade source for cities in the late 1700s. Resilient to pollution, drought, insects, and plant disease, it is thought to be the fastest-growing tree in North America.

WHY IT’S TROUBLESOME

• Due to its abundant seeds, it crowds native species with dense thickets. It also secretes a chemical into the soil that is toxic to nearby plants.
• Its aggressive root system can damage human structures like pavements, sewers, and building foundations.
• It hosts the invasive spotted lanternfly when the insect lays eggs there.

NATIVE ALTERNATIVES

Behold the stately California black walnut!

 

OLD MAN’S BEARD (Clematis vitalba)

With creamy white flowers and oval leaves, this invasive climbing vine favors forests and woodlands. Left unchecked, it forms dense, gnarled mats on the ground. (Read how we worked with partners and contractors to remove this destructive plant in POST-protected San Vicente Redwoods!)

HOW IT GOT HERE

Native to Europe, Asia, and Africa, Old Man’s Beard came from early European settlers. They may have brought it over purposefully to adorn gardens or by accident via contaminated soil or seeds carried on ships.  It looks very similar to native clematis species, and well-intentioned habitat restorationists have accidentally spread this species through revegetation efforts.

WHY IT’S TROUBLESOME

• Old Man’s Beard wraps its tendrils around tree trunks. Next, it climbs to hoard sunlight, often choking trees and native ground plants.
• When it takes over as ground cover, it creates a monocrop (i.e., a single crop that grows year after year on the same land) unsuitable for most native species. This significantly harms native insects that survive on diverse vegetation and form a critical link in the food chain.

NATIVE ALTERNATIVES

Get wrapped up in vines with habitat value!

WHERE TO VOLUNTEER

POST hosts monthly volunteer events with a variety of partners that could use some help thinning out invasives, planting native species, and identifying the organisms in a habitat. 

POST is far from being alone on our volunteer mission. Many of our great partners host their own extensive volunteer opportunities that provide even more ways to help out on the land. We highly encourage you to look into volunteering with any of these environmental protection organizations: 

• Grassroots Ecology
• San Francisco Bay Bird Observatory
• Keep Coyote Creek Beautiful 
• Santa Clara County Parks
• San Mateo County Parks
• Surfrider Foundation
• Midpeninsula Open Space District
• Santa Clara Valley Open Space Authority 
• Veggielution
• Save the Bay
• Environmental Volunteers
• Amah Mutsun Tribal Band

Having a hand in improving your local landscape is very rewarding, and fortunately, very easy to do in the Bay Area. By getting out on the land to remove invasive plants, we help our region’s native species to thrive. Now that you know more about invasives and their native alternatives, you can put your knowledge to use for the benefit of the land, including your community garden or backyard!