Invasive Plants of Southern California

Biodiversity is the backbone of healthy, resilient ecosystems. California is uniquely biodiverse, with a wide range of plant and animal species found nowhere else in the world. Stewarding biologically diverse natural systems provides immense benefit to our environment, economy, and community.

When invasive plants establish themselves in new habitats, they displace native flora and fauna, causing biodiversity loss. They can heighten the area’s susceptibility to wildfires, floods, and landslides. This increased vulnerability to natural disasters leads to significant costs and endangers the wellbeing of humans and the ecosystem.

This page provides information on common invasive plants of Southern California that form dense stands that outcompete native plants and increase the risk of wildfire.

Jump to:

Common Invasive Plants
Glossary
Additional Resources

Invasive Plants of Southern California

Jump to:

Common Invasive Plants
Glossary
Additional Resources

Biodiversity is the backbone of healthy, resilient ecosystems. California is uniquely biodiverse, with a wide range of plant and animal species found nowhere else in the world. Stewarding biologically diverse natural systems provides immense benefit to our environment, economy, and community.

When invasive plants establish themselves in new habitats, they displace native flora and fauna, causing biodiversity loss. They can heighten the area’s susceptibility to wildfires, floods, and landslides. This increased vulnerability to natural disasters leads to significant costs and endangers the wellbeing of humans and the ecosystem.

This page provides information on common invasive plants of Southern California that form dense stands that outcompete native plants and increase the risk of wildfire.​

How Invasive Plants Spread

Invasive plants spread into natural areas through various means, including: 

  • Disturbance and grading 
  • Planting invasive ornamental plants 
  • Grazing and agriculture 
  • Vehicles and heavy machinery 
  • On your shoes or pets 
  • Contaminated soil and landscape products 

Many invasive plants propagate from seed though some spread via underground roots.   

Stop the Spread

Learn to identify the common invasive plants and determine if they are on your property.

Clean your clothes, shoes, and pets before visiting wild spaces.

Remove invasive plants. Mechanical removal involves using hand and power tools, while chemical methods (herbicide) are generally considered a last resort. Be careful to prevent erosion when removing plants from hillsides.

Help restore biodiversity by choosing native plants for your garden and take steps to prevent the spread of invasive species. Visit your local native plant nursery or botanic garden to learn more.

Together, we can preserve the natural beauty and health of our environment for generations to come.

How Invasive Plants Spread

Invasive plants spread into natural areas through various means, including: 

  • Disturbance and grading 
  • Planting invasive ornamental plants 
  • Grazing and agriculture 
  • Vehicles and heavy machinery 
  • On your shoes or pets 
  • Contaminated soil and landscape products 

Many invasive plants propagate from seed though some spread via underground roots.   

Stop the Spread

Learn to identify the common invasive plants and determine if they are on your property.

Clean your clothes, shoes, and pets before visiting wild spaces.

Remove invasive plants. Mechanical removal involves using hand and power tools, while chemical methods (herbicide) are generally considered a last resort. Be careful to prevent erosion when removing plants from hillsides.

Help restore biodiversity by choosing native plants for your garden and take steps to prevent the spread of invasive species. Visit your local native plant nursery or botanic garden to learn more.

Together, we can preserve the natural beauty and health of our environment for generations to come.

Common Invasive Plants 


Tree of Heaven
Ailanthus altissima

Establishing quickly, small seedlings are commonly found on residential properties and public green spaces. Remove early before they become difficult to pull. Their rapid growth and easy establishment crowds and shades sun-loving native plants. 


Crofton Weed
Ageratina adenophora

If this plant appears in moist areas of your garden remove it quickly. Once sold as an ornamental, it has escaped cultivation and is prevalent in canyons and waterways.


Giant Reed Grass
Arundo donax

A scourge in the waterways of California, it displaces natives at an alarming pace and creates wildfire vulnerability where it did not previously exist.

Brome Grass
Bromus spp.

These fast-igniting grasses can be found in abundance on untended hillsides. To avoid a fast-moving ground fire, string trimming to below 4” is recommended.

 

Pictured: Bromus rubens


Ice Plant
Carpobrotus edulis, C. chilensis

Iceplant is a commonly used succulent which excludes natives and develops a large amount of dry “thatch, which is fuel for wildfire. Its shallow roots create erosion problems.

Pictured: Carpobrotus edulis


Fountain Grass
Cenchrus setaceus and cultivars

A prime example of flashy fuel; it ignites easily, recovers quickly from fire, and can dominate a grassland in 2-3 years. It is frequently seen on hillsides while traveling on local freeways. Synonym: Pennisetum setaceum


Star-Thistles
Centaurea solstitialis, C. melitensis

Star-thistle occupies disturbed and open areas. One plant can produce 75,000 seeds and provide an abundance of flashy fuel. 

Pictured: Yellow Star-Thistle (Centaurea solstitialis)

Pampas and Jubata grass
Cortaderia selloana, C. jubata

These tall, fluffy-headed, fast-growing grasses crowd out lower-growing natives and become wildfire hazards. Pampas grass is especially problematic in coastal areas. “Sterile” cultivars have been observed to selfseed and should not be used. 

Pictured: Pampas Grass (Cortaderia selloana)

Ivy
Hedera canariensis, H. helix, and H. hibernica

Algerian, English, and Irish ivies spread quickly by runners and will travel under or over fences to escape your yard. They can smother trees and large shrubs, creating large masses of ignitable plant material and “fire ladders”. 

Pictured: Canary Island Ivy (Hedera canariensis)


Tree Tobacco
Nicotiana glauca

This tall, adaptable plant will grow easily in Chaparral and Riparian areas. Seen along roadsides and disturbed areas; spreads by rhizomes and seeds; it’s an early sprouter after wildfire. 


Mustard
Rhamphospermum nigrum, Hirschfeldia incana, Brassica tournefortii

Black mustard and shortpod mustard thrive in disturbed areas forming dense monocultures. They can change soil chemistry and create long-lived seed banks. Once dry, mustard creates large amounts of flammable material.

Pictured: Black Mustard (Rhamphospermum nigrum)


Castor Bean
Ricinus communis

A tall, largeleaved plant that will shade out mid-sized natives. Castor bean is a fastgrowing, profuse re-seeder that germinates quickly after wildfire. All parts of this plant are highly toxic. 


Spanish Broom
Spartium junceum

It’s attractive and highly invasive. Originally used as a garden ornamental and for slope stabilization, it develops lots of dry material that is an ignition hazard.

Tamarisk
Tamarix parviflora, T. ramosissima

This tall ornamental tree affects native plant communities by changing the soil chemistry through salt excretion. Generating large amounts of dead and dry material, this plant increases fire risk and recovers quickly post-fire. 

Pictured: Smallflower Tamarisk (Tamarix parviflora)

Periwinkle
Vinca major

A fastgrowing, adaptable invasive with the ability to form a dense groundcover that smothers smaller native plants. Vinca will easily make the jump from your garden to a wild space. 

Common Invasive Plants 


Tree of Heaven
Ailanthus altissima

Establishing quickly, small seedlings are commonly found on residential properties and public green spaces. Remove early before they become difficult to pull. Their rapid growth and easy establishment crowds and shades sun-loving native plants. 


Crofton Weed
Ageratina adenophora

If this plant appears in moist areas of your garden remove it quickly. Once sold as an ornamental, it has escaped cultivation and is prevalent in canyons and waterways.


Giant Reed Grass
Arundo donax

A scourge in the waterways of California, it displaces natives at an alarming pace and creates wildfire vulnerability where it did not previously exist.

Brome Grass
Bromus spp.

These fast-igniting grasses can be found in abundance on untended hillsides. To avoid a fast-moving ground fire, string trimming to below 4” is recommended.

Pictured: Bromus rubens


Ice Plant
Carpobrotus edulis, C. chilensis

Iceplant is a commonly used succulent which excludes natives and develops a large amount of dry “thatch, which is fuel for wildfire. Its shallow roots create erosion problems.

Pictured: Carpobrotus edulis


Fountain Grass
Cenchrus setaceus and cultivars

A prime example of flashy fuel; it ignites easily, recovers quickly from fire, and can dominate a grassland in 2-3 years. It is frequently seen on hillsides while traveling on local freeways. Synonym: Pennisetum setaceum


Star-Thistles
Centaurea solstitialis, C. melitensis

Star-thistle occupies disturbed and open areas. One plant can produce 75,000 seeds and provide an abundance of flashy fuel. 

Pictured: Yellow Star-Thistle (Centaurea solstitialis)

Pampas and Jubata grass
Cortaderia selloana, C. jubata

These tall, fluffy-headed, fast-growing grasses crowd out lower-growing natives and become wildfire hazards. Pampas grass is especially problematic in coastal areas. “Sterile” cultivars have been observed to selfseed and should not be used. 

Pictured: Pampas Grass (Cortaderia selloana)

Ivy
Hedera canariensis, H. helix, and H. hibernica

Algerian, English, and Irish ivies spread quickly by runners and will travel under or over fences to escape your yard. They can smother trees and large shrubs, creating large masses of ignitable plant material and “fire ladders”. 

Pictured: Canary Island Ivy (Hedera canariensis)


Tree Tobacco
Nicotiana glauca

This tall, adaptable plant will grow easily in Chaparral and Riparian areas. Seen along roadsides and disturbed areas; spreads by rhizomes and seeds; it’s an early sprouter after wildfire. 


Mustard
Rhamphospermum nigrum, Hirschfeldia incana, Brassica tournefortii

Black mustard and shortpod mustard thrive in disturbed areas forming dense monocultures. They can change soil chemistry and create long-lived seed banks. Once dry, mustard creates large amounts of flammable material.

Pictured: Black Mustard (Rhamphospermum nigrum)


Castor Bean
Ricinus communis

A tall, largeleaved plant that will shade out mid-sized natives. Castor bean is a fastgrowing, profuse re-seeder that germinates quickly after wildfire. All parts of this plant are highly toxic. 


Spanish Broom
Spartium junceum

It’s attractive and highly invasive. Originally used as a garden ornamental and for slope stabilization, it develops lots of dry material that is an ignition hazard.

Tamarisk
Tamarix parviflora, T. ramosissima

This tall ornamental tree affects native plant communities by changing the soil chemistry through salt excretion. Generating large amounts of dead and dry material, this plant increases fire risk and recovers quickly post-fire. 

Pictured: Smallflower Tamarisk (Tamarix parviflora)

Periwinkle
Vinca major

A fastgrowing, adaptable invasive with the ability to form a dense groundcover that smothers smaller native plants. Vinca will easily make the jump from your garden to a wild space. 

Glossary of Wildfire Terms

Terms familiarize yourself with when learning about wildfire, especially in the context of invasive plant species.

C

Crown fire: A fire existing in the canopy of trees and shrubs. This can be transferred from tree to tree to create a fast-moving fire.



D

Direct Flame Contact: Direct proximity to an already ignited material. Through proximity the processes of radiant heat and convection speed a combustible material to the point of ignition.



E

Ember: Used in conjunction with “firebrand” to describe a piece of smoldering material that can ignite a combustible object through contact.

Ember resistant zone: The 5’ perimeter around a structure that is free of ignitable material including; plants; mulch; furniture.

Ember catcher: A well hydrated plant. Usually a thick-leaved large tree or shrub that can help reduce the flow of embers and firebrands to a structure. Coast Live Oaks are a prime example of an “Ember Catcher”. They are adapted to fire through co-evolution and tend to maintain the moisture needed to resist ignition.



F

Firebrand: Airborne embers of various sizes. These can travel miles ahead of a wind-driven wildland fire to areas ahead of the actual fire line. A predominant source of ignition in a wind-driven fire event.

Fire triangle: The three elements required for a fire to exist: Heat; Oxygen and Fuel. The element we have the most control over is fuel. If we remove or reduce the amount of fuel we can eliminate the fire or reduce its ability to spread.

Flashy Fuel: Fine combustible material that ignites easily and burns quickly. Pine needles and dry grasses are a good example of flashy fuel.

Fuel: Any combustible material. Examples include: Plastic and wood furniture; Wood piles; Poorly maintained trees and plants; Leaves and mulch; Window dressings; Plastic gutters; Wooden and plastic fences; Plastic gutters.



I

Ignition source: There are three main sources of ignition in a wildfire: Embers or firebrands; Radiant heat; Direct flame contact.

L

Ladder fuel: Low growing, low hydration fuels that can transfer a fire vertically, eventually resulting in a crown fire.

Lean, clean and green: Apply this concept as you evaluate your property and landscape for fire resilience. Lean…fewer plants. Clean…free of dry or dead material. Green…well hydrated. This is the concept applied to the 5-50’ zone around a structure.



R

Radiant heat: A heat source that can ignite a combustible material without direct contact. Ignited structures are significant emitters of radiant heat.



S

Soffit-enclosed eaves: This reduces the number of attic entry points under the roof line. It also reduces the eddying effect which traps hot gasses and embers under the eaves. Use non-combustible materials for soffiting. https://defensiblespace.org/house/house-upgrade/



T

Thinning zone: The third zone of maintenance surrounding your house. Reducing the density of large tree and shrub coverage by 50% is effective in slowing advancing fire. This outer buffer zone extends from approximately 50-300’ and is generally unirrigated.



W

Wildland fire triangle: The three elements that dictate the movement of fire through our wild spaces: Weather; Topography and Fuel. The factor we have the most control over is fuel; the amount and type. Reduce the amount of fuel and you increase your properties resilience. In Southern California major weather contributors are hot, dry Santa Ana Winds. Topography comes into play when flame lengths are effectively lengthened as they move uphill. Vegetation should be spaced farther apart on slopes reducing the amount of fuel.

Wildland Urban Interface (WUI): The area of transition from wild, unmanaged space to the area of human development. https://theodorepayne.org/wildland-urban-interface/


This program was made possible in part by Edison International.

Illustrations by Edward Lum.