What are invasive plants, and how to stop them from spreading

The temperate climate, broad range in elevation and latitude, and rich soils found in California sustain a rich diversity of native plants throughout the state. This same rich environment can support many species of plants from around the world. Some are beautiful and useful, while others become invasive pests. These invasive plants are fierce competitors that threaten California’s native biodiversity and ecosystems. Unfortunately, about 450 plants originally imported for use in ornamental horticulture in California have “jumped the fence.”

In natural landscapes, waterways and recreation areas are impacted by decreased quality of animal habitat and increased risk of wildfires as invasive weeds take over and crowd out native vegetation.

Along with invasive plants of other origins, these escapees create serious environmental problems. Without the natural controls found in their place of origin, invasive weeds move quickly into agricultural areas and wild lands. In the home garden they can become a significant weeding chore, but their infiltration into agricultural and natural areas are a disaster for land stewards and a financial drain for both farmers and consumers. In natural landscapes, waterways and recreation areas are impacted by decreased quality of animal habitat and increased risk of wildfires as invasive weeds take over and crowd out native vegetation. The costs to manage the problem are overwhelming. Invasive weeds are the second greatest threat to biodiversity and ecosystems after human caused habitat destruction.

How you can help stop the spread of invasive plants

CNPS supports control – and where possible – eradication of invasive weeds (click here to view our policy on invasive weeds – PDF 47k). The most important and economical way to control invasive plants is to prevent their introduction (quarantine). While the California Department of Food and Agriculture (CDFA) maintains programs to prevent the introduction of pest plants, it is up to all of us to prevent the introduction and spread of invasive species. Seeds, as well as entire plants must not be brought into the state unless they are in compliance with quarantine regulations.

Early Detection with Rapid Response is the second most important and economical method of controlling invasive plants. “Eliminate them before they spread” is a sound strategy when dealing with invasive plants. You can help by calling your local County Agricultural Commissioner or Weed Management Area if you come across a population of a possible or known invasive plant. Click here to find information on reporting invasive plants.

If you live in the nine county San Francisco Bay Area you can contact the Bay Area Early Detection Network.

You can also help stop the spread of invasive plants by being careful with clothing and equipment that has been worn or used when traveling from one area to another. Vehicles, animals and pets, and clothing can carry invasive plants from here to there. Make sure that any nursery stock you buy (or sell) is free of invasive weeds.

Most of all, remember that many invasive plants begin as ornamental introductions sold in garden centers and nurseries. You can help control the spread of invasive weeds by not purchasing and planting seeds or plants in your own yard that are known to be invasive in the wild. The California Invasive Plant Council (Cal-IPC) “Don’t Plant a Pest Program” website lists commonly used plants that are known invasive species and suggests alternative plants to use in private or public landscapes. Cal-IPC has also helped develop a partnership that includes production nurseries, the UC Cooperative Extension, and CNPS called the California Horticultural Invasives Prevention (Cal-HIP) partnership. This group supports research based efforts to answer questions about suitable cultivars and screen new introductions. Click here to access the Cal-HIP weed prevention website, and click here to access the Cal-IPC website.


The University of California maintains an excellent resource site that can help identify common weeds and provide information on integrated management plans. To access the UC IPM site, click here.

The UC Davis Weed Research and Information provides an extensive resource library as well. Click here to access the UCD WR&I site.

Resources on Integrated Management Strategies

For more information on the management of invasive plants, there are several good websites to provide identification and integrated management strategies.

For help identifying invasive plants and to obtain more information about management plans of invasive weeds in large areas, you can access the CDFA Encycloweedia website by clicking here.

CDFA also has a website with information on Weed Management Areas (WMAs) in California. CNPS Chapters that participate in local WMAs can coordinate weed management efforts with other groups and are eligible to apply for certain weed management grant funding.


Robert Case, East Bay Chapter

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