Invasive Plants: You Can Help, Don’t Plant or Nurture a Pest

by Beth Mather

“Don’t Plant a Pest” is the title of a pamphlet published by the California Invasive Plant Council that discusses issues associated with plants that have been brought to California and which have been found to be harmful to our native habitats. These plants may look good in yards and many people and government entities have planted them over many years. Some have been here so long and have become so widespread that many people think they are native plants.

Unfortunately, we have learned a hard lesson that some of these introduced plants are quite harmful to California native habitats. Those that are harmful, the invasive ones, cause considerable damage not only to California native habitats but also to California agriculture.

The plants that are invasive here in California are not inherently bad. Plants invasive in California are usually good members of their plant communities in their native range because they remain in check. But when they are introduced into California outside that native range, they grow with few checks and balances. Some characteristics of invasive plants are they spread easily; they out compete native plants in a number of ways including competing for space, water, and pollinators; they can change the soil chemistry; they can change the ecology, affecting the animal life in an area. Some also affect the hydrology of an ecosystem by becoming a flood hazard or by using excessive water. They can also be fire hazards.

We have our fair share of invasives plants in our preserves. Considerable effort and expense have been and will need to continue to be devoted to ridding our preserves of these invasive plants to attain and then preserve healthy native habitats for wildlife. You can help in this effort by keeping your landscapes free of invasive plants. Please do not plant invasive plants. If you have invasive plants that have either been planted or have spread on their own into your landscapes, please consider getting rid of them so that they do not spread to the open space preserves. As mentioned above, one of the characteristics that make a plant an invasive plant is that they spread easily. Some produce enormous amounts of seed that can be spread by wind, soil movement, water, and animals (including humans).

Here are a few of the culprits that we have in our Preserves and Open Spaces:

Pampas Grass (Cortaderia selloana)

Pampas Grass (Cortaderia selloana). This is an attractive plant, but it has many bad characteristics in our ecosystems. It spreads rapidly especially in moist areas and forms dense stands that compete with native vegetation. The dead leaves can also be a fire hazard. You will find stands of it all around Los Penasquitos Canyon Preserve. The Friends currently have a project to remove pampas grass from Darkwood Canyon and are considering a larger project to remove pampas grass from the rest of the Penasquitos Preserve.

Fennel (Foeniculum vulgare)

Fennel (Foeniculum vulgare). Fennel is also an attractive plant with a pleasant smell that was probably brought to California as a food plant. Unfortunately, it grows quite happily here and spreads into disturbed areas. It grows rapidly and can out compete native plants for water and sunlight. It is quite pervasive in our area.

Artichoke (Cynara cardunculus)

Artichoke (Cynara cardunculus). This is another food plant that grows without controls here in Southern California. It is a major problem in the Santa Luz grasslands of the Black Mountain Open Space where it has formed a monoculture, but it is also found scattered throughout our other preserves where it continues to spread and out compete other plants.

African Fountain Grass (Pennisetum setaceum)

African Fountain Grass (Pennisetum setaceum). This is one of many non-native grasses that is prevalent around San Diego. It is an attractive perennial grass that has been used as a landscaping plant along roadways as well as in landscapes. It spreads rapidly and has invaded many people’s landscapes. It is very aggressive and outcompetes native plants. Because it grows so dense, it can increase the fuel load and increase the intensity of a fire.

Mexican Feather Grass (Nassella tenuissima)

Mexican Feather Grass (Nassella tenuissima). This is an emerging invasive plant in California and has already been designated an invasive plant in Australia and other places. It is a very popular ornamental grass that has been used extensively in San Diego. According to the UC Master Gardener website, it crowds out native species of grass as well as pasture species. It produces tens of thousands of seeds which are dispersed by wind or water, and the seeds will persist in the soil for years.

Sea Lavender (Limonium sinuatum)

Statice or Sea Lavender (Limonium sinuatum). Although this species Limonium is not listed as an invasive plant on the California Invasive Plant Council List, other species of Limonium are listed and this one is spreading in Penasquitos Canyon as well as other places in the city. It seems to form dense patches to the exclusion of other plants. Despite its lack of officially being designated as invasive, the Los Penasquitos Canyon Preserve rangers want to control its spread.

Canary Island Date Palm (Phoenix canariensis)

Canary Island Date Palm (Phoenix canariensis). These palms, commonly used in landscaping, are invasive in canyons and riparian areas. It is a good idea not to plant these palm trees because they are susceptible to the newly introduced South American Palm weevil.

Mexican Fan Palm (Washingtonia robusta)

Mexican Fan Palm (Washingtonia robusta). This non-native palm grows quickly and reproduces well due in part to the large number of seeds it produces. It can quickly form dense thickets and out competes our native riparian trees as well as other native plants. The dead and untrimmed fronds are also a fire hazard.

This is a very short list of some of the problematic perennial invasive plants in our preserves. There are many others, both perennial and annuals. We encourage you to be aware of what is growing in your yards and around your properties. There are several apps that you can use to identify plants that you aren’t familiar with. Seek or iNaturalist or even the information button on your iPhone photos is good at identifying common plants.

If you do identify invasive plants growing in your landscapes, consider replacing them. There are many non-native plants that are not invasive. But better yet, plant a California native plant. Our native animals tend to do better on native plants because they are better adapted to the native plants. San Diego County is blessed with a wide variety of native plants that can be substituted for the invasive plants. Visit the CalScape website or the California Native Plant Society website’s native plant profiles. Or check out the “Don’t Plant a Pest” pamphlet. Be aware, however, that not all of the suggestions in the pamphlet are native plants.

Fun fact: Some of our native plants, even some of our endangered plants, are invasive in other parts of the world. For example, the spiny rush that you can find in our preserves is considered an invasive plant in Australia.

For more information on invasive plants in San Diego and California:

https://www.asla-sandiego.org/aslasdwp/wp-content/uploads/2014/10/Most_Invasive_Plant_Guide.pdf.

California Invasive Plant Council, www.cal-ipc.org

For more information on landscaping with native plants:

San Diego Chapter of the California Native Plant Society, www.cnpssd.org, info@cnpssd.org, Calscape.org