Invasive plants in California: How to identify and control them

Q: My neighbor planted periwinkle as a ground cover and it is coming under the fence into my yard and taking over my shrub beds. How do I get rid of this pesky plant?

A: I feel your pain; I have been waging a 20-year battle with periwinkle, aka vinca major, in my own yard. It was the main ground cover around the house when we moved in, and I have not been successful in completely removing it as it grows under shrubs and trees I want to keep. It propagates itself from rhizomes (underground stem runners) and by rooting the stems above ground at each node. It comes up through thick mulch and if left unchecked, it can completely smother small shrubs and any annual or perennial plantings.

My way of keeping the vinca in check it to cut it back to the ground with a string trimmer a couple of times per year and to pull any of the plants that start to move out of the area where it is ground cover. Herbicides will kill it but you may need several applications, spread out over a few weeks, to completely eradicate it. Because the source of the vinca is not coming from your yard you will have to stay vigilant and remove or spray any new plants that emerge on your side of the fence.

Vinca major is listed as a highly invasive plant in California. The University of California Statewide Integrated Pest Management Site defines Invasive plants in the following way. "The important biological difference between invasive plants and garden or agricultural weeds is the ability of invasive plants to disperse, establish, and spread without human assistance or disturbance. Because of this, they are much more problematic in natural environments than are typical weeds." Due to their ability to spread so easily, invasive plants cause ecological disruption to our natural environments, choking out native plants, altering water availability and in many cases increasing fire danger. According to the U.S. Forest Service, "Invasive species have contributed to the decline of 42% of U.S. endangered and threatened species, and for 18% of U.S. endangered or threatened species, invasives are the main cause of their decline."

Over 60% of all invasive plants in California were intentionally introduced for use as a landscape plant, a fish aquarium plant, medicinal plant or for livestock feed. Some of the worst invasive trees were purposely introduced. For example, the tree of heaven, a very invasive tree, was brought to the United States in the late 1700s as a horticultural shade tree. Another invasive tree, the Chinese tallow tree, is said to have been introduced in the country by Ben Franklin, so the seeds could be used in soap and candle making. The blue gum eucalyptus was introduced to serve as a wood source during the Gold Rush in areas that had few trees, it has now choked out swaths of native ecosystems around the Bay Area and the Central Coast.

The best way to avoid planting a plant that will cause problems later is to educate yourself on what plants to avoid. The California Master Gardeners have worked with the Plant Right organization to survey nurseries and educate nursery owners on the invasiveness of certain plants. Plant Right is a nonprofit organization that works to educate nursery and landscape professionals on what plants to avoid selling and planting and to provide alternative non-invasive choices for the landscape. To see the list of California invasive plants, and some of the non-invasive alternatives to these plants, check out the Plant Right plant list at https://plantright.org/about-invasive-plants/plant-list/

For a more extensive list of landscape plants that are invasive, or have the potential to become invasive, check out the "Plants in Horticulture List" at the non-profit organization Cal-IPC website https://www.cal-ipc.org/

The Shasta Master Gardeners Program can be reached by phone at 530-242-2219 or email [email protected]. The gardener office is staffed by volunteers trained by the University of California to answer gardeners' questions using information based on scientific research.