Invasive Plants
Invasive Plants and Prevention
By Kim Wilson, UC Master Gardener
Invasive Plants
Non-native weeds or plants that can survive, reproduce, and spread without human intervention.
They cause economic or environmental harm.
They may be introduced accidentally, but more often intentionally for ornamental, food, forage, or medicinal value.
Naturalized Plants
Non-native plants that can survive and reproduce without human intervention.
They are considered invasive only if they spread beyond where introduced and cause economic or environmental harm.
Agricultural or Garden Weeds
Native or non-native plants that require human disturbance (tillage, fertilization, irrigation) to become established and persist.
They may cause economic or environmental harm, including health problems for livestock or increased agricultural expense.
Introduction is often accidental via people, animals, equipment, or seed contamination.
Environmental and Economic Impact of Invasive Plants
The primary reason to avoid planting invasive species is that they can survive and spread without human interference and cause economic and environmental harm.
- Outcompete and displace native plants.
- Loss of native plants → loss of insects that feed on them → loss of animals that feed on insects and depend on native plants for nesting, roosting, and food.
- Increase risk of wildfires and floods.
- Change soil fertility and promote erosion.
- Clog waterways.
- Impact livestock forage, animal and human health, land value, and recreation.
Invasive plants can serve as hosts for invasive insects. Tree of heaven is an invasive tree and the preferred host of adult spotted lanternfly (SLF), an invasive pest from China. SLF is established in the eastern United States and is not currently in California. It is a significant pest of many fruit crops and woody ornamentals.
Invasive Plants and Plant Nurseries
The California Invasive Plant Council (Cal-IPC) Inventory reports that 37% of invasive plants were accidentally introduced, while 63% were intentionally introduced.
Of the intentionally introduced invasives, 80% were obtained from plant nurseries. Although the number of invasive plants sold has decreased, some stores continue to sell invasive species.
Big-box and online retailers selling across large geographic areas may carry plants that are invasive in San Luis Obispo County. Plants from other regions may behave invasively here.
Prevention
Consult reliable resources to determine which plants are invasive locally and avoid planting them.
Avoid transporting invasive seeds, fruits, or root pieces. Clean shoes, camping equipment, vehicle and bike tires. Brush dogs after hiking. Purchase hay and straw locally to reduce seed contamination risk.
Early Detection and Removal
Monitor property regularly. Early detection and prompt removal of small populations are the most effective management strategies.
Remove plants before flowering. If flowers or seed heads are present, avoid dispersing them.
Cut off flowers or seed heads, bag them, and place in the trash. Remove the remainder of the plant and place in the green bin.
If removal is not possible, prune plants to prevent flowering and seed production.
The County of San Luis Obispo Department of Agriculture Weed Management Program conducts countywide surveillance and manages invasive plants through physical removal, herbicides, and biological control using beneficial insects.
Consult the San Luis Obispo County Weed Management Area page on Cal-IPC (listed below) for information on emerging invasive weeds.