Denver, CO Invasive Plant Rules: Prohibited Species (2026)

Denver enforces invasive plant regulations under the Colorado Noxious Weed Act (CRS 35-5.5). The Colorado Department of Agriculture maintains three categories of noxious weeds. List A species must be eradicated wherever found and include African rue, giant salvinia, and hydrilla. List B species must be managed to stop their spread and include diffuse knapweed, musk thistle, Russian olive, salt cedar (tamarisk), and toadflax. List C species are designated for educational purposes and include common mullein and field bindweed. All landowners in Colorado, including Denver property owners, have a legal duty to manage noxious weeds on their property. Denver Parks and Recreation and Denver Water actively manage invasive species along waterways and in city parks. The Denver metro area has particular issues with Russian olive trees along the South Platte River, puncturevine in urban lots, and thistles in disturbed soils. Property owners who fail to control noxious weeds may face enforcement through the Colorado Department of Agriculture or local weed management districts.