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

5-119. Rather than leaving applicants to check the state list on their own, the city code names four species outright as specifically prohibited: Chinese and Siberian elms, cotton-bearing cottonwoods, meaning female Populus species that produce the wind-borne cotton, Russian olive, and box elder. All four are common Front Range trees that spread aggressively, crowd out native riparian vegetation, or, in the case of cottonwood, create a seasonal cotton nuisance, which is likely why the city singled them out rather than relying only on the general state list cross-reference.

B, which also requires species diversity, no more than 5 percent of any single species and no more than 20 percent of any single plant family on a lot, and directs species selection toward those suited to the local climate as promulgated by the Colorado State University Extension. The section was last amended by Ordinance No. 20, Series of 2023, and Ordinance No. 10, Series of 2025, effective June 12, 2025.