St. Louis County, MO Invasive Plant Rules: Prohibited Species (2026)

Chapter 620, the Managed Natural Landscapes Code, lets an owner "install and maintain a managed natural landscape" on qualifying property under Section 620.110, and Section 620.115(b) confirms that landscape "may include plants and grasses in excess of eight (8) inches in height and which have gone to seed, but may not include any noxious weeds or nuisance or invasive plants, and must be maintained so as to not include unintended vegetation." Section 620.115(c) repeats the species ban in stronger language: a managed natural landscape "may not include any noxious weeds, nuisance or invasive plants, or any other plantings, which due to location and manner of growth, constitute a hazard to the public or may cause injury or damage to persons or property." Section 620.005 pulls its definitions straight from the county's Weed Control Code at Section 619.005, where an "invasive plant" is "a vegetation species that grows aggressively in the State of Missouri, as listed by the Missouri Department of Conservation," a "noxious weed" is "a vegetation species that is listed as a Missouri State Noxious Weed by the United States Department of Agriculture," and a "nuisance plant" covers toxic species such as poison hemlock, poison ivy and ragweed.

Chapter 620 applies, like the Weed Control Code, to non-vacant property with a recorded subdivision plat and land within 100 feet of such a subdivision's boundary, outside incorporated cities, towns and villages, per Section 620.010. Managed natural landscapes must also stay authorized by the owner, avoid blocking sight distance for traffic, and sit at least 5 feet from a neighboring property line unless a sight-proof fence separates them, per Section 620.115(a), (e) and (f).