Thornton, CO Landscaping Rules: Weed Ordinances (2026)

Section 38-444(a) makes it unlawful for a property owner or lessee, including any occupant or person in possession, to let weeds and brush exceed eight inches in height, subject to four carve-outs. In Agricultural Districts, only noxious weeds must be controlled everywhere, while non-noxious weeds need control only within 100 feet of a boundary with another residential or nonresidential district, or along a street right-of-way. In Parks and Open Space Districts, only noxious weeds are regulated at all. On lots larger than five acres, non-noxious weeds need control only within 100 feet of the lot's property line.

Regardless of any of those exceptions, noxious weeds must always stay below eight inches everywhere on the lot. Once the city sends written notice describing the violation, subsection (b) gives the owner or lessee 10 calendar days to correct it. If they do not, subsection (c) lets the city enter the property, perform the corrective work itself, and assess the owner or lessee for the actual cost of the weed and brush control, plus the city's enforcement costs, including inspection, attorney's fees, and court costs, collected under the assessment procedure in § 38-453(b).