San Mateo County, CA Landscaping Rules: Weed Ordinances (2026)

San Mateo County does not have a single county-wide grass-height ordinance for occupied lawns; hazardous-vegetation control on vacant and open land is administered by the fire protection districts serving the unincorporated area, using the County's authority to abate fire-hazard weeds and rubbish under Health & Safety Code 14875 et seq., Government Code 25845, and Penal Code 370 et seq. The Coastside Fire Protection District's Weed and Rubbish Abatement Program (covering coastside unincorporated areas and Half Moon Bay) states that 'weed abatement shall be accomplished by mowing weeds and grasses to a height of no taller than four inches.' Combustible grass, weeds, trash and rubbish must be removed from vacant lots, yards, courtyards and parkways. Unimproved properties of one acre or less must be cleared in their entirety (except wetlands and riparian areas); properties larger than one acre must have a fire break 'not less than 30 feet in width around the perimeter.' To protect sensitive habitat, there is no mowing within a wetland or within a 100-foot buffer around a wetland, and fire breaks must stay at least 50 feet from riparian (streamside) vegetation. Importantly, the City of Half Moon Bay and the County of San Mateo 'no longer allow disking as a method of vegetation removal.' Defensible space under PRC 4291 (see Grass Height) overlaps these requirements for structures.