San Mateo County, CA Landscaping Rules: Weed Ordinances (2026)
Key Facts
- Weed/grass max height
- 4 inches (mowed)
- Lots <= 1 acre
- Clear entire lot
- Lots > 1 acre
- 30-foot perimeter fire break
- Wetland buffer
- No mowing within 100 ft of wetland
- Disking
- Prohibited by County & Half Moon Bay
- Authority
- H&S Code 14875 et seq.; Gov Code 25845
Summary
Unincorporated San Mateo County abates hazardous fire vegetation through its fire districts under California Health & Safety Code 14875 et seq. and Government Code 25845. Programs such as Coastside Fire's require mowing weeds and grass to no taller than 4 inches; lots of one acre or less are cleared entirely, and larger lots need a 30-foot perimeter fire break.
5004. “Noxious weed” means any species of plant that is, or is liable to be, troublesome, aggressive, intrusive, detrimental, or destructive to agriculture, silviculture, or important native species, and difficult to control or eradicate, which the director, by regulation, designates to be a noxious weed. In determining whether or not a species shall be designated a noxious weed for the purposes of protecting silviculture or important native plant species, the director shall not make that designation if the designation will be detrimental to agriculture. (Amended by Stats. 1992, Ch. 556, Sec. 1. Effective January 1, 1993.) <input type="hidden" name="javax.faces.ViewState" id="j_id1:javax.fac
Full Breakdown
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.
Violations & Fines
Owners who fail to abate after notice can have the vegetation cleared by the district/County, with the cost billed to the owner and, if unpaid, placed as a lien or special assessment on the property tax roll. Disking is prohibited as an abatement method.
Frequently Asked Questions
How short must I cut weeds on a vacant lot?
Can I disk my lot to clear weeds?
Sources & Official References
Other rules in San Mateo County
California rules heatmap·Compare San Mateo County to another location·View the California landscaping rules overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.