San Mateo County, CA Landscaping Rules: Grass Height Limits (2026)

San Mateo County does not impose a generic 'tall grass' nuisance height for an ordinary occupied residential lawn the way many cities do. Instead, grass control in the unincorporated County is driven by wildfire law. Under California Public Resources Code 4291, owners of buildings in the State Responsibility Area (SRA) and in designated High or Very High Fire Hazard Severity Zones must maintain defensible space, and Fire Safe San Mateo's defensible space guidance (reflecting the statewide standard) instructs owners to 'cut or mow annual grass down to a maximum height of 4 inches.' Defensible space is organized into Zone 1 (0-30 feet from buildings, structures and decks) and Zone 2 (the reduced-fuel zone extending out to at least 100 feet or the property line). Trees in these zones must be spaced and limbed-up, and dead vegetation removed. Enforcement is by CAL FIRE in the SRA and by the County Fire Marshal/local fire authority in Local Responsibility Areas. Outside fire hazard zones, overgrown vegetation that creates a fire hazard on vacant or open land is handled as hazardous-vegetation abatement (see Weed Ordinances), not as a lawn-height rule.