San Mateo County, CA Property Maintenance: Weeds & Overgrown Grass (2026)

Two distinct frameworks govern vegetation in unincorporated San Mateo County. First, as a property-maintenance matter, the Planning and Building Department's Code Compliance Section applies standards on its Notice of Violation forms that are drawn from the International Property Maintenance Code: all overgrown and dead weeds and vegetation must be removed from the exterior of the property, with growth maintained at a maximum height of 18 inches or less. Overgrown vegetation, like accumulated refuse, can be treated as a public nuisance and abated through the County's standard process — a Notice and Order to Abate, a 10-day period to correct, and County abatement billed at actual costs plus a 15% administrative fee if the owner does not comply. Second, for wildfire risk, hazardous weeds, brush, and combustible vegetation are abated under California Health and Safety Code Section 14875 et seq. and the County's fire-prevention authority, which the County and CAL FIRE apply through seasonal weed-abatement programs; defensible-space clearance distances (such as 100 feet around structures under Public Resources Code Section 4291) are governed by state law, not a unique County grass-height number. Residents should treat the 18-inch figure as the County's general property-maintenance threshold and follow defensible-space guidance for fire-hazard severity zones, which can be more demanding.