Mendocino County, CA Landscaping Rules: Composting (2026)

7) into county law for anyone who needs a building, planning, or landscape design permit for a new single-family, multi-family, public, institutional, or commercial project with more than 500 square feet of landscape, or a rehabilitation of an existing landscape larger than 2,500 square feet. 6(a)(3)(B), (C), (D), and (G) and submit a landscape design plan with a soil preparation, mulch, and amendments section. The compost rate is a minimum of four cubic yards per 1,000 square feet of permeable area, incorporated to a six-inch soil depth, though soil that already tests above 6% organic matter in the top six inches is exempt from adding compost and tilling.

Mulch must be applied at least three inches deep across exposed soil and planting areas, with exceptions for turf, groundcovers, and direct-seeding areas where mulch would interfere, and up to 5% of the landscape may be left unmulched as designated insect habitat if the plan calls it out. Recycled or post-consumer organic mulch takes priority over inorganic or virgin-forest material unless it isn't locally available, and mulch is not required where a local fuel modification plan or other ordinance prohibits it, a carve-out relevant in the county's wildland-urban interface fire areas. If the California Department of Water Resources later tightens the referenced MWELO sections, the stricter state standard automatically governs under subsection (D).