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Compost, Mulch and Soil

WELO Requirements for Compost & Mulch

California's Water Efficient Landscape Ordinance (WELO) requires the use of compost and mulch in permitted landscapes. Learn more.

Incorporating compost in the soil and covering soil with mulch are two of the simplest and most beneficial practices for improving—and drought-proofing—virtually any landscape. 

Why use compost?

Quality compost teems with microorganisms—one teaspoon can have more than one billion beneficial microbes. Adding good quality compost before planting turf, annuals, perennials, trees and shrubs brings life to the soil and helps plants thrive. Organic matter in compost acts like a sponge, helping to retain more soil moisture. Compost helps improve problem soils—in particular those that are compacted, heavy clay or sandy, poor in nutrients, or contaminated with lead. Incorporating compost is one of the most important practices for a healthy landscape.

Why use mulch?

In nature, leaves and needles fall to the ground, creating an organic layer that protects and builds the soil. Recycled mulch produced from local plant debris can offer the same advantage in the landscapes you design and maintain, helping to control weeds, reduce evaporation of water from the soil, and reduce labor costs. Grass clippings, leaves and tree prunings that are chipped or shredded are types of recycled mulch—they're valuable and readily available resources, not waste products.

Find out more

Landscape professionals: Browse this Compost and Mulch section for detailed information about using compost and mulch.

Home gardeners: Visit our Gardening section for tips on using compost and mulch in your home garden, building a backyard compost bin, and removing your lawn with sheet mulch.

Compost-Climate Change Connection

Applying a layer of compost
StopWaste and Partners Fight Climate Change with Compost

Livermore, CA – A thin layer of compost applied to grasslands could help fight climate change by capturing carbon from the atmosphere and storing it in the soil, recent research shows.