The Bay-Friendly Landscape Guidelines recommend incorporating quality compost into the soil at a rate sufficient to bring the soil organic matter content to 3.5% to 5% by dry weight.
California's Water Efficient Landscape Ordinance (WELO) now requires the use of compost on permitted landscapes. Find out more.
Compost is the product of controlled biological decomposition of organic materials, often including urban plant debris and food waste. It is an organic matter resource that has the unique ability to improve the chemical, physical, and biological characteristics of soils or growing media. It contains plant nutrients but is typically not characterized as a fertilizer. (Excerpted from U.S. Compost Council's Field Guide to Compost Use)
Compost Best Practices
- Have a professional soil laboratory analyze the soil and recommend the amount of quality compost needed to bring the soil organic matter content to 3.5–5%.
- Incorporate the compost into the planting area topsoil to a depth of 6 inches.
- Use compost that is OMRI-certified or that is part of the USCC Seal of Testing Assurance Program and meets their compost parameters.
- Integrate this practice into a soil management plan.
- When purchasing imported topsoil, specify that it be amended with compost.
- If your site’s plant palette primarily includes California native species that are adapted to soils with little or no organic matter, consider skipping the compost amendment.
Indicators of Quality Compost
Look for these characteristics to identify quality compost:
- Dark brown color
- Sweet, earthy smell
- Small, fairly uniform particle size
- No weed sprouts
- Feedstock is no longer recognizable
- The producer can tell you the peak temperatures (and how long the compost stayed at those temperatures)
- A nutrient analysis is available from the producer upon request
- Compost is certified by the US Composting Council’s Seal of Testing Assurance (STA) Program
- For information about composting for home gardeners, visit our Gardening section
- Bay-Friendly Landscape Guidelines: Sustainable Practices for the Landscape Professional
- Local sources for compost, mulch and cardboard
- Model Bay-Friendly planting specifications
- Caltrans compost calculator
- U.S. Composting Council, Seal of Testing Assurance (STA) program
- U.S. Composting Council, Field Guide to Compost Use
- Washington State's Building Soil: Guidelines and Resources for Implementing Soil Quality & Depth BMP T5.13
- Organic Materials Research Institute's directory of OMRI Listed products, including compost
- Institute for Local Self-Reliance's report, State of Composting in the U.S., and other reports on composting