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King County Washington home

Compost

Compost improves soil by making it richer and better at holding air and water. It also helps control weeds, prevents erosion, and reduces the need for extra water, fertilizers, and pesticides. Compost is useful for farming, erosion control, stormwater management, and land restoration.

In King County, compost is made from food and yard waste, manure, and biosolids. One product, Loop® compost, is created by combining woody materials with Loop® biosolids—a nutrient-rich material made by recycling human waste and food at wastewater treatment plants.

Best Practices

  • Use compost to improve soil health and reduce the need for chemicals.
  • Choose locally made compost to support recycling and cut transportation impacts.
  • Apply compost for farming, landscaping, erosion control, or stormwater management.

Policy and Goals:

The use of compost is required by King County KCC Title 18.30 – Compost Procurement and Use and in accordance with Washington State RCW 42.19A. 150. Departments must plan for compost use in:

  • Landscaping projects
  • Construction and post-construction soil amendments
  • Projects to prevent erosion, filter stormwater, support vegetation growth, or improve road stability (per KCC Title 9)
  • Low-impact development and green infrastructure to filter pollutants and manage water on-site (per KCC Title 9)

Supporting Policies:

From Washington State RCW 43.19A.120 – Use of compost products in projects:

  • If compost can be used in a project, the state agency or local government must use compost products.

From King County's 2025 Strategic Climate Action Plan (SCAP),

  • GHG 56. Improve quality and increase reuse of commercially produced compost

From King County Code (KCC 28.86.090):

  • Use biosolids-derived products as soil amendments in landscaping projects funded by King County.

From the King County Comprehensive Plan,

  • Agencies must use recycled organic products, such as compost, whenever possible.
  • Promote compost use to restore organic content in soil lost through development, agriculture, and resource extraction.

Quick Tips

Choose

  • Compost-amended topsoil for landscaping, garden beds, and planter boxes
  • Biosolids-derived soil products
  • Locally sourced or certified organic compost
  • Compost socks made from recycled or biodegradable materials for erosion control, sediment filtration, and stormwater management
  • Mulch made from composted yard waste to reduce water use and suppress weeds
  • Compost teas or extracts as natural fertilizers for plants

Avoid

  • Conventional soil with no compost additive
  • Soil or amendments with synthetic fertilizers only

End of Life

  • Compost yard waste, clean wood, mixed loads, and non-organic material through a certified composting vendor
  • Compost food scraps, coffee grounds, and other accepted organic materials
  • Separate compostable packaging (PLA cups, plates, napkins) from landfill trash streams

An EPA checkmark indicates a certification or standard is recommended by the U.S. Environmental Protection Agency (EPA).

 

Recommended Material

A product of King Country, Loop biosolids is made from cleaning and recycling all the water that comes from homes and businesses, producing a nutrient-rich soil builder.

Best Practices

  • Use Loop® to enrich soil and support plant growth.
  • Apply it in landscaping, farming, or land restoration projects.
  • Choose Loop® as a local, sustainable alternative to chemical fertilizers.



Technical Specification Language

King County's CompostWise Program

Washington Organic Recycling Council

U.S. Composting Council

Washington State Department of Ecology: Composting Guide

EPA: Reducing the Impact of Wasted Food by Feeding the Soil and Composting