King County, WA Landscaping Rules: Composting (2026)

Chapter 10.04 of the King County Code makes it unlawful for a property owner to deposit or let solid waste accumulate on private land, but K.C.C. 10.04.080(B) builds two carve-outs into that same subsection: composting and permitted recycling. Under 10.04.080(B)(1), the use of a compost pile or bin shall not be prohibited if the use and maintenance thereof is in such a manner as to prevent the attraction, breeding, harboring, or any combination thereof, of insects and rodents. The code sets no maximum pile size, no property-line setback and no permit requirement for residential composting; the only condition is pest management.

That tracks the county's own definitions in K.C.C. 10.04.020: composting means the biological degradation and transformation of organic solid waste under controlled conditions designed to promote aerobic decomposition, and material only counts as composted material once it has gone through that controlled process; natural decay left uncontrolled does not qualify. If a compost pile or bin turns into a rodent or insect harborage, the exception in 10.04.080(B)(1) stops applying and the pile falls back under the general littering and unlawful-dumping prohibition in 10.04.080(A), which the health officer can enforce through the prosecutor's office and King County Code Title 23's civil-penalty and citation process under K.C.C.

10.08.100. This rule sits inside the unincorporated-area solid waste code; Seattle, Bellevue and King County's other cities run separate codes and are not covered by it.