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gardening with Groco

Compost made with biosolids is an effective soil amendment for lawns, gardens, and landscaping. Loaded with nutrients and organic matter, biosolids compost builds healthy soil, retains moisture, and produces lush plants with beautiful blooms.

King County contracts with Sawdust Supply , a local company, to produce GroCo compost. Available since 1976, GroCo has a loyal following among landscapers and gardeners, who know it is clean and weed-free.

GroCo compost made with Loop is made with local materials - three parts sawdust are mixed with one part Loop biosolids and composted for a year. The finished product is a stable, fine-textured, “exceptional quality” biosolids product.

GroCo has many benefits for plants and soil, including:

  • Enriches soil with a full suite of plant nutrients, including nitrogen, phosphorus, potassium, iron, calcium, magnesium, and zinc
  • It's rich in organic matter, which releases nutrients slowly for use by soil microbes and plants.
  • It improves soil structure and aeration, increasing water infiltration and making compacted soils more porous and helps reduce soil erosion
  • It acts like a sponge to help soil absorb and hold moisture, reducing the need for summer watering

GroCo Safety & Quality

Each batch of GroCo is laboratory tested to ensure it meets Exceptional Quality standards for biosolids products and that it meets Washington State standards for composts. GroCo is also tested for disease-causing micro-organisms such as bacteria, viruses and parasites. Biosolids treatment kills more than 95% of such organisms and the composting process destroys any that may remain. Laboratory results confirm that pathogenic organisms are not present in GroCo.

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How do I use GroCo compost?

As a soil conditioner:
  • Loosen existing soil; spread compost 1 to 3 inches deep on the area you will be planting, then till or spade into the soil
  • For individual planting of your shrubs and trees, mix GroCo half-and-half with existing soil

As a lawn conditioner:

  • Spread up to 1 inch of GroCo over your lawn in early spring or fall. 

In container gardens, window boxes and potted plants:

  • Combine equal parts GroCo and sandy loam soil, mix thoroughly, and place in container.

Where can I get GroCo?

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GroCo made with Loop is available at Sawdust Supply Inc and other materials yards throughout the greater Seattle area.

Visit Sawdust Supply at 6314 7th Ave S, Seattle 98108 or call 206-622-5141.