Gardening: Best way to improve soil is to add compost

I recently got a question from a reader about where to get good soil and compost. Part of her request was for “organic” soil and compost.

The Spokane region is home to a wide variety of soils depending on the underlying geology and your proximity to the Missoula flood channels. South of Spokane on the Palouse, we find the wind-blown Palouse loess, a fine-grained soil that supports the irrigation-free grain crops. Spokane’s South Hill has a lot of clay that has weathered out of the basalt. West of Spokane, soils are a mix of Palouse loam and the remnants of the glacial flood scouring and outwash. North of Spokane toward Deer Park, the soils are sandy remnants of the floor of glacial Lake Spokane that backed up behind ice dams to the west. In the Spokane Valley, glacial outwash gravels and, in some places, boulders fill the valley floor while the hillside are often a clayey sandy soil formed from the ancient, deformed granites.

Regardless of your soil type though, the best soil amendment to improve your soil is straight compost. It increases the water holding capacity of the soil, provides some nutrients, increases microbiological activity and slows erosion.

So, what is compost? By definition, it is decayed plant material made from garden trimmings, crop debris, tree trimmings, spoiled vegetables and sometimes manures piled together so that bacteria can begin to break down the debris into a crumbly dark material. In Spokane, most of our compost comes from the Barr-Tech Composting, west of Spokane. Barr-Tech collects the “clean green” garden waste we take to the transfer stations, grinds it into long piles and then blows air into the pile to enhance the biologic process that converts it into compost. The material is then sold to local soil material companies for sale back to us. It’s recycling at its best.

In an interesting twist, my reader was asking about organic compost. By this they meant compost that is officially certified organic by one of the many organic certification organizations. Unlike the National Organics Program-certified vegetables we buy at the store, compost can’t be “certified organic” like our food. Only food and fiber crops can be certified organic. Because compost comes from so many diverse sources and goes through the composting process, it can only be “certified for use on certified organic farms” and by extension our gardens. The Washington Department of Agriculture does this certification.

It is the same for garden soil blends sold by the soil material companies. They aren’t certified organic but certified as usable on organic farms. Again, their soil stocks come from such a wide variety of sources, it’s impossible to know the original source and how it was handled.

Sometimes, compost is mixed with other materials such as processed sewage sludge which technically is from a biologic source, human manure. However there is a lot of debate around this practice. If this is a concern, Barr-Tech does offer their Barr-Tech Green compost which is free of sewage sludge.