Sheet Compost this Fall for Healthy Soil in Spring

A mulched rhododendron.

Improve the soil during the winter without digging by using sheet composting. Sheet composting refers to the use of thin layers of compostable material laid out over the soil like a thick mulch. As it biodegrades, the soil’s structure and fertility is improved from the top down. By layering high-carbon wastes with nitrogenous plant refuse, you essentially construct a thin, wide “two-dimensional” compost pile.

Use a blend of dry brown leaves or woody stems (chipped, chopped, or not); fresh manure, fresh grass clippings; green-manure foliage (in the summer) such as buckwheat, vetch, bell beans and clover; wet kitchen garbage or scraps (no meat scraps, as they’ll tend to attract hungry animals and/or smell bad); and green weeds from the garden before their seeds ripen.

Experiment with a ratio of one part green matter (including manure) to three or four parts dry, dead brown matter. Water the dry materials as you’re layering. NOTE: sheet composting doesn't generate enough heat to kill weed seeds, diseases or pathogens. Cover the area with five to ten sheets of newspaper and cover the newspaper with a weed-free mulch; this should take care of the nasties. The sheet composting slowly helps improve soil all winter while allowing the gardener to quickly dispose of large quantities of compostable materials and avoid unnatural tillage. The sheet-composted area will require more irrigation the first year or two as the roots grow into the soil below the sheet compost.

More-and-more gardeners are using newspaper (the non-slick pages) and cardboard (with the packing tape removed) to suppress and kill lawns, weeds and unwanted vegetable sprouts. (Also see our blog on growing garlic). The temporary layers are used as a “natural herbicide” under a layer of attractive, weed-free mulch.

Three trees mulched out to their driplines.

However, according to Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor, Puyallup Research and Extension Center, Washington State University, in her blog “The Myth of Paper-Based Sheet Mulch”:

• When wet, the layers of paper can create an impermeable barrier to water and air exchange.

• Garden pests, moles and gophers can hide under the newspapers and cardboard sheet mulches. In her experience, termites preferred cardboard over wood chips.

• If allowed to dry out, irrigation water may sheet away rather than seep through the layers, especially in arid climates or well-drained soils.

Organic mulches work better than cardboard and newspaper to prevent weed growth. She says to use six to eight inches of a “weed-free” compost or mulch such as rice hulls, straw or leaf mold.

“Arbor Mulch”—wood chips composted with green waste at what used to be called the dump.

More encouraging is her feeling that newspaper and cardboard sheet mulches have been effectively used in home gardens where soil is continuously worked and irrigation, in the arid west, is used. She does suggest newspaper and cardboard sheet mulches can be effective for annual beds.

Sheet compost before the snow falls then sit back and let nature improve your soil.

BIO: Robert Kourik's books, blogs, and articles bring science to gardening. He has designed gardens for three decades and is a pioneer of edible landscaping, the art of growing food plants among ornamental plants.  He works throughout California and the country. Visit Robert's blog Garden Roots or go here to buy his books.