Sheet Mulching

By Charlotte Torgovitsky

Sheet mulching is an excellent way to get rid of your lawn. Find out how in this step-by-step guide! The results take time, but as in nature, compost happens—and you will be rewarded with beautiful soil ready for planting!

Soil test

Before beginning, CNPS strongly urges you to test your soil for composition, minerals, and legacy issues (past owners’ soil treatments). Soil tests should assist you in making informed decisions about soil amendments.

When to start

Decomposition takes several months, so it’s best to sheet mulch an area months in advance of fall planting season.  Given time and summer heat, the layers of paper and organic materials will smother the grass and all of it will decompose into wonderfully rich and fertile soil.

Start small

Quantities listed here will conver an area of fifty square feet. To create fertile soils for California native plants, you will need:

• a 2 to 3 foot stack of newspapers,
• about 300 sq. ft of corrugated cardboard boxes,
• about 1/4 to 1/2 cubic yard of finished all-green compost (compost without animal manures),
• and approximately 5 to 7 cubic yards of bulk organic matter.

This list is meant only to serve as an example; if possible recycle what you have on hand, or use free materials that can be had for the asking. Neighbors will often save newspapers if you ask for them; appliance stores are a good source of cardboard. Cotton fabrics can take the place of some of the paper; coffee companies will sometimes give away burlap sacks, and you can also recycle old cotton sheets, towels, or clothing.

You can save lawn clippings, leaves, and shredded plant trimmings; straw bales are available cheaply if they become wet; and chipper bark is often dumped free of charge by tree companies. Be sure to ask the tree company what kind of trees make up the chipper bark; avoid Eucalyptus, California Bay, and Walnut. These trees contain chemical compounds that inhibit plant growth and their chipped bark is fine for use on pathways, but not in planting areas. You can also purchase materials.

Step 1

Water the area well before you plan to start the process. You will need to cut plants growing on the site to the ground. Don’t remove the cut vegetation because it will supply food for the decomposers. Roots of most weedy plants can be left in the ground, but woody stumps or pieces should be removed. A dried-out lawn can be left in place—sheet mulch right over it.

Step 2

This is a great opportunity to amend your soil and increase its fertility with an array of micronutrients. You can sprinkle acid soils with lime, and improve alkaline soils with a little gypsum or sulfur. Bonemeal and rock phosphate supply phosphorus, which is essential for root formation, early growth, and good seed formation. Kelp meal, greensand, or rock dust all add trace minerals.

Step 3

If the area is compacted, or you are dealing with clay, take the time to open it up just a bit before you start to mulch. Simply push a fork or spade into the ground and rock it back and forth to open up holes in the ground. Turning disrupts the soil ecology; so that hard work is best avoided! One of the very best amendments to apply is rock dust—simply sprinkle it liberally over the area.

Step 4

Apply a thin layer of nitrogen-rich materials. These can be fresh grass clippings, finished compost, blood or cottonseed meal. This layer will attract the earthworms, burrowing beetles, and other invertebrates that will help loosen the soil.

Step 5

Cover the area with about one-quarter inch thick layers of newspaper. Avoid using the glossy pages from the paper, and remove the staples and tape from the cardboard. Overlap the edges by three to four inches, and wet everything down as you work. The purpose of the paper is to create a light-blocking layer that will smother the weeds. An added benefit is that the worms also love the darkness and moisture the paper creates.

Step 6

Add another layer of finished compost or green materials on top of the newspaper, always wetting materials as you build the sheet mulch. All-green compost can be applied in layers up to several inches thick. If you’re recycling grass clippings, be sure to spread them out thinly.

Step 7

Add a layer of cardboard on top of the compost or any other green material. Be sure to remove all the tape, metal staples, or plastic if you are working with recycled cardboard pieces. Also be sure to overlap the edges liberally, and wet everything down as you work.

Step 8

Now you are ready to add the carbon-rich mulching materials in a layer up to six inches deep. This can be fresh or spoiled straw (avoid hay, which often contains seeds); stable sweepings (as long as there’s not a lot of manure included); chipped yard waste; deciduous leaves (not live oak leaves) or pine needles; or the chipped bark and leaves available from many tree trimmers.

Tip:  Sheet mulching can be built up to a depth of a foot or more. The top layer should be all one type of material (either straw or chipper mulch) for a tidy and uniform look that you can live with for several months.

Step 9

Water the sheet mulched area about once a week if the rainy season does not materialize, or if you are not sheet mulching during the rainy season.

When we replace lawns with native plants, our biodiversity benefits. Organic materials return to the earth, building rich and fertile topsoil that retains moisture, warmth, and oxygen. Such healthy soil is the underlying support of the entire web of life, and a resource center for healthy plants.

 

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Charlotte Torgovitsky is a member CNPS Marin County Chapter & founder of Home Ground Habitat Nursery.  Learn more about Charlotte’s garden on her CNPS Garden Ambassador profile.