This article was excerpted from Growing an Edible Garden by Gary Pilarchik, Chiara D’Amore, PhD, published by Cool Springs Press.
Sheet mulching is an inexpensive, natural way to prepare areas to become gardens. The basic idea is to use thick layers of natural materials (paper, cardboard, compost, etc.) to block sunlight from whatever plants you want to replace (grass, “weeds,” etc.). These will die off in a way that nourishes the health of your soil and creates the foundation for the plants you want to grow. In warmer areas, the best time of year to sheet mulch is the fall, so everything can decompose over the winter, or the spring right before things start to green up. It takes about six months for areas you have sheet mulched to be optimal for new planting if you need to dig into the ground.
Once you have identified the area you want to sheet mulch (along a foundation or fence, at the base of raised beds, etc.), the items you will need for the project include:
- Lawn mower or weed wacker—to get plants down to a low level
- Tools—wheelbarrow, shovel, rake, spading fork or garden knife, etc.
- Biodegradable weed barrier—newspaper or cardboard
- Brown mulch—leaves, straw, wood chips
You can likely obtain both the weed barrier and the brown mulch at your local recycling center or by asking community members to share their landfill-bound resources with you. You might even be able to borrow the tools. Once you have all of your supplies handy, including a source of water, the following are the steps for sheet mulching:
- Get low: Using your lawn mower or weed wacker (depending on what you are trying to get rid of), cut the existing plants down to the lowest level. You don’t want them to grow back, so cutting them all the way down is helpful to your process. Leave any grass clippings as part of the natural mulch, but if you have plants like thistle that you want to get rid of, be careful to remove seed heads so they don’t sprout right back. If you have woody plants that need to be removed from the area you are sheet mulching, pull them out by hand or dig them out with a shovel, trying to remove as much of the root base as possible. This is the time to get rocks or branches out of the area too so you have a smooth surface for the next step.
- Support the soil: If the area you are working in has compacted soil, you can use a spading fork to gently loosen the soil and make holes for nutrients to enter. You shouldn’t till or turn over your soil because it disrupts the soil ecosystem, which you are working to enhance with sheet mulching. If you are planning to put bigger plants into your new garden area (fruiting shrubs or trees), you can put them in at this time and then mulch around them so you aren’t digging through all the layers of the sheet mulch later.
- Layer away: The biggest part of the project is to create the layers of organic matter—the sheets, or the lasagna layers if it helps to think about it that way:
- Evenly spread about 1 inch (2.5 cm) of compost, leaves or straw on the ground. This will attract worms and beneficial insects to help loosen up the soil. Spray the whole area with water to help kickstart the process of decomposition and help the next layer stick.
- Lay out thick layers of newspaper or cardboard (at least 3/4 inch [2 cm] thick) over the entire area to create a weed barrier. It is really important to substantially overlap the edges of your paper product so there are no gaps that allow sunlight to get through and encourage your old ground cover to grow back. Also make sure that you have removed glossy pages from the newspaper and tape from cardboard (don’t use glossy or wax-covered cardboard at all), since these elements don’t decompose well. Spray the whole area with water again.
- Evenly cover the weed barrier layer with 2 to 3 inches (5 to 7.5 cm) of compost, which will help the decomposition process and support soil health.
- Add an even layer of 3 to 4 inches (7.5 to 10 cm) of organic material such as leaves or wood chips. This layer helps ensure that light doesn’t penetrate to the ground, and it supports beneficial microorganisms. At this point your mulch layer should be about 8 inches (20 cm) tall. Water it one more time and wait!
If it is important to add some visual appeal to the area while the sheet mulching is doing its work, you can add a couple of inches of compost to the top and add small plants into the space, using a gardening knife to cut small holes in the paper layer so the roots have a way to access the soil.