When most people think of the ideal lawn, they think of well-maintained, bright green turf grass. We perceive well-maintained yards as aesthetically pleasing to the human eye, but they’re not pleasing toward the environment. Turf grass is largely a barren landscape for wildlife and contributes to a loss of urban biodiversityBiodiversity The variety of species present.. Most lawns tend to consist of only one or two species of grass, which dramatically limits the number of wildlife they can support. Likewise, maintaining a green lawn requires a lot of time, upkeep and water – which can get expensive. More and more people are looking to reduce or remove their lawns to create healthy, thriving landscapes.
Sheet mulching, also called sheet composting or lasagna mulching, has become a popular gardening technique to help people convert their lawns to beautiful gardens while at the same time improving soil health and soil structure and suppressing weeds.
The beauty of this technique is that many of the ingredients – cardboard, leaves, lawn clippings, straw bedding, compost, and wood chips – are items you can collect for free or relatively cheap from around your own home, your neighbor’s yard, or your friendly neighborhood arborist.
In its simplest form, sheet mulching is a process where compostable material, such as cardboard or newspaper, is covered with organic material, such as manure, straw, or wood chips. Think of it as a gigantic compost pile that spans your entire lawn. As with any compost pile, sheet mulching needs the proper proportions of carbon, nitrogen, oxygen, and water to break down organic material into a good growing medium. These materials are then layered on top of one another – hence the name lasagna mulching – to create nutrient-rich soil that is perfect for starting a new garden.
Here’s the recipe:
Step 1: Preparing Your Site
Begin by mowing your lawn to the lowest possible level. Save any lawn clippings from this step to use later in the process.
If your lawn is bordered by a concrete walkway or driveway, make sure to dig out the edges. This will help remove any remaining grass. Likewise, if there are any plants that you’d like to keep, dig a small trench around the base of each one to remove any grass.
Step 2: Lawn Suppression
This is the most important step in the process!
The key to creating beautiful soil is to attract beneficial microbes, such as mycorrhizal fungi that attach to plants’ roots and help them absorb water and nutrients. Luckily, mycorrhizal fungi love the cellulose and glue that is found in cardboard or newspaper.
Start by collecting and breaking down cardboard boxes from friends and family, neighbors, dumpsters, or grocery stores. Just don’t use any cardboard with a shiny finish – these generally don’t decompose. Greasy pizza boxes work great for sheet mulching projects as they usually can’t be recycled but can easily break down.
Once you’ve collected your cardboard, remove any tape or staples, and lay it flat over the area you would like to convert. This first layer smothers any existing grass or weeds by preventing light from reaching the plants. If you are using newspaper, you’ll want to layer at least 10-15 sheets to create a strong suppression barrier. Be sure to overlap your cardboard by at least 6 inches to prevent tenacious weeds from weaseling through the gaps.
With the cardboard in place, wet it down thoroughly until it becomes heavy and starts sticking to the ground. This will start the decompositionDecomposition The process of organic matter breaking down into smaller parts. process and will help keep the cardboard in place as you add your additional layers.
Step 3: Start Layering
Here is where your other materials come in. Your goal is to have approximately 8 inches of green waste and compost covering that cardboard. Remember you’re basically creating a large compost pile, so you want to alternate layers of carbon (such as dry leaves, shredded newspaper, or straw bedding) and nitrogen (such as grass clippings, kitchen scraps, manure, or compost).
Start by adding a 1-inch layer of nitrogen-rich material, like manure or the lawn clippings, directly on top of your cardboard. If you use lawn clippings, apply them lightly and mix them with other materials. This will stop them from getting matted and forming a barrier that repels water.
Top this nitrogen layer with a layer of carbon-rich material such as straw bedding or leaves. Follow the carbon layer with another layer of nitrogen. Finally, add a 4-8-inch layer of bulk carbon-rich material such as wood chips.
Next, comes the hardest step in the process … waiting.
Sheet mulching is a slow process. You’ll need to allow three to four months for all of your materials to sufficiently decompose and allow for planting. It is possible to shorten this wait time by fully removing your lawn when preparing your site. If employing this method you risk having grass or unwanted weeds sprout before your new soil is ready. Sheet mulching projects are best to start in the fall. By having your layers in place before the rainy season, Oregon’s wet winters can supply the needed moisture.
Step 4: Planting
Once your materials have broken down, it’s time to start planting!
You can add another layer of compost on top of your newly formed garden to provide additional nutrients. We recommend planting native plants to provide shelter and food for local wildlife and support pollinators. East Multnomah Soil & Water Conservation District hosts an in-depth list of native plants to our region.
To see this process in action, watch our How to Remove Lawn by Sheet Mulching video.