A big part of gardening is finding solutions to plant-related challenges. I found myself in that position, faced with a hillside yard that was too steep to safely mow, and too large to easily dig up and replant. The solution to addressing this challenge was sheet mulching, a method that can be used on many types of areas that a gardener wants to prepare for new planting.
The gardening literature includes a wide range of instructions for implementing this process, which is also referred to as lasagna composting. This article will describe the major considerations and this gardener’s recent experience.
Sheet mulching achieves two major goals. First, it kills the grass and weeds that would prevent a new garden from flourishing, and second, it creates good soil for the new plantings. The main materials are sheets of cardboard or paper, at least one source of carbon (referred to as “browns” in composting terms), at least one source of nitrogen (referred to as “greens” in composting terms) and water.
The cardboard layer is placed directly on the target area, ideally after mowing as low as possible, then covered with the browns and greens. Make sure that the cardboard is devoid of any tape or staples, with as little ink as possible. Larger sheets make the process easier, especially if you are covering a large or sloped area. Secure the cardboard with stakes and bricks as needed until the biological processes are sufficiently underway to stop the material from slipping or blowing away. Once the cardboard is in place, begin regular watering.
Collecting and adding the browns and greens will be the most time-consuming work of the project. Since sheet mulching is a cold composting process, you want to avoid any materials that would introduce unwanted seeds or diseases, or that would take too long to decompose. For example, use cut grass instead of weeds from your garden or food scraps; shredded leaves or shredded newspaper is better than branches. Watering after each new batch of materials is applied will help keep the material in place and allow for the natural decay to occur faster. All of the cardboard layers should be fully covered with sufficient material to maintain several inches of coverage even after settling.
When is the right time of year to sheet mulch? There are sound arguments to be made for both spring and fall. I did a test area in the spring, and it was ready for planting by the fall. Since dry leaves were not available in the spring, I had to work harder to secure good “browns,” but found that shredded newspaper mixed well with grass clippings. This area was able to be pre-seeded with a light covering of straw in late fall and should be ready to produce in early spring.
In the fall, it is much easier to apply a mix of grass clippings and chopped-up fall leaves to the secured cardboard. Either spring or fall preparation will benefit from the addition of mushroom manure or clean soil, primarily to help secure the compost material in place – this layer is not necessary, but certainly helpful. The key outcome is to have an area where the mulching material has broken down, requiring only minimal preparation with a metal rake before planting.
A sheet mulching process is now underway in front of the Beaver County Courthouse where Master Gardeners are preparing to plant a demonstration garden in the spring. The approach to this garden involved laying out thick paper and covering it with a blend of soil and bark mulch.
There are lots of variations on the details of preparing a new area for planting with sheet mulching. But it is a long-standing solution to the challenge of preparing a new garden. If you have more questions about this process, please contact our Garden Hotline at [email protected]. Master Gardeners are on hand year-round to answer all your plant and pest questions.
Katie Klaber is a Master Gardener with Penn State Extension, Beaver County.