Sheet Mulching is a method of creating no-dig garden beds by layering compost materials to suppress weeds and grasses and improve the soil. It is especially useful when converting a relatively large grassy area, like we had, into cultivable land with little equipment or machinery.
Mulching is extremely important in permaculture. It insulates roots and the soil, retains moisture and nutrients, provides a habitat for life, and increases organic matter that improves soils structure and biology. Tilling and disturbing the soil does the complete opposite, leading to soil degradation and erosion over time if done too intensively. In this process we want to build the soil up instead of removing material.
Sheet Mulching is an example of the Permaculture Principle “Observe and Interact”. This is fundamental to permaculture: observing how ecosystems behave and replicating it in your own design. In this case, the layers of mulch are meant to mimic the natural litter on a forest floor. It begins with cut or flattened weeds and grasses, then a concentrated compost layer (see last week), followed by a weed barrier (the only layer not present in Nature), and finally alternating nitrogen and carbon-rich mulch layers that represent newly fallen forest litter and will decompose into compost over time. Ideally this should be done in the fall so that the layers can break down over the winter, producing a medium that is easier to plant in.
This week was focused on the weed barrier: designed to prevent the germination and re-emergence of the weeds and grasses below it. We went with the typical method of using cardboard: an easily sourced material that is thick enough to block the light to the plants below, and a favourite of earthworms that will break down and till the cardboard into the soil.
We had begun collecting about a month ago, sourcing cardboard from bicycle shops (bike boxes are a perfect size), grocery stores, and the recycling bins of Macdonald Campus (Thank you to all of the centrifuge tube/wine/office chair purchasers). Now that the compost layer was completed, we were finally able to start laying it down. With the help of wonderful volunteers Siri, Evan, and Olivia, we covered most of our planting area before exhausting our cardboard supplies. The rest will have to wait until next recycling day!
We also covered the cardboard with some heavy clay topsoil donated by the Mac Farm to prevent it from flying away.
Although the point of the weed barrier is to kill the plants beneath it, there were a few that we wanted to keep. The field was littered with milkweed, and important plant for monarch butterflies, that we came up with some creative ways to avoid crushing.
Elevitch, Craig and Kim Wilkinson. “Sheet Mulching”. Agroforestry. Agroforestry Net, Inc, 1998, http://www.agroforestry.org/free-publications/sheet-mulching. Accessed 9 Jun. 2017.
“No-Dig Garden Beds”. IFAS Extension. University of Florida, http://solutionsforyourlife.ufl.edu/hot_topics/sustainable_living/no_dig_garden.shtml. Accessed 9 Jun. 2017.
“Sheet Mulching-Lasagna Composting”. Extension Service Lane County. Oregon State University, Jan. 2013, http://extension.oregonstate.edu/lane/sites/default/files/documents/lc731sheetmulchmay2015_0.pdf. Accessed 9 Jun. 2017.