Sheet-mulching is a quick way to convert your lawn to usable garden space. Fall is also the best time to sheet-mulch your garden. Depending on the area being covered, this might only take 30 minutes to an hour, and you can plant directly through the cardboard and into the grass.
Sheet-mulching, as opposed to the more traditional organic gardening techniques of ‘flipping over the soil’ or ‘double-digging’, protects the soil organisms from damage. These organisms (bacteria and funghi) are integral to the process of transferring soil nutrients (vitamins and minerals) to the plant in a form that the plant can use, and will affect the nutrient content in the food that you grow.
This is how it works:
Cardboard is placed directly over the ground and, within a week, the grass under the cardboard begins to rot. Worms come up from the soil to eat the decomposing grass and turn it into worm castings (compost), which makes a great free fertilizer (5% Nitrogen) for the soon-to-be-planted plants.
- Find some plain cardboard with only black ink (colour ink on cardboard is toxic) – moving boxes or large sheets that cover palettes are best. You’ll want enough to do 2 layers of cardboard. When calculating how much you need, reduce the size of the cardboard by at least 1 foot to account for 6 inches of overlap on the sides.
{There is a bit of an art to sourcing and laying cardboard for sheet-mulching, but basically you want to find large pieces that are easy to overlap. Small folded boxes, with gaps between the tabs when flattened, are not worth the trouble if you’re covering a large area, as grass can easily grow through the cracks if they’re not meticulously covered. Save yourself some work and cover more ground by looking for larger sheets or boxes.}
- Get some compost to cover the cardboard (the compost helps to break down the cardboard even faster)
- Make or find a good source of compost- one that has been turned/aerated and heated to the mandatory 160°F to kill pathogens and weed seeds.
- Remove tape and sticky labels, and lay the cardboard so that all of the sides overlap by 4-6 inches. Do 2-3 layers.
- Wet the cardboard using a garden hose before adding the compost to the top.
- Top with at least 2 inches of compost. To plant immediately, use a Stanley/exacto knife and
cut an X in the cardboard to the size of the root ball to be planted.
- Dig the hole and add a handful of compost or worm castings to the base of the hole and plant your plant. Top with a bit more compost (remember, nutrients always flow downwards), and water in the plant well.
Top with a few inches of mulch. This could be shredded leaves, wood chips, organic straw (hard to find but worth it!), or any organic matter that you have on site. In a forest, ‘mulch’ is what you find on the forest floor, so have a go at mimicking this system in your garden; your soil will thank you.
