Using black plastic to kill grass and weeds is an easy, inexpensive and environmentally friendly option for gardeners. De-sodding requires equipment rental and the purchase of fill, since the top 8 cm (few inches) of fertile soil will be removed along with the grass. Using a chemical weed or grass killer is not ideal in many situations, as the chemicals can inhibit the growth of future generations of plants. Chemicals can also have an adverse effect on the environment. Solarisation is a process that involves placing a black sheet of plastic over grass and/or soil (clear sheets are often used for soil solarisation). The plastic prevents sunlight from reaching grass and weeds, thereby killing the unwanted vegetation. The black colour of the plastic attracts sunlight; the sun heats the soil, killing fungi, bacteria and nematodes while promoting soil health since the heat triggers the release of nutrients from organic elements in the soil. Once the process is complete, the old grass can be removed with a pitchfork or you can use a rototiller to turn the soil; the dead grass will release nutrients as it degrades.
Wait until the late spring or early summer before performing the solarisation process. This process cannot be performed when the grass is in a dormant phase and lots of warmth and sunshine will be required.
Delineate the area of grass that will be killed. This can be done using spray paint; special spray paints are created specifically for marking grass and athletic fields; this paint will gradually rinse away. Paint the line border about 5 cm (2 inches) outside of the area that will be covered with plastic.
Unroll the black plastic sheeting and cut it at a length that's about 8 cm (a few inches) longer than the delineated area of grass. For large areas of grass, the sheeting will be put down in strips beginning in the centre of the area and moving out toward the edges.
Lay the plastic over the grass that will be killed and insert anchors through the plastic and sink them into the ground. The anchors are U-shaped pieces of wire; they should be placed around the perimeter of the plastic, every 15 to 30 cm (6 to 12 inches).
Repeat steps 2 and 3 if working on a larger area of grass that requires multiple sheets. Overlap the sheets by approximately 10 cm (4 inches) to ensure good coverage.
Fold the edges of the plastic (over or under, it won't affect the end result) to make the plastic fit within the delineated area. Fold before inserting the anchors through the plastic and into the ground. It's better to avoid cutting a large piece of plastic because the sheet may shift during the cutting process; resulting in a sheet that's the wrong shape or size.
Leave the plastic in place for two to four weeks. If you're performing this process during the summer, a couple of weeks of hot, sunny weather will be sufficient. If you're performing this process during the spring or autumn, with cooler temperatures and/or lots of cloudy days, leave the plastic in place for approximately one month.
- Donald Paige; Master Gardener; Punta Gorda, Florida
- Weekend Gardener: Soil solarisation
- When marking the grass to delineate the area that will be covered with plastic, stand back and look at the area from different angles once it's marked. Shapes can appear distorted close up; it's best to assess the area from a distance or from a different angle.
- When overlapping sheets, you can use one row of anchors (instead of one row of anchors per plastic sheet). They must be placed at the point where the two sheets overlap.
- To kill very small areas of grass, you can use black contractor bin bags in place of rolled plastic. These bags are made of a very thick plastic that will prevent light from penetrating; they are also durable so they will stand up to the elements.
- The anchors are sold in DIY centres and hardware shops that sell gardening supplies like weed tarpaulin or weed block fabric. The anchors are more commonly used for weed block fabric and weed tarpaulins.
- Opt for a spray paint that's designed specifically for marking grass. These spray paint cans have a nozzle that's designed for use while the can is upside down.
- Do not perform this process in the winter, late autumn or early spring. The grass goes into a dormant phase during the winter months; this even occurs in subtropical regions like southern Florida. This dormant phase makes the grass very tolerant and it's difficult to kill. In addition, cold temperatures will inhibit the solarisation process.