A plastic tarp can act as an effective and inexpensive weed barrier in gardens. The tarp can be used as a permanent soil cover, much like landscaping fabric, or a temporary aid when fumigating soil for weed control. When using a tarp as a permanent barrier, use a black plastic tarp. Black plastic, according to Ohio State University, is effective as it blocks out the most sunlight, prohibiting weeds from germinating in the soil.
Lay the tarp down on top of the soil. Ensure it is laying flat and covering all the soil.
Place a 2- to 3-inch layer of mulch on top of the plastic tarp. Wood chips, sand or small-sized gravel works well.
Clear the mulch away from areas where you wish to plant. Cut a hole in the tarp with scissors 1 to 2 inches wider than the size of the plant's root ball.
Dig out the soil exposed through the holes in the tarp with a small garden shovel. Make the depth of the holes approximately 1/2 inch deeper than the height of the root ball.
Place the plants in the holes and fill around the root balls with the soil. Clear off any excess soil from the top of the tarp to inhibit weed growth on the surface.
Replace the mulch around the plants, leaving 1 to 2 inches of space from the plant stem to allow water to properly penetrate into the exposed soil below. Water will penetrate the soil, but the space between the plants is protected from weed growth by the plastic tarp.
Apply a soil fumigant, such as dazomet, to the soil, following the product's directions. Use a rototiller to a depth of 2 to 3 inches to mix the fumigant with the soil.
Water all the soil thoroughly.
Cover the moist soil with the tarp, weighing down the edges with rocks or wood. This will keep the tarp from blowing away and help seal in the soil's moisture.
Remove the tarp one week later. Use a rototiller on the soil to a depth of 2 inches. Do not till any deeper, as this may bring dormant weed seeds to the surface and promote new weed growth.
Wait 14 to 20 days before planting in the soil to ensure new plants are not killed by fumigant residue.