Silage tarps are made of 5 mil polyethylene plastic. Use silage tarps to create a stale seedbed through the process of occultation, which involves blocking light. Prepare your bed as you normally would, then cover with the silage tarp. The tarp will create a warm, moist environment, causing weed seeds in the soil to germinate. However, since the silage tarp blocks light from reaching the soil, the weeds will subsequently die. As the dead plant matter collects under the tarp, earthworms will rise to the surface to feed on the plant matter, enriching the soil. The end result is a fertile and weed-free environment for your crops. Hold silage tarps in place with sandbags.