Solarization to Kill Pests & Weeds
A useful technique to kell weeds and pests in large areas
Solarization is a way to control weeds and pests in the soil without using chemicals. Instead, you are using the power of the sun and clear plastic to do the work in about 6 weeks, depending on your climate. Unfortunately it does take some time, so planning ahead is important. But it is a very effective way to clear a large area of multiple problems at one time using no chemicals.
Solarization is best performed when you can remove much of the vegetation first before laying down your plastic. Mark off an area that is slightly smaller than the amount of plastic sheeting that you are using. Cut the weeds down as close to the soil as possible, either with a lawn mower or weed whacker.
Till the area to break up the sod. You can rent a roto tiller from a home improvement center or rental company or borrow one from a friendly neighbor if you don't own one. You can lay the plastic right over the grass and weeds, but it won't be as effective as when you till up the soil first. Tilling the soil brings weed seeds up to the surface where they can be killed off by extreme heat.
Once the soil is tilled, rake the area and remove any plants and roots that have been brought up by the tiller. If the area was heavily covered by weeds, you may want to till the soil one more time and rake any additional plant material that is brought back up to the surface. Tilling the soil once should be sufficient for most homeowners however. Once you have removed the majority of the plant material, level the area as much as possible and water the area well.
Choose a clear plastic that is at least 4ml or 6ml thick. This thickness is readily available at most hardware stores and home improvement centers and is thick enough to not disintegrate quickly in the sun. Trench the area around the soil you are solarizing. Starting at one end, lay the plastic on top of the soil, overlapping the plastic on top of the trench. Fill the trench with soil so that it holds the plastic in place. Pack the soil in the trench with your foot or the back of a shovel.
Extend the plastic tightly over the soil until you reach the other end and repeat the process of securing the plastic with soil inside the trench. Once these two sides are complete, secure the plastic on the remaining two sides making sure the plastic is pulled tight and touching the soil as much as possible. Make sure you pack the soil in the trench to secure the plastic, watering the trench lightly if necessary.
Depending on your climate, this process may take as little as 4 weeks or as much as 8 weeks. If you are having consistent temperatures above 75 degrees Fahrenheit with lots of sun and little rain, it won't take as long as a place that is having a lot of cloudy, rainy conditions with cooler temperatures. This is why summer is an ideal time for this method. What is happening is that the sun is heating up the soil's surface and the plastic is helping to amplify the heat and keep the heat in the soil. Ideally the heat will penetrate the soil's surface a good 4"-6", killing weed seeds and harmful pests. Studies have shown that beneficial insects and nematodes return quickly to the treated soil, especially after an application of compost has been applied to the soil's surface.
Once you remove the plastic, the soil can be planted or mulched immediately. It's best not to disturb the soil too much after you have solarized it as this could bring new weed seeds to the surface, but you should be ok if you need to dig down 4" or less.