What is Solarization?

Now is a good time to cover your vegetable garden beds with plastic. Why? Well, this is a technique know as soil solarization. Solarization is a simple non-chemical technique that captures radiant heat energy from the sun. This energy causes physical, chemical, and biological changes in the soil (bad things are cooked out). These changes lead to control or suppression of soil born plant pathogens such as fungi, bacteria, nematodes, and pests along with weed seeds and seedlings. 

Solarization works in the same way as a greenhouse where a transparent covering, in this case plastic sheeting, traps the sun's heat. After several days of sunshine, soil temperatures rise to as high as 140 degrees at the surface and over 100 degrees as far down as 18 inches -- hot enough and far enough down into the soil to sterilize it. It takes four to six weeks of sunny weather to pasteurize the soil at these temperatures.

Why Solarize?

Soil that has been solarized allows plants to draw on the nutrients in the soil, especially nitrogen, calcium, and magnesium, more readily. Seeds germinate more quickly. Plants grow faster and stronger, often maturing earlier with substantially higher yields than in unsolarized soil. The reason why is that the soil becomes almost "virgin", that is whatever had been growing in it has been destroyed or driven off so your garden vegetables or plants have a significant amount of time to establish themselves without competition from insects or weeds in their garden plot. 

How to Solarize Soil

The area to be solarized should be level and free of debris and large clods of soil. The soil should be watered if dry, but not saturated. The soil should have the crumbly damp look that the soil would have prior to regular planting. Place clear plastic over the soil surface and bury the edges in a foot deep trench. The plastic can be clear construction grade plastic and vary in thickness from 1 to 6 mils. The thinner plastic (1-2 mils) will allow better soil heating since it will reflect less solar energy. The plastic should be left in place for 2-6 weeks. Solarization is most effective when done in June, July, or the first couple weeks of August. This will allow you to begin your vegetable garden at the end of August or first weeks of September.