What Is Soil Solarization?

“I’ve heard that you can use solar energy instead of chemicals to control some soil diseases and pests. How can I do this at home?”

For many of us, it’s hard to get motivated to do garden work during the heat and humidity of an Alabama summer. But you can put that heat to work for you in your garden.

You can get rid of many harmful diseases and weed seeds in your garden soil using the sun’s heat in a process called soil solarization. Solarization involves spreading a sheet of clear plastic over moistened garden soil and trapping the sun’s energy. This will raise the soil temperature high enough to kill many disease pathogens, nematodes and weed seeds. With the loss of fumigants and soil sterilizing chemicals, this is a viable alternative for homeowners with nematodes and soil diseases.

Soil temperatures can be raised to 120 degrees Fahrenheit or higher in as little as four to six weeks during summer in Alabama. The longer you leave the clear plastic tarp in place the deeper the penetration effects will be and the more increased control of pests you will achieve.

what is soil solarization?

Garden soil covered for solarization.
Photo Courtesy of Hunter McBrayer, Alabama Extension

Many vegetable gardeners don’t want to give up planting space, so plan to solarize an area where a summer crop has just finished. For example if you’ve finished harvesting bush beans, pull up the plants and solarize that area.

To gain the maximum benefit from solarizing your soil, follow these guidelines:

  • First, remove all weeds and plant debris from the area.
  • Then till or use a fork to break up the soil bed. Rake the soil to remove rocks or dirt clods and to smooth the surface. A smooth soil surface will allow close contact between the soil and the plastic.
  • Water the soil evenly to a depth of at least 12 inches.
  • Bury the edges of your plastic about 5 to 6 inches deep all the way around the plot. This seals in the heat and prevents the plastic from blowing or tearing.

Solarization is most effective with clear plastic. Select a 2 or 4 mil plastic because it is less likely to tear or puncture. Leave the plastic tarp in place for at least 4 weeks. You can monitor soil temperature periodically, but be sure to secure the plastic back in place snugly for an airtight seal.

After removing the plastic, avoid deep cultivation to prevent bringing up more viable weed seeds. The plot is ready to be planted with seeds or transplants. Fall garden crops will get an excellent start without competition from weed seeds and diseases.

Solarization not only saves money that would otherwise be spent on herbicides and pest control products, but it may also help increase the number of beneficial bacteria and fungi in your soil.

By Bethany O’Rear, Regional Extension Agent, Alabama Cooperative Extension System.  Contact Bethany at bethany@aces.edu.

The Alabama Cooperative Extension System (ACES) operates as the primary outreach organization for the land-grant functions of Alabama A&M and Auburn Universities. ACES is committed to affirmative action, equal opportunity and the diversity of its workforce.  Educational programs of ACES serve all people regardless of race, color, age, sex, religion, disability, sexual orientation, or national origin.

Alabama Extension

The Alabama Cooperative Extension System operates as the primary outreach organization for the land-grant functions of Alabama A&M and Auburn Universities and answers home-gardeners' questions each week on Birmingham Gardening Today.

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