More on Soil Solarization: How to Kill Those Germs

August 14, 2014

Instead of “reinventing the wheel”, I am going to list the steps to follow in order to solarize your soil. At the end of this post, you will find links to two very good resource guides from UC Davis, Division of Agriculture & Natural Resources that will provide you with in-depth information, the how-tos and the whys of soil solarization: the first guide is available through the mail for $5.00, and the other guide can be viewed on-line and downloaded for free. The download also includes a nice section on how to solarize containers, which is very helpful if you garden in containers, rather than in beds.

So, there are basically four steps to solarizing:

Prepare the soil for planting by removing the plant matter.

Level the soil and rake away clods, litter and air pockets. Air pockets reduce the temperature and also keep the plastic from “adhering” to the soil.

Wet soil immediately before laying down the tarp. Wet soil helps conduct heat.

When solarizing only the bed tops, it is best to apply water under the tarp with a drip system. Otherwise, the uncovered furrows will become weedy and special care will be required to keep plant parts out of the treated areas during weed removal.

Roll tarps over the surface, smoothing out air pockets.

Bury the edges of the tarp with soil. Strips may be placed so only the tops of planting beds are covered and furrows are left untreated.

After solarization is finished, remove the tarp before planting. Tarps may be left on the soil and serve as a mulch for the crop by transplanting plants through the plastic, however, doing so may make conditions too hot for some plants, such as asparagus. (I am not a fan of leaving the tarp in place because I don’t want the plastic to break down and get into the soil.)

Do not leave the tarp on for more than 6 to 7 weeks, or it will become brittle and difficult to remove.

Use clear polyethylene plastic tarp 1 mil (0.001 inch [0.025 mm]) thick. Thicker tarps, 1.5 to 2 mils (0.038 – 0.050 mm), can be used in windy areas (avoid thicker 4 to 6 mils as they are more reflective and don’t allow the soil to heat up as much)

So, those are the basics. Now, for the extended versions, view the Resources: Soil Solarization: A Nonpesticidal Method for Controlling Diseases, Nematodes, and Weeds, UC ANR Publication 21377 for $5.00; Soil Solarization for Garden & Landscapes, Pest Note No. 74145, for free.