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Past Articles Library | Organic Weed Killer | Soil Solarization


Yes! This technique can be modified for cooler times of the year and cooler climates which we will be talking about, but before that, let's go over the basic idea of solarization.

Basic Overview:

One of the best nonchemical ways to get rid weeds, and some diseases and pests, is to solarize your soil.

While normally this technique is used in areas with lots of sun and high temperatures, it can be modified for cooler areas and for cooler times of the year.

The results may not be as long lasting or effective, but it can sure help if you are having a battle against weeds.

Solarization is a simple nonchemical technique that captures the radiant heat and energy from the sun and causes physical, chemical, and biological changes in the soil. These changes lead to control, or suppression, of soilborne plant pathogens such as fungi, bacteria, nematodes, and pests along with weed seeds and seedlings.

Solarization consists of covering the soil with a clear plastic tarp for 4 to 6 weeks during a hot period of the year when the soil will receive maximum direct sunlight. When properly done, the top 6 inches (15 cm) soil will heat up to as high as 125° F (52 ° C).

Over several weeks, that's hot enough to kill a wide range of soil inhabiting pests such as; wilt and root rot fungi, root knot nematodes and noxious weed seed.

In addition, solarization stimulates the release of nutrients from organic matter present in the soil. It is especially effective for treating garden soils, where the intent is to plant vegetables, herbs, and flowers.


Now I have used this technique, with very good results, during the fall and winter months.

Don't always listen to the so called "experts" that tell you this can only be done during warm weather, because I have personally tested this in the fall and winter and it works great.

You may have to leave the plastic on a bit longer, and you will only kill weeds and some weed seeds in the most upper level of the soil surface, because the soil won't get hot enough to kill soilborne diseases and pests, but if you want to clear weeds out the easy way, it will work!

Note: Never be afraid to test techniques for your own purposes!

How to Solarize Soil Normally and With Modifications

  • The area to be solarized should be free of debris and large dirt clods

  • If you have clods, till the area to be treated. It is necessary to break up soil clods and plant debris in order to enhance heat conduction through the soil. The soil surface should be raked smooth before covering with plastic. A fine soil surface will allow the plastic covering to be placed in close contact with the soil, with few air pockets to interfere with direct solar heating

    • Modification:
      If you have a weedy area that is out of control, or grass that is hard to get rid of even with tilling, cut down the weeds and get rid of the grass as best you can, and then proceed with the next steps

  • The soil should be moistened if dry, but not saturated. Wet soil conducts heat better that dry soil, so it should have a crumbly damp look to it, like it would at planting time

  • Place clear plastic over the soil surface and bury the edges, or place bricks or heavy objects on the edges, to keep the plastic in place and from blowing away

    • Modification:
      Many people always recommend using clear plastic because the idea is that clear plastic produces higher temperatures faster because the sunlight passes through the clear plastic to heat the soil. While this is true, if you are in a cooler climate or a cooler time of the year, I have found that black plastic works just as well because it absorbs the heat making it quite hot. The soil surface near this hot plastic gets quite warm, which as stated above, may not be hot enough to kill diseases or some weed seeds, but it will clear the area nicely of weeds and some seeds.

      I know that the black color can intercept the light, and some heat can be lost to the outside air, but try it.

  • 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

  • Large sheets of plastic to use for solarization are available at hardware and home supply stores

  • The plastic should be left in place for 4-6 weeks

    • Modification:
      In cooler temperatures, leave on for 8-10 weeks

  • True solarization is most effective when done during the hottest time of the year, which for some people is in June - July, or depending on your geographic location, May, August, and September.

    That said, do try it during other times of the year and see how it works for you, because I have, and have found it a very useful aid in weed control.
Overall, solarization is by far, the most effective way home gardeners have to reduce or eliminate soil-borne garden pests. Plus, it allows you the flexability to put the plastic down in any area that is giving you problems. The tangible benefits: healthier and more productive flower and vegetable gardens!


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