Let the Sun do the Work How to Solarize Your Garden Soil

Sun and clouds

Using the Sun to Sterilize Your Soil

The Sun. The center of our solar system, without which we would not be here. Sometimes all we modern gardeners can do is complain about how hot the sun is but early man worshiped the sun as a god and as a giver of life. In some respects, he was not wrong. Modern man has long recognized the important role the sun plays in our world and thus has attempted to use the sun’s power to his own end. This is often easier said than done. For a long time, the best I ever achieved was focusing the rays of the sun with a magnifying glass to burn holes in paper! Not too great a use I admit.

Plants are unique in that through the process of photosynthesis they can actually harvest the sun’s energy and use it to make food. We gardeners can also harness the sun’s powerful energy to help us in our gardening efforts. There is at least one good thing about our sometimes oppressive summer heat – you can put it to work for you by solarizing your garden soil.

Video: Prepare Garden Beds the Easy Way with Solarization

The Basics of Solarization

Solarization is a simple method to reduce harmful soil organisms, like weeds, nematodes, insects and soil-borne diseases, which will help your vegetables and flowers grow and produce better. The thing is that solarization requires heating the soil to a high temperature and then maintaining that temperature. Therefore, soil solarization is best done during the middle of summer.

Interestingly, research has shown that increased vegetable yields gained by solarization are greater than what would be expected from just destroying insect and disease-causing pests. While no one is quite sure exactly why this is true, results consistently show increased yields. There is evidence that the solarization process makes nitrogen more readily available to plants which could account for some of the increased yields. Also, beneficial soil organisms can be favored by solarization and tend to ‘bounce back’ faster than do the more harmful organisms.

How to Solarize Your Garden Soil

So how do you solarize your garden? The wonderful thing is that is very easy to do!

First you must understand that the process works by simply trapping the heat of the sun under clear plastic to pasteurize the upper layer of the soil where most of your plant’s roots are located.

To solarize your garden or flower bed, first prepare the soil. Eliminate as many weeds and old garden plants as you possibly can – bare soil is what we are after. Next, turn or till the soil as deeply as possible to produce a uniform soil texture. If your soil is too dry to easily work, water it deeply, wait a few days and then turn or till.

For solarization to work, the soil needs to be moist and damp to allow the sun’s heat to penetrate the ground as deeply as possible. So, give the area a good soaking before covering it with plastic. The plastic used to cover the area should be clear, not black. Clear plastic lets light energy pass through and then traps it, much like a greenhouse. Black plastic absorbs most of the sun’s heat without letting it pass through to the soil below. 1-to-6 mil plastic will work fine but keep in mind that in this case the thicker the better. Pull the plastic tight and cover the edges with soil or stone to help keep the soil moist and to prevent strong gusts of wind from blowing it away.

Leave the plastic in place for at least a month and the longer you leave it on the better the results. Two to three months would be ideal, but good short term weed control can be gained in a month. The soil in the top several inches should heat almost to 150 degrees F. which is hot enough to pasteurize the soil and kill many of the harmful organisms. Remember that the beneficial soil organisms do tend to bounce back quickly and are not greatly harmed by the treatment.

Read more: Weeds – What They Tell Us and Why You Should Care

Maintain Your Solarized Soil

After a month or so, uncover the soil, water, turn it (if you must) and plant! Planting as soon as the process is complete is best, any delay might allow a few stray weed seeds to blow onto the newly prepared area where they would happily take root!

That’s all there is to it! You do a small amount of work up front which allows you to harness the power of the sun to make your garden a much better place for your plants!

Happy Gardening!


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Joe Urbach


Joe Urbach is the creator/publisher of www.GardeningAustin.com and the popular Phytonutrient Blog. He has lived and worked in the Central Texas area for over 30 years. Joe is a certified Texas Master Gardener and is currently serving as the Director of Training for the Hays County Chapter of the Texas Master Gardener Association. He teaches and lectures on gardening regularly and can often be found speaking at local nurseries, libraries, garden clubs and extension offices. Joe has become a phytonutrient gardener and wants us all to come along for the journey to a better, healthier, longer and much more active and productive life!

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  • Profile photo of Hunter

    Wow! this contradicts everything I’ve ever learned about gardening. So if I kill everything in the soil then only the good stuff will come back right? what about no-till gardening?

  • I’ve heard about solarization before, but was concerned about harm to microbes. I am glad to hear that it might not harm them much. I would like to see more research on this. I was fascinated by the fact that crops seem to grow better after solarization. I’m sure we will see more studies being done. In the mean time, I will try solarization and occultation on a small scale, and learn as I go. Thanks for the good information!

  • Roy

    Not sure about this. Doesn’t seem to follow nature’s way of doing things. Seems a bit extreme and artificial.

  • Bob

    I have to agree with Mr. Urbach and I would like to read more of his teachings. My first question and only question at this
    time is what about earth worms? Does the soil get so hot that it will drive the worms off or just cook them? Out here in West Texas the soil (mostly clay) gets very hard and dry. I would like to think that they would go deeper, but I am not for sure how they would do. Any comments or thoughts. Bob

  • Marga

    And what about BPA and other harmful substances that are in plastic ?

  • con

    Depending on your latitude, using clear plastic may not be the best choice – at least from my experience… if the soil doesn’t heat up enough to kill the extensive root systems of some of the more pervasive perennial grasses (IE – Elymus repens, commonly known as couch grass) they will only come back more vigorous than before and without any competition – whatever you seed in the area will be quickly choked out if ANY roots of these “super-weeds’ remain viable. Sometimes it is best to ‘solarize’ with BLACK plastic which will kill even these weeds by preventing photosynthesis. THEN you can use the CLEAR plastic to heat things up – which will kill the seeds and eliminate pathogenic organisms. Also – making sure that there is PLENTY of soil moisture is paramount to the success of both of these methods. The water (and water vapor) helps trap and distribute the heat. If things dry out some of the tougher seeds will simply go dormant and wait for ‘better times’ – some seeds can remain viable in the soil for up to 50 years, while others can withstand extreme temperatures. The moisture and heat encourages germination (at least initially) and the lack of sunlight (under black plastic) or extreme heat (under clear plastic where the sun is in the right place to create this effect) will do the rest.

  • Linda Morrison

    After reading your article and explanations, I clicked on the video you recommend about solarizing your soil. The link took me to another article and video by Marjorie Wildcraft, which gives recommendations EXACTLY CONTRARY to the ones in your article. (She says NO LIGHT on the plants, cover the area with a tarp or black plastic.) I´m sorry, but if your information is contradicted by that in your link, it is NOT AT ALL HELPFUL for my understanding. I would appreciate a clarification.

  • Deb

    I tried the clear plastic one year in northern Montana and it acted like a greenhouse, supercharging all the weeds underneath. I only use sturdy, black plastic now when I do it.

  • Profile photo of David Clark

    would be nice if the video link went to where it says its going, ie Prepare Garden Beds the Easy Way with Solarization, instead of going to Homesteading Basics: How to Prepare a Garden Bed with a Bad Back????

    Maybe you can put the correct link in please.

    Regards David

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