Dirty Business: Solarizing

No, this is not science fiction

No, this is not my garden.

One day, while perusing Rodale’s Garden Problem Solver to look up a tomato plant disease, I came across a brief explanation of solarizing.  This is essentially a natural means of pasteurizing the soil to kill off many of the things that cause so many problems. 

Once upon a time, it was thought that certain plant diseases simply could not be addressed once they took hold in the soil.  At some point in the…1980’s I think, this technique was developed in Israel and has been tested enough times over the years that it is now a generally accepted technique for conditioning the soil to kill off those diseases, plus weed seeds and certain pests.  The funny thing to me is that, even though I can do a search for “solarizing” and get a whole slew of hits, it’s still not really a household name so not universally known.  There are lots of sources out there which can likely provide better detail, but here’s a decent primer.

The best time to solarize the soil is during the hottest period of the summer—so, depending on where you are, can be anywhere from July through early September.  July here was surprisingly cool, so it’s a good thing that I decided to start at the beginning of August, right when the temperatures have started to spike again.  Here’s the basic process:

  • Make sure your bed is completely cleaned of plants and weeds.
I moved the butternut vines up one level to get them out of the way while I did this. The soaker hoses will be pulled out, then put back in.
  • Loosen up the top foot or so of soil with a pitchfork, or tiller.
  • Water the soil heavily so that it is completely soaked.  Much wetter than a regular watering.  Basically, you want to make mud.  Then let the bed sit overnight.
  • The next day, cover the bed with clear plastic sheeting—anywhere from 3 to 6 mils thick.  Do not use black plastic because it will not produce the necessary greenhouse effect. I used a 4 mil sheet.
  • In most gardens, the final step would be sealing the plastic sheeting by covering the perimeter with soil.  However, that’s impractical for our landscaped garden beds, so I seal the edges with mason block caps.

Then, for my part, I moved the butternut squash vines back to their earlier place, across the now-prepped bed and into the peppers.  I can’t leave them where they are, because I need to walk on that area to tend to the tomatoes. I also can’t just lay them down on the plastic because they will shade the soil and make this whole effort pointless.

I found more caps after I took this picture, so now they are lined up end to end.

The plastic will stay in place for four to six weeks.  During that period it will rain, so I will need to use a broom to sweep the water off of the plastic, otherwise the pooling water will reduce the greenhouse effect.

With the high humidity under the plastic, combined with direct sunlight, the soil temperature can get as hot as 140 degrees, which will kill off pathogens, shallow weed seeds and destructive nematodes.  One of the funny things about this process is that it does not appear to wipe out certain beneficial organisms, which means the bed will produce healthier, more robust plants.  The jury is still out on how long this treatment lasts, but some studies appear to suggest that a properly solarized bed can stay free of pathogens for up to five years.  Because we rotate our crops, and because the onions and garlic are harvested right around the time solarization is necessary, my plan is to solarize one bed every year, and then plant the tomatoes in that bed the following year because those are the plants that have the most trouble with disease.  We’ll see how it goes.

About butcherbakertoiletrymaker 557 Articles
When you can walk its length, and leave no trace, you will have learned.


  1. …I can remember having to help lay down plastic sheeting to help kill off weeds as part of prepping a vegetable patch at my grandparents’ place…but I can only aspire to the level of organization you seem to have

    …neat trick, though…might have to mention that one to some folks I know…& hope they didn’t just buy more black plastic sheeting?

    • It seems that using black plastic only has a superficial effect by killing anything already growing, but it doesn’t seem to have any effect on weed seeds that haven’t sprouted yet.  So, if your friends really want to wipe out the weeds, this should be a more effective method.

      • …it makes a lot of sense to me…pretty sure there wasn’t watering involved in the other version either so it was really just starving the surface of sunlight after it was dug over but prior to it being planted so anything that had been brought to the surface would knock it off & not get any ideas

        …seemed to do pretty well in terms of keeping the weeding requirements to a minimum…but the version you describe seems like it’d be vastly superior

        • Adding on to BBTM’s reply, 
          Iirc, the reason the Black plastic doesn’t work as well, is that some seeds only sprout after a “hot/cold cycle in darkness” (even an artificial one!) or they’ll stay dormant until after a stretch of darkness…(and this CAN include certain weeds, too!) 
          So, basically, if you prep a bed this way but use black plastic, instead of clear, you end up priming it *perfectly* for those particular “light-cycle dependent” weed seeds😉💖

          • Eta–this is *also* why it can be SO IMPORTANT, to make sure that if one is using any sort of “homemade greenhouse” made out of boards & old windows, you get it either moved to a spot you don’t care about, get it OPEN *every.single.day!* or you get the glass off it, well before that first hot stretch of late spring/early summer!
            Cuz you’re gonna KILL that bunch of baby plants, you just spent so much time & effort carefully starting!😉🙃
            (Been there DONE THAT, one particularly lazy early-June!😖😱🤣)
            Tbh, SAME with the baby tomato starts & plastic milk jug/pop bottle “cloches” that you kept the lids on!–forget for one hot-ish weekend, and they are DEAD!!!🤣 (did THAT a different year!😖😬🙃)

  2. Excellent process description! I already have a garden bed in mind.

  3. Excellent advice, as ALWAYS, BBTM!!
    I’m excited to read how it works out for you guys, and how the rotation goes!😉😁💖

  4. Hey so stupid question time because I legit just came inside from layering down black plastic sheeting to kill off grass so I can do a perennial bed planting in 2 months.

    I kept reading that black plastic was best for that purpose, did I just fuck that up? I’m not trying to kill off any soil pathogens, etc. I just wanted to get rid of grass without using any herbicides. The yard isn’t weedy because I just pull those when I see them. 

    • I guess it depends on whether your grass had ever gotten tall enough to go to seed over the season. If not then…maybe it’s OK? Of course there’s also the possibility of seeds from other weeds like dandelion or types of crab grass and whether those got in the ground and hadn’t sprouted yet. It’s a tough call no matter what. 

      • The grass hasn’t gotten tall enough to go to seed in the 3 years I’ve been here, so I think I’m good there.

        There might be some weeds break through, but also I was going to plant and then mulch and there’s always some maintenance anyways with weeding so I guess I’ll just see what happens!

    • Not at all the expert here, but this seems to me to be two different practices for two different goals.
      The “solarizing” thing in this post looks to me to be an attempt to make a mini-greenhouse to cook pathogens by raising the temperature enough to… idunno, denature their proteins or whatever.  I mean, it’s supposed to get up to 140F, and isn’t that pretty close to what we cook some food at?
      Whereas, I think what you are looking at is more at just trying to “clear some space”, and depriving the existing plants of light/air for a bit might be good enough…

      • This!!
        Also, the black plastic is sometimes used for grass-killing,because of the “heat absorption” factor😉
        If weed seeds *were* a major concern, Brighter could always “double up,” if there were enough time–black plastic for a couple weeks (till everything was dead), then clear-plastic greenhouse style, like Butcher is doing😉💖

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