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Paul Underhill  |  Terra Firma Farm  |  Winters, CA

Subject: Solarization

I'm wondering if anyone out there has tried or is successfully doing soil solarization for weed control?

I did a few small fields this year and am hoping to compare notes on challenges and strategies. As usual, the resources available from UC extension are very academic in their focus and offer very little practical information and zero problemsolving details.

Thanks!

In Topics Pest & Disease Management

In General FarmsReach community

Comments 12
08/01/17
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  |  Heavy Dirt CSA  |  Davis, CA commented

I got used plastic so can't tell you the exact specs since I didn't buy it new. My understanding is that it was made specifically for solarizing, and the farmer I got it from (UCD student farm) got it second hand from a wildlands reclamation program where it was used to control invasive weeds / clear house before planting natives. It is substantially thinner than greenhouse plastic, but sinilarly UV stabilized. Because it was used and had a few holes, we doubled it over, and after soaking the area, covered up the THICK stand of Bermuda for 2-3 months of summer heat. Once or twice, I threaded a hose into the patch under the plastic and soaked it again. When I pulled it back in October or so it was truly a miracle! A thick mat of dead Bermuda mulch and not a rhizome to be found.

A couple of things of note: we have EXTREMELY heavy clay soil, which I've heard keeps Bermuda rhizomes quite shallow, helping

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08/05/17 9:55 PM
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  |  Page's Organics  |  Ramona, CA commented

Sarah...What type of used plastic worked on Bermuda?

08/05/17 7:08 PM
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  |  Terra Firma Farm  |  Winters, CA commented

Good to know. I'm using 60" plastic on 60" beds but after pulling off the plastic I only have about 34" of solarized bed top to plant into. Apparently I need to tweak my mulch layer, or maybe use narrower plastic.

Having talked to Tom Willey it does seem like solarization is easier to do on bigger beds. He's on 38" beds but combined 2 beds into one 76" bed when he was solarizing.

08/05/17 5:53 PM
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  |  Kings River Produce, Inc.  |  Hanford, CA commented

Paul I haven't had that problem before. We use 74" clear plastic on an 80" bed which is about 64" across the top of the bed.

08/04/17 6:25 PM
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  |  Terra Firma Farm  |  Winters, CA commented

Hi Steve, thanks for chiming in. That's what we are doing but it's filling the furrows in completely and then I am having to re-furrow, which is pushing weedy soil back onto the beds. I think one of my problems is that I don't have enough room on my 60" beds to keep the solarized 33" bed top from getting "contaminated" by the unsolarized soil from the furrows.

I may have to adjust my planter (3 rows) so that the outer planters are further away from the furrows.

08/04/17 1:46 PM
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  |  Kings River Produce, Inc.  |  Hanford, CA commented

Split the plastic down the middle with a coulter blade and pull it from the center, that way the non-solarized soil stays in the furrow. We solarize roughly 150 acres per year and that system works well for us.C2A0
08/02/17 10:03 AM
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  |  Terra Firma Farm  |  Winters, CA commented

All roads are leading me to Tom Willey, sent him an email thanks. Because of the scale I am doing it on, I am using my plastic mulch layer on beds. Everything worked great until I went to start pulling the plastic off which ended up both filling my furrows and throwing a certain amount of unsolarized soil back up onto the beds partially defeating the purpose. Bed tops are super clean but there are weeds growing along the edges and furrows and when we cultivate those it throws more soil up onto the beds.

08/02/17 9:27 AM
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  |  Organic Ag Advisors  |  No. San Juan, CA commented

Paul, Talk with Tom Willey. He has the mist experience with solarization of any one I've talked to. He really used it a lot.

08/02/17 8:03 AM
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  |  Our Table Cooperative  |  Sherwood, OR commented

You will want to use thick plastic, 4 mil or greater, it will hold up better to the wind and sun, and if wind is still an issue might be best to bury edges. Old greenhouse plastic works well. You want to get the soil to 140 degrees or higher to kill weed seeds and pathogens in the top of the soil, and will have bests results in the height of the summer with 4-6 weeks. It's a long time but a good bare fallow for the winter or following year. In the north, growers will solarize with two layers of plastic to get the soil warm enough- one is your greenhouse structure buttoned up and the other a sheet of plastic on the ground inside the greenhouse. Hope that helps!

08/02/17 2:57 AM
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  |  Ananda Valley Farm  |  Half Moon Bay, CA commented

Tried using plastic tarps to suppress weeds this year as a trial, motivated by "New Market Gardener" methods.

For clear plastic the weeds kept growing and liked the warmth.

Mix results with black plastic left on the ground for 4-5 weeks.

Had plastic on the ground in early spring.

The black plastic was quite effective at eliminating grass weeds.

But once it warmed up after planting, the amaranth all sprouted and other warm weather weeds did (not grass though).

Maybe if you also kept plastic on through June and then removed it, if you don't have beds that need to be in production earlier.

Another issue was wind, we are in a windy area and sandbags were not enough to keep them from flying away, needed 2-3 pallets for just a 20'x100' piece of plastic.

Also they attracted gophers, which loved the warm soil.

Did one bed on a "pasture", a field that had been grass for over a decade. Just put plastic

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08/01/17 11:43 AM
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  |  Jellicles Farm  |  Sunol , CA commented

I tried both solarization using clear plastic and also the other one using silage tarp. The plastic makes me nervous. needs to be disposed asap..can disintegrate. You need to water before you lay it down. Staples suck. But only choice. the hottest time of the year is alReady past. But it does work on most annual weeds. Soil cracked in some places. I feel like maybe munching is better? I like the idea of it..the concept is solid. Plastic, no good. There is another way using landscape fabric. It's not sokarizatiob. It's breatheae and UV resistant. Long life. That is better imo.

08/01/17 11:31 AM
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  |  Heavy Dirt CSA  |  Davis, CA commented

I got some used plastic from Raoul at the UCD students farm who said he uses it primarily in preparation for fall carrots. I used it on a patch of Bermuda grass with great results (2-3 months covered through summer heat after a deep soaking) which although might not be applicable for you is a pretty awesome discovery for home gardeners and market growers. I recently heard from Tyler at Soil Born that Tom Willey was giving him some pointers because, presumably, he has some experience. So that might be a good olace to start for your scale....although not sure how available Tom is these days since I think they're retired last year?

08/01/17 11:26 AM

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