I wrote in August 2019 about Solarization and Crop Choices to Fight Nematodes. Previously we solarized part of a bed in our hoophouse, or one or two beds. I’ve written before about our first efforts at solarization to fight root knot nematodes in our hoophouse. Back then we shoveled soil on the plastic edges to make a good seal between the plastic and the soil. Later we developed a good technique of pushing the plastic edges down into soil using spades, which gives a much better seal, and if you work both sides of the bed at the same time you can avoid wrinkles.

This summer we decided to solarize the whole hoophouse. We hope to make progress on reducing fungal diseases in our winter crops, drawing down the weed seed bank, and killing lots of nematodes. We plan to solarize for the whole of August (4 weeks). Here’s the story so far.

Solarization

Solarization is a method of killing pests, diseases and weed seeds near the surface of the soil by covering the soil with clear plastic in hot weather. Nematodes are only active in warm weather, and we have not had problems with them outdoors, but of course, it’s warmer in the hoophouse!

In my Book Review: The Organic No-Till Farming Revolution: High Production Methods for Small-Scale Farmers, Andrew Mefferd, I wrote a little about solarizing:

“Solarization uses clear plastic (old hoophouse plastic is ideal). In a summer hoophouse, solarization can be as quick as 24 hours, Andrew says. When we’ve done this, one of our goals was to kill nematodes and fungal diseases, not just weeds, so we waited a few weeks. Outdoors it takes several weeks. You can see when the weeds are dead. Bryan O’Hara poked a thermometer probe through solarization plastic and found a 50F degree (28C) difference between the outside air and the soil immediately under the plastic; a 10F (6C) difference at 1″(2.5 cm) deep and little temperature gain lower than that. Solarization does not kill all the soil life!”

Preparation for Solarizing

Last time we changed the plastic, we saved our old hoophouse plastic in one large sheet, for just this option of solarizing the whole hoophouse. Unfortunately, someone used it for some other purpose, and we ended up having to buy new plastic to carry out our plan. Ouch! Label your old plastic very thoroughly! We bought 4 mil Tufflite Nursery Clear plastic from Nolts Greenhouse Supplies, Ephrata, PA (only rated for one year outdoors), thinner than the 6mil we buy for covering the frame. Be aware that shipping can be a big part of the cost, unless you are ordering lots of things.

We pulled up our tomatoes and cucumbers at the end of July, a week earlier than usual. The squash had already gone. I was sad to say goodbye to the bell peppers as they were the best we’ve had in years. Usually we keep the peppers until October and do our winter crop planning so that the pepper area is the last planted in winter crops, but we made that sacrifice! For several years our peppers didn’t do well, as the salinity of our soil had got too high. We now do salt wash-downs in September and March. This year they were spectacular! Big plants, huge peppers!

We decided to keep the big shadecloth in place for the solarizing day, expecting it to be very hot. It wasn’t, but it was a wise precaution. We planned to remove the shadecloth the next day, but it was raining and we need the shadecloth to be dry to pack it away. So we waited a couple of days for our little monsoon season to pass. Normally we leave the shadecloth in place until mid-September or so, but this year we want maximum heating for the solarization.

We are leaving the drip tape in place so we can water the soil and keep it alive below the hot zone. If we had thought of it in time, we might have spread compost on the beds before spreading the plastic and killed the weed seeds that have landed on the compost pile while we ignored it since early April. We were stretched thin and got behind with the mowing, and we know grass and spiny amaranth seeded somewhat on to the pile. We did have it partly covered with a tarp.

Unrolling the Plastic

We bought plastic 32’x100’ which was just right for the footprint of our 30’x 96’ gothic hoophouse. We unrolled it down the center bed (it was folded in several concertina folds from each edge to the middle). We gradually unpacked the folds and pulled the plastic out to the edges. It is important to get as smooth and tight a fit as possible (few airgaps between soil and plastic).

We designated one person to take their sandals off and walk on top of the plastic, while the rest of us gathered small buckets and put some rocks in them, to anchor the edges. This all went very smoothly and took less time than we expected. We used about one bucket of rocks every 20’ down the length. We rolled our painters’ pole that we use for our SnoBrum in the plastic across the west doorway, the direction the strongest winds come from, for add extra security in preventing wind getting under that edge of the plastic. We did not bury the plastic edges in the soil, as that seemed difficult and we figured a large area would suffer less edge cooling/heat escape than a single bed.

Closing Up the Hoophouse for a Month

We closed the doors and windows and relaxed into enjoying a summer month off from harvesting in the hoophouse. We have made a list of infrastructure repairs, landscape care and, of course, the winter crop planning to do in t he next month. And we’ll be irrigating maybe twice a week and checking the soil thermometer periodically. It showed 80F last week, before we solarized.

More Resources on Solarizing

eOrganic’s Organic Vegetable Production Systems Topics list offers publications on plant disease management, weed management and management of soil-borne pathogens using Anaerobic Soil Disinfestation. Here’s a 2025 webinar about On-farm Anaerobic Soil Disinfestation for the Management of Soilborne Pathogens in High Tunnel Production Systems:

 

https://www.youtube.com/watch?v=2pEf26ae6XI

The University of California Solarization site and their Small and Organic Farm Advisor have good information, including some in Spanish and Hmong

More Resources on Nematodes

I’ve written here before about our struggles with root knot nematodes in our hoophouse, and you can read everything I know about nematodes in the Year-Round Hoophouse.

My article on nematodes in Growing for Market  in November 2014 describes our discovery of the beasties and our first attempts to deal with them. My most thorough blogpost about nematodes was for Mother Earth News  Managing Nematodes in the Hoophouse. It’s free for MEN members.

There is info on dealing with nematodes from Garry Ross in Hawaii, where nematodes are a fact of daily life, in my post Cold weather, snow, thinking about nematodes from February 2015.