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Commercial Fruit and Vegetable Growers

From Dixon Springs Ag Center: High tunnel cover crop solarization

rows of green plants inside high tunnel with sections covered in clear plastic

Vegetable transplants are growing well in the greenhouse and should be ready for planting within our high tunnels in the next 2 to 3 weeks. Peaches are in bloom and the summer apple variety in my front yard was at tight cluster. In partnership with our local high school FFA clubs, we hosted another successful year of horticulture and ag business management contests, giving the students an opportunity to see ongoing applied research projects on site.

On February 27, we covered half of the cover crop plots within our high tunnel with clear 2 ml plastic to begin the solarization process for terminating the cover crops. The other half of the plots will be terminated using the mechanical method of weed eating once the crops show signs of flowering. The cover crops planted in the plots include annual ryegrass/crimson clover, annual ryegrass/Austrian winter peas, spring oats/crimson clover, and spring oats/Austrian winter peas. The spring oats never did winter kill this year. We did not get a good stand of crimson clover, but the few plants in the uncovered plots are beginning to flower as of March 25, which is the same timeline as last year. Hopefully, the annual ryegrass and spring oats will begin to show signs of flowering within the next week to keep us on track for setting out tomato and pepper transplants by April 10 at the latest. If the plants haven’t reached the physiological stage of reproduction (flowering) at the time of termination, the risk of cover crop regrowth is higher.   

After one month of being covered in clear plastic, most of the annual ryegrass appears to be “cooked” but the spring oats are proving to be tougher, with a fair amount of green still present. The few areas with crimson clover still appear to be quite green under the plastic. Currently, our plan is to remove the plastic next week and do an assessment of insects present in all plots and do a rating of termination effectiveness via solarization.

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person working inside high tunnel pushing down row of green plants
Plants in the plots to be solarized were stamped down to make plastic covering easier. The pressure on the plants was not enough to crimp or break stems. Photo credit: B. Aly, Illinois Extension 2025.
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person leaning over stapling clear plastic over bed of green plants
Clear plastic sheeting was stretched and stapled over the plot areas to hold in the heat generated from the solarization process. The ends of the plots were also sealed with dirt. Photo credit: B. Aly, Illinois Extension 2025.
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rows of green plants growing inside a high tunnel with sections of dead plants covered in clear plastic
One month after plastic was put down over cover crop plots for solarization termination. The remaining cover crop plots have been actively growing within the high tunnel and will hopefully be nearing flowering soon. Photo: B. Aly, Illinois Extension 2025
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outside of high tunnel structure with clear plastic getting attached
Ropes were tied to one long edge of the plastic in preparation for pulling it up and over the high tunnel frame. This roll of 6 mil plastic was 42 ft by 100 ft. Photo credit: B. Aly, Illinois Extension 2025.

Over the weekend of March 15, our region experienced strong storms that caused structural damage in several areas. The plastic on one of our high tunnels was ripped off during this event and fortunately there was no damage to the frame or the other tunnels on site. This plastic was already scheduled to be replaced this year as it was 11 years old and the original plastic from when the tunnel was first put up in 2014. It was amazing that the plastic had held up so long as normal life expectancy is usually 3 to 4 years. We were lucky to have a 4-hour window with no wind on March 17 and had the tunnel reskinned within 2 hours. Already having the roll of plastic on hand allowed us to capitalize on the calm weather as the wind has been blowing non-stop for the past week and a half.