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Brown Golding Lettuce in a Low Tunnel
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Using Low Tunnels For Season Extension

Extending The Growing Season With Cold Hardy Vegetable Varieties and Low Tunnels in McLean County, Illinois

A lot of research has been done on season extension for market farmers, but there is little data available from central Illinois farms. Low tunnels offer a very flexible low cost way to provide a protected growing environment to crops. These structures can extend the fall and winter harvest season for greens and with the right succession planting schedule offer earlier harvests in the spring. There is potential to direct seed a crop like Walla Walla onions in late summer and protect them through the winter allowing a harvest of full size bulbs 4-5 weeks earlier than spring planted onions. It may also be possible to direct seed in the winter and cover the soil with a low tunnel to get plants like carrots, onions, peas, etc to germinate very early in the spring and get a jump on the season. I am using a low tunnel to test the cold hardiness and eating quality of a variety of cold hardy crops over the winter of 2013/2014.

I planted a mix of cold hardy crops starting on August 23rd and ending on September 28th. Some varieties are newly created farmer bred varieties that have been selected for cold hardiness and have the ability to survive lower winter temperatures than the standard varieties offered by most seed companies. I covered the crops with a low tunnel to test winter hardiness and eating quality of a range of vegetables over the winter. The goal is to collect central Illinois specific data on planting dates, winter survival, eating quality, and the performance of different crops and varieties.

I purchased a quickhoops bender from Johnny's Seeds and built a low tunnel using ½" EMT conduit. I covered the tunnel with Agribon 19 fabric on November 9th. I added a layer of greenhouse poly on November 23. I crossed a rope over the tunnel by threading it through a 9 gauge wire staple at the base of every other hoop on alternating sides. I also put bricks and bags of rocks on the plastic. The biggest challenge so far has been keeping the plastic on the hoops. If you live in a windy area be sure to use a lot of heavy objects to hold the plastic down.

Other farmers have found that low tunnels tend to average 5 degrees of protection to crops under moderate conditions and the amount of protection increases when temperatures drop to extreme lows. I have observed similar results in my low tunnel. On November 10th and 11th the nighttime low temperature was 18 degrees and the low temperature inside the tunnel was 27 degrees. When the sun shines the temperature inside the tunnel rises into the 60's during the day when outside temperatures are in the 30's.

The combination of warmer temperatures and no wind has resulted in continued growth and high quality greens. On November 26th the outside temperature dropped to 11 degrees and the temperature inside the tunnel was 21 degrees. The low of 21degrees did slight damage to some of the outer leaves of the greens, but most greens are still thriving and the inner leaves are still edible and could be sold to winter CSA customers or other winter marketing outlets. I plan to monitor and report on the condition of these crops from now through March.

Planting dates for low tunnel crops.

August 23rd

Evergreen Hardy White Onion

Vates Kale

Aprovecho hardy Turnip (Adaptive Seeds)


Tres Fine Endive

Keystone Endive

Manoa Lettuce (Wild Garden Seed)

Brown Goldring Lettuce (Wild Garden Seeds)

August 26

Cornet De Bordeaux Escarole (Adaptive Seeds)

Pokey Joe Cilantro (Adaptive Seeds)

September 6


Pokey Joe Cilantro

Cornet De Bordeaux Escarole

Brown Goldring Lettuce

Manoa Lettuce (Adaptive Seeds)

Briweri Lettuce (Adaptive Seeds)

September 13

Winter Density Lettuce

Winter Marvel Lettuce

Brown Goldring Lettuce

North Pole Lettuce

Rouge D'hiver Lettuce

Chinese Thick Stem Mustard (Even Star Farms)

Even Star Tatsoi (Even Star Farms)

Even Star Winter Arugula(Even Star Farms)

Vit Mache


September 18

Vit Mache


Even Star Winter Arugula (Even Star Farms)

September 28

Vit Mache

Seed Sources: Johnny's Seeds, Fedco Seeds, Wild Garden Seeds, Adaptive Seeds.


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