Low Tunnel Giveaway to Increase Grower’s Knowledge of Season Extension
by Dan Phelps and Cole Cottin
This year, a total 1,300 feet of free low tunnel infrastructure was awarded to 13 specialty crop growers across Kansas as part of the Kansas Rural Center’s “Tunnel to Table” educational programming – to increase the number of growers experimenting with low tunnels, which put to work the same simple technology as high tunnels for a fraction of the price. Low tunnels can provide a cost-effective investment option for those seeking to begin or advance their use of protected growing systems on their farms.
In recent years high tunnels have gained popularity and abundance across the Kansas landscape, but the lesser-known low tunnel offers an alternative form of crop protection and season extension that may work even better for some growers and in certain situations.
How do low tunnels and high tunnels differ? Structurally, low tunnels are essentially miniature versions of high tunnels. However, unlike high tunnels, low tunnels are too short to walk in, are moved seasonally, and lack much of the structural support offered by high tunnels. Another major difference is that the plastic on a high tunnel is attached to the structure, whereas plastic on a low tunnel is weighted down on the ground.
The cost difference between high and low tunnels is significant. Whereas high tunnels using half inch metal pipes and six mil. greenhouse-grade plastic cost two to three dollars per square foot, low tunnels with the same pipes and plastic cost just 30 to 60 cents per square foot. The cost drops to as little as five cents per square foot if metal wire and row cover – a breathable poly- spun fabric – are used instead.
Low tunnels and high tunnels are also used a bit differently. Unlike high tunnels, these low cost structures can be dissembled, moved throughout the farm, and work with the contours of the land. Similar to high tunnels, low tunnels can provide crops with several degrees of cold protection at night but, due to their smaller stature, low tunnels heat up more rapidly during the day. In Kansas’ climate, low tunnels may be covered in plastic from late October or early November through late February or early March, at which point the operator will need to remove the plastic. This is because, similar to high tunnels, low tunnels need to be manually ventilated if temperatures near 70 degrees, as they occasionally do in late fall and early spring.
Low tunnels and high tunnels each have their own unique set of challenges. Because you can’t stand-up in low tunnels, you must partially remove the covering to access your crops which can make it difficult to harvest or weed in high wind, rain, snow, and sub-zero temperatures. Low tunnel construction and dismantling must be done annually and is labor intensive. Low tunnels are, of course, lighter, so Kansas farmers must take extra measures to ensure their low tunnel doesn’t end up in the neighbor’s tree line.
According to Johnny’s Selected Seeds – a company that sells low tunnel supplies and has done a lot to promote and advance the technology – growers in high wind areas need more than just sand bags to keep their low tunnel structures secure. Burying the edges is effective, but Johnny’s also recommends putting in stakes on each side of the tunnel, offset, and crisscrossing rope over the length of the structure.
Appropriate crops for winter production in either type of tunnel include: spinach, kale, collards, chard, leeks, scallions, carrots, parsnips, cabbage, parsley and arugula. Many other crops may not survive the entire winter, but their season can begin much earlier and be pushed well beyond the first frost.
What is the potential for low tunnels in Kansas? “There is very little research or awareness out there about the potential of low tunnel production,” explains Dan Phelps, Tunnel to Table Activity Coordinator for KRC. “By increasing the number of growers experimenting with low tunnels in Kansas, we hope to increase our understanding of the unique possibilities these structures can offer in our state.”
Eliot Coleman, who is largely responsible for the advancements seen in low tunnel technology nationally, has spent decades perfecting his techniques, through trial-and-error. Whereas snow is the major challenge on his farm in coastal Maine, Kansas farmers are tasked with experimenting and finding creative ways to overcome the challenge of high winds.
Tobacco Road Farm in central Connecticut is a shining example of the potential of low tunnels. For the past decade, they have opted out of using high tunnels entirely, and strongly favored the benefits of low tunnel production. Low tunnels now cover more than an acre of their farm.
“The seeding dates for their winter and spring low tunnel crops are astonishingly late,” writes Tracy Frish about Tobacco Road Farm’s capacity to harvest low tunnel crops year-round (Growing for Market, July 2006). “They continue planting through the beginning of December and start up again in February… Normally, harvest continues until Christmas and then resumes in March. The mild winter of 2005-06 allowed them to harvest at intervals in January and February as well.”
The estimated annual operating cost for Tobacco Road Farm’s low tunnels is three cents per square foot – due to the fact that they use galvanized metal wire for hoops instead of metal hoops (they say the wire bounces right back from heavy snow loads) and they use two layers of one-and-a-half mil. construction-grade plastic (compared to the typical, heavier weight, more expensive, four to six mil. greenhouse grade plastic).
What are some low tunnel options for Kansans? As this Connecticut farm demonstrates, there are many options for low tunnels configurations – including using shade cloth, different thicknesses of row cover, or different types of plastic than the standard greenhouse plastic found on high tunnels. As is explained below, each configuration offers its own unique benefits.
Shade cloth can be used without plastic on low tunnels, to extend the season of cool season crops into the warmer months. This can be especially effective when combined with misters set on timers.
Low tunnels covered with row cover allow air and water to penetrate while providing several degrees of frost protection. Though row cover does not offer the daytime temperature increase that plastic covered low tunnels can provide, on sunny days it can be beneficial that no ventilation is required.
Using thick row cover on low tunnels can help give warm season crops a jump start in the spring and can help extend the growing season past the first frost, perhaps as late as winter solstice (but not for overwintering crops). Thick row cover also protects crops from the wind, though additional measures must be taken in high wind areas to keep the row cover attached.
Thinner row covers offer little cold protection, but instead serve as physical barriers to insects – preventing pests like squash bugs and cucumber beetles from reaching the crop. However, many tunnel crops require pollination from beneficial insects. In these cases, the row cover is removed for pollination once the plants start flowering, at which time the plants are established enough to deal with some pest pressure.
Perforated plastic provides about as much frost protection as row cover but also provides much higher daytime temperatures – similar to those of greenhouse plastic. However, unlike greenhouse plastic, perforated plastic self-ventilates when temperatures reach a certain point and the slits in the plastic walls contract, allowing heat to escape.
Kansas high tunnel farms growing in the winter can also benefit from the additional warmth provided by low tunnels placed within the high tunnel. While a high tunnel with a single layer of plastic provides one hardiness zone of protection, adding a plastic covered low tunnel will provide one additional zone of protection. This combined low-and-high-tunnel method allows, for example, crops grown in zone 5 to be grown in a climate controlled environment equivalent to zone 7 – which is like the equivalent of moving your operation from Topeka to Dallas!
The Kansas Rural Center asks growers with any experience using low tunnels or high tunnels, to complete the Kansas High Tunnel Survey located at www.kansasruralcenter.org/T2Tsurvey. Lessons learned from this survey will be integrated into informational Tunnel to Table publications, to be released later this fall.
The most up-to-date information on KRC’s Tunnel to Table program is available at: http://kansasruralcenter. org/category/tunnel-to-table/, or by contacting Program Coordinator Cole Cottin at ccottin@kansasrural center. org or 785- 992-4572.
From September-October 2014 Rural Papers