Promoting sustainable development and the
wise use of natural resources
Promoting sustainable development and the
wise use of natural resources
2. High Tunnel Farming (North Carolina). Sanjun Gu. 2021. 68pp.
The advantages and disadvantages of high tunnels are presented in the beginning of the paper. This is one of the only high tunnel papers that states the disadvantages of using high tunnels which include: more expensive than field production, labor intensive, irrigation required, not resilient to extreme weather (common in Alaska), can concentrate pests, and fertilizer salt buildup (Gu 2021). The paper states many advantages of using high tunnels as well; the most salient of these is that in North Carolina a high tunnel can offer up to 4-6 weeks of season extension. Multiple technical topics are covered including considerations for building high tunnels, what to grow as well as soil health and environmental management.
There are many things to consider when placing the high tunnel within the landscape and selecting the appropriate structure. At the time of the paper and in North Carolina, NRCS would finance up to 1/20th of an acre (30’x72’) but this is a larger size high tunnel than many smaller growers might not be able to manage. The building site should be elevated with prospective French drains preliminarily located to aid in drainage and the high tunnel oriented north south above 40 degrees latitude except when parallel to the prevailing winds. Producers should be wary of ridge ventilation in snowy and windy areas and extra structural supports are always recommended. There can be significant costs to construction after materials are paid for (up to 60%). Scaffolding, hydraulic lifts, and other heavy equipment with buckets may be needed to install the bows (hoops/ribs) and would need to be used on unprepared or frozen soil. If designing a high tunnel from scratch, PVC should not be used for bow or structural supports because it can deteriorate plastic where it comes into contact. Use of PVC can actually void a warranty if there are problems associated with its use. Johnny’s offers a Quickhoops HT using electrical conduit available from local hardware stores. High tunnels are particularly susceptible to extreme weather conditions, which are common in Alaska. Winds greater than 25 mph can rip high tunnels apart. Heavy snow may necessitate cutting plastic covers to save the structure. Consider purchasing sturdier high tunnels for zones below a 7.
The initial planning phase for what to grow in high tunnels should address effective use of vertical and horizontal space, best value for effort, pollination, matching the season type of a vegetable to management of the high tunnel. When in doubt, new high tunnel users should grow tomatoes. Pollination can be a problem in high tunnels so producers should choose greenhouse varieties (parthenocarpic). Vertical space should be utilized by trellising and growing more compact varieties. Farmers can use intercropping to maximize space and should always make sure that crop selection considers local markets and their operation. The best values are typically from fruits and fruiting vegetables like berries, tomatoes, cucumbers, and peppers. Tomatoes are an excellent starting point for new high tunnel users because they are high value, relatively easy to grow, and benefit greatly from the high tunnel environment. There are good definitions of season types of the vegetables including hot season, warm season, cool season, and cold season as well as their preferred temperature ranges and ideal soil temperatures.
Managing soil health in the high tunnel environment is more different than field operations because there is no rainfall, not a lot of space to implement complimentary conservation practices, and there can be buildup of salinity and alkaline soils over time. The author suggests growing cover crops as part of the crop rotation and on the season ends if there is sufficient growing season. Cover crops need to be terminated using a flail mower at least two weeks prior to planting cash crops. Compost should be added every year in a one-inch layer and incorporated into the soil. About 40% of the chemical fertilizers should be added at pre-planting to the top 6-12” of soil. Add remaining 60% throughout the season through side dressing or fertigation. Layout beds along long-end of high tunnel and use plasticulture to help with warming the soil and managing weeds. Plants should receive about 1 inch of water per week depending up on the soil type. Sandier soils may need to be water more and less frequently while clay soils may need smaller amounts more frequently. The temperature management of the high tunnel including ventilation is different for different season vegetables and this should be considered when selecting what to grow because different parts of the high tunnel are not management differently.
