Organic Under Glass and Plastic

Today is the last day of the blogs on the Organic Track from the Great Plains Growers Conference.

Organic Under Glass and Plastic presented by Chris Blanchard, Rock Spring Farm in Iowa who has a 200 member CSA

High tunnels can be used as an effective means of significantly extending the growing season. This gives growers the advantage of being able to market produce earlier in the spring and later into the fall. A well managed high tunnel can even enable growers to produce certain crops throughout the winter. Mr. Blanchard’s suggestion for an ideal high tunnel set up is a mobile unheated structure, covered in a double layer of plastic. A movable high tunnel allows the grower to utilize the benefits of enclosed growing space for significantly more crops than a stationary tunnel.

An intensive management system is vital. This begins with a well planned production schedule and production map. Fall planted cold-hardy crops must be planted according to a strict schedule, as a lost day in fall is like a lost week in the spring (shortening day lengths diminish growing time). Movable high tunnels should be allotted three patches of growing space so that a succession of crops can be easily mapped and planned. For example, cold-hardy spinach and salad greens can be planted in plot 1 during late winter. Once exterior conditions warm enough for the greens to thrive outdoors, then the high tunnel can be moved to plot 2 and tomatoes can be started in early- to mid-spring. During late-summer, lettuce and carrots can be planted outdoors in plot 3 and the high tunnel can be moved onto this plot in mid- to late-fall. Meanwhile, super cold-hardy leaks can be planted outdoors in plot 1 during late spring and the high tunnel can be moved to cover them in mid-winter. Stationary tunnels should also be intensively planned, but space constraints will limit the grower to fewer crops than with a movable tunnel.

There are challenges to consider when growing in high tunnels: water condensation, salt build-up in soil, soil drying, and pests. High tunnels must have proper ventilation in order to avoid condensation, which can cause bacterial and fungal issues. Soil salinity can also become a problem because most irrigation systems do not adequately drench the soil enough to flush out salts. Similarly, soil drying can happen, especially with drip irrigation. Both of these issues are less of a problem with movable high tunnels, as rain flushes the soil when the plot is uncovered. However, if the high tunnel is stationary, the soil would benefit from occasionally over-irrigating. Ideally, high tunnels serve as a physical barrier against pests. However, if a pest population is able to infiltrate the tunnel than they can become a big problem (the protected growing environment is ideal for both plants and pests). To solve for this, Mr. Blanchard suggests releasing numerous predator insects (ex. parasitic wasps) within in the high tunnel every spring.
(report by Rachel Deffenbaugh – Gateway Greening, Inc., St. Louis, MO)