Excessive solar energy and wind can wreak havoc on greenhouse inventory if not protected sufficiently. When solar energy is converted to heat energy, it strikes plant leaves, resulting in excessive air, leaf, and soil temperatures. Placing plants under a 30 to 50 percent shade in the middle of the summer can lower leaf temperature by 10°F or more. This along with reduced wind speeds can significantly lower transpiration water losses during the growing season.
Shade structures or shadehouses, are important tools for modifying indoor growing environments in order to effectively extend the growing season in cold and warm weather alike.
Shadehouses have multiple applications in a variety of plant production operations. For example, when it comes to greenhouses, they are useful for hardening off plants, reducing light levels, and lowering growing temperatures. For nurseries they provide warm and cold weather protection while keeping animals away and reducing irrigation needs. When it comes to garden centers, they are useful in reducing temperatures for customer comfort and plant health.
There are four types of shadehouses with which growers should be familiar.
Lath houses. The original shadehouses were called lath houses. They were frame structures covered with wood lath, hence the name. Most were made with poles set into the ground with 2-inch framing lumber nailed to the poles to support the lath. A 50-percent shade was created by leaving a space equal to the width of a lath between adjacent laths. Today, most shade structures are covered with either polypropylene, polyethylene, polyester, or a composite fabric, which usually contains aluminized polyester strips.
Cable frame shadehouses. The cable frame shadehouse probably evolved from the shade tobacco industry where several thousand acres are covered annually in Connecticut and other states to modify the environment to produce tender tobacco leaves for the wrappers of the best quality cigars.
Construction consists of posts surrounded by concrete, which are set into the ground on an approximate 20-foot x 20-foot spacing. The height can be 8-feet to 16-feet. Deadmen located around the perimeter provide the bracing for the tension in the wires. Stainless steel cables with adjustable turnbuckles are strung between the posts to support the cloth shade material that is attached with clips or hooks. Shade material hung on the sidewall around the perimeter is attached to the upper wire and usually buried in the soil. This provides wind protection to the plants.
Rigid frame shadehouses. In rigid frame shadehouses, the cable is replaced by pipe or rollformed truss members. This supports the shade cloth. Instead of deadmen, horizontal and vertical diagonal knee braces create the rigid frame. Post spacing is less than with the cable system, usually 10 feet to 18 feet. Shade material can be attached with tek screws or clips.
Retractable roof shadehouses. As solar radiation varies considerably over the day and from season to season, the main advantage of the retractable design is the ability to regulate the amount of sunlight that reaches the plants. Increased growth of the plants results as ventilation can be controlled to reduce temperature. Ventilation can also reduce the incidence of disease. Reducing sunlight intensity can lower irrigation needs as both the plants and the soil are kept cooler.
Both cable and truss style retractable roof designs utilize standard energy/shade screen technology for opening and closing. One gear motor can handle up to 50,000 square feet of growing area. The shade material is usually stored at the post line and may be protected from sun and snow by a hood.
Most retractable shadehouses are available with roll up sidewalls. These use a conventional roll up mechanism and small gearmotors. This provides ventilation on demand and also accessibility for plant handling.
In areas where protection of the plants from snowfall is important, an A-roof design is available. The A-roof can be covered with an impervious material that sheds the snow and rain to a gutter for removal. Supplemental heat can also be added if desired.
Today’s shadehouses, with their improved technology and design, are not only providing growers with low-cost options for protecting valuable inventory, they’re also proving themselves to be space savers. That is, by sustaining and improving production, shadehouses are lessening the need for some growers to add more greenhouse space.
Low cost, less space, and overall improved production make these structures important tools for growers everywhere.
John Bartok is a regular contributor to Greenhouse Management and an agricultural engineer and emeritus extension professor at the University of Connecticut. He is an author, consultant and a certified technical service provider doing greenhouse energy audits for USDA grant programs in New England.
Have a question? You can write John at firstname.lastname@example.org.