MariMed employs 24/7 monitoring and control to adjust temperature, humidity and lighting. The high-resolution cameras also allow for remote visibility of the plants' overall health.
Photo courtesy of John W. Bartok, Jr.

Shading, along with ventilation, reduces the temperature and light levels in a greenhouse. By blocking or reflecting the sun’s radiation, a significant portion of the heat load can be excluded.

This can save energy by reducing fan operation and extending the time that carbon dioxide (CO2) enhancement can be used.

Shading also reduces excessive light levels that may burn or dry plant foliage. For most plants, a photosynthesis saturation level of 4,000 to 5,000 foot-candles (800 to 1,000 µmol/square meter per second) is adequate. Shading also diffuses light in the greenhouse for more uniform and deeper penetration into the lower foliage.

Follow these pointers that shed light on shading techniques:

1. Choose exterior shade for free-standing or hoop houses.

Low-cost shade compounds can be sprayed or rolled on the glazing at different levels to achieve constant light reduction. Select a material specific to your glazing that can be easily removed in late fall to allow for full winter sunlight.

Shade fabrics applied over the greenhouse roof are lightweight, easily applied and available in several materials, shade levels and colors. Most materials are ultraviolet (UV) stabilized, and will last about 10 years and cost roughly $0.25 to $0.50/square foot, depending on the type of material and the shade percentage.

2. Choose an interior movable shade screen for gutter-connected houses.

Interior screens provide shading and heat-energy conservation. When retracted on cloudy days, they provide maximum available light for photosynthesis. When closed at night during the heating season, they save up to 35 percent of heating costs. Shade screens also reduce condensation on leaf surfaces. Select an open mesh for greenhouses with roof vents or closed mesh for exhaust fan-cooled houses. Translucent materials provide some shade and can be left closed during the day for additional energy savings.

3. Factor in cooling capabilities.

Research at North Carolina State University and Rutgers University has shown that additional cooling can be achieved by misting to keep the shade material wet. This is achieved by evaporative cooling. Air movement from wind and horizontal air flow (HAF) fans can also impact the cooling effect. In the future, photoselective materials may offer less heat gain, better plant growth and fewer pest problems.

Editor’s note: For more on light deprivation, see this month’s Hort How-To column, “Deprive to Thrive” on page 98.

John W. Bartok, Jr. is an agricultural engineer, an emeritus extension professor at the University of Connecticut and a regular contributor to Greenhouse Management. He is an author, consultant and certified technical service provider doing greenhouse energy audits for USDA grant programs in New England.