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- Greenhouses need to control light with shade cloths.new plants in greenhouse image by ann triling from Fotolia.com
For a commercial greenhouse, plants growing successfully is everything. If plants die because of too much sun, profits are lost. For a feedlot or milking operation, stressed animals are never good. Shade cloth is used extensively by agri-business, but using any cloth will not do. Shade cloth must have temperature and light transmission qualities that are strictly controlled. This being the case, researchers study shade cloth properties extensively and report their findings to the general public - Researchers at the North Carolina State University placed thermocouples on shade cloths and on the ground. A thermocouple is the sensing end of a thermometer. After doing extensive testing, they found a connection between ground temperature and shade cloth temperature. This confirms that shade cloths do reduce the temperature on the area below it. Researchers wetted down the shade cloth, too, but found that wetting has no effect on ground surface temperature.
- In 1961, researchers at the University of California did extensive testing of materials for shade cloth use. Similar to the research at North Carolina State, they used thermometers placed above and below the shade cloth. After data collection, they developed an E-Value scale. The highest number is the most effective material in temperature reduction, with the lowest number the least effective. Six-inch thick hay had the highest value of 1.203, Snow fencing had the least, which was 0.589. Eight-mil-thick black polyethylene had a value of 1.036. Translucent 4-mil polyethylene had a value of .677. This research was a landmark one, since it developed an unbiased, accurate charting of different materials. Greenhouse growers and livestock farmers now could pick what materials to use for what temperature reduction they wanted.
- Researchers at the University of Hawaii ran tests of different-colored shade cloths. They tested semitransparent shade cloths of various colors, including red and black. These cloths allow only a certain color through, while reflecting the rest. Black cloth is opaque and reflects all colors. The tests were done on two species of plants--Janet Craig and Colorama--over a four-month time period. They discovered that red produced the most number of new leaves and shoots in Colorama, with black producing the least. However, the total amount of chlorophyll for Janet Craig was the highest for black. A grower can use these findings to his advantage. Since red produces new growth quicker than black, a greenhouse could use red shade cloth for quicker new growth over just using regular sunlight. As the plants get older, the greenhouse transitions to black shade cloth for higher chlorophyll, or "green" content of the plants. Specific plants may have different growing times for different colors, so botanists would have to further investigate this phenomenon of color effects on growth on different species.
Temperature Correlation Confirmed
Materials Evaluation Testing
Reflected and Transmitted Color Tests
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