Choosing a Greenhouse Covering by Yasu Yamada
The greenhouse covering you choose will determine the amount and type of light reaching your plants, your plants’ rate of growth, the greenhouse’s ease of maintenance and related labor costs, it’s durability, safety and overall appearance.
Glass/Rigid Plastics
The most traditional covering for a greenhouse, glass, is durable and transparent and is often chosen for it’s permanence and it’s classic beauty. However, there are some disadvantages to using glass. It is much heavier and more breakable than other greenhouse coverings and requires a heavy seal around the structure’s joints to keep heat from escaping. The price of glass can run from $0.85 to over $7.00 per square foot, depending on characteristics like thickness and added features. Tempered glass is stronger and will be more expensive than non-tempered glass.
An alternative to glass is a rigid plastic. This category includes fiberglass, acrylic, and polycarbonate panels, which are available in corrugated and flat forms. Shatterproof, they resist damage and are known to retain heat well. When purchasing polycarbonate panels, make sure they are UV coated to guard against premature yellowing. Fiberglass usually costs between 75 cents to a $1.00 a square foot and polycarbonate panels cost between $1.00 and $1.20, depending on thickness and added features such as anti-condensation or UV ray coating.
Films
There are a variety of plastic films on the market including polycarbonate and polyethylene films. These films offer a lightweight and more affordable alternative to glass. Unfortunately, most films start to degrade after about 2-4 years and need to be replaced regularly. Under strong environmental conditions, like the sunlight of California’s central valley, films can degrade even faster. The thickness of films can range from 1 to 15 mil, and the cost can vary from about $0.05 to $0.16 per square foot for a single layer, depending on the width of the film and the treatments that may be included.
Greenhouse covering manufacturers continue to improve on the existing technologies. One example of a new covering product is an ethylene-tetrafluoroethylene copolymer (ETFE) film that was developed by Asahi Glass Company of Japan. While most plastic films offer 85-86% light transmittance, F-CLEAN’s chemical composition allows for about 95%. This can lead to a variety of results, including a shortened growth cycle, brighter colors in the crops, and more production.
California Florida Plant Company, L.P. installed F-CLEAN in October 2001 to grow carnations. “I usually use polycarbonate, but I sectioned off a trial space of about 4 acres with F-CLEAN. The carnations are producing a broader leaf and the plants are greener in color,” stated General Manager Oscar Hasegawa. “And, the flowers will be ready for harvest about one week earlier than usual.”
Higher light transmittance can make a significant difference for plants that require a lot of light, especially in the early morning and in the winter months when the sun is not as strong. Japanese begonia, hydrangea, and poinsettia growers have all reported brighter colors, while eggplant, spinach, onion and tomato growers have all reported that the extra light transmittance has improved their crops in terms of color, speed of growth, strength and overall health.
F-CLEAN also contains a self-cleaning substance that makes covered greenhouses easily cleaned by rain or snow. In addition, F-CLEAN’s tensile and tear strengths are higher than other plastic films and its useful lifetime usually exceeds fifteen years, which reduces replacement and labor costs. F-CLEAN costs about $1.00 per square foot for a single layer.
When choosing a greenhouse covering, take into consideration the type of plants you will be growing, the amount of sunlight you want, and your budget for material and future maintenance. Whatever you choose, a greenhouse covering is an investment that should be customized to your needs and environment.
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