Plastic Greenhouses, its advantages and disadvantages

Plastic Greenhouses

Plastic, as a substitute for glass in greenhouse glazing, is here to stay, but it is still in the experimental stage. It probably always will be, as long as new materials and different uses continue to appear, so you will have to keep yourself abreast of new developments. Two types of plastic generally are used: smooth transparent sheets of polyethylene and vinyl film, and corrugated and special types of plastic such as Fiberglas, Al-synite, Mylar, Filon, and Corrolux. Commercial builders are finding the smooth film plastic increasingly useful, especially when they want economical, rapid construction for additional plantings or a quick seasonal crop and aren’t too concerned with the lasting qualities of the glazing. (See Photo 12.) The more expensive corrugated types have great endurance. Tests indicate they may last 25 years without deteriorating.

If at first you can’t afford to build a regulation glass greenhouse, try one of the transparent plastic types. The investment is low, and growing plants in any kind of a greenhouse is a good way to gain experience.

Those who have had experience with plastic glazing are generally agreed on the following resume: “Plastic glass has exceptionally high strength, with low weight, is shatterproof, translucent to light, resists weathering, is not attacked by rodents or termites, will not rot, and transmits approximately only 40 per cent as much heat as glass.” The last point means that plastic greenhouses are usually cooler in summer and warmer in winter.

Advantages and Disadvantages

Polyethylene, Vinyl, Renolon, or other types of transparent plastic cost about 4 to 16 cents per square foot, depending on thickness. Such plastic is easily attached to the greenhouse framework and all puttying is avoided. It’s possible to construct a small 6- by 8-foot free-standing greenhouse for $60.00 or less-providing, of course, that you do all the work. The modern, improved plastics successfully resist strong winds and heavy snow, and transmit up to 98 per cent of the sun’s visible light energy-as much as passes through good glass. Some plastics also transmit up to 80 per cent of the ultraviolet rays, which is greater than through glass.

Two layers of plastic-one inside, one outside of the glazing frame-with an inch of space between them, provide excellent insulation, thus decreasing the cost of heating. Transparent plastic usually deteriorates rapidly and must be replaced every year or two. Certain new plastics being marketed are said to last up to 5 years.

The corrugated types are expensive. However, these have a long life, never need shading, and are not damaged by hail, snow, or such pests as termites. They admit up to 85 per cent of the sun’s visible rays. They are not ideal for the real sun-loving crops-annuals, geraniums, cacti, etc.-but fine for orchids, African violets, anthuriums, rex begonias, ferns, and similar plants requiring medium- to low-light intensities.
Ventilation for plastic greenhouses is somewhat of a problem. Most of them are ventilated through hinged sash on the walls rather than the roof, but a better system is to have sliding panels in the gable ends to allow more thorough ventilation. Corrugated plastic, slightly rust-tinted in appearance when new, darkens as it ages, gradually shutting out some of the light.

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