Plastics in the Garden
GLASS VERSUS PLASTICS
Despite some small loss due to reflection and absorption, glass transmits all the light that plants need. It is easily cleaned, is durable, and any water on it escapes quickly. On the other hand, it is fragile and needs a rigid structure to support it.
Glass is extremely efficient in conserving heat, whereas polythene, being less transparent, is highly susceptible to all forms of radiation, both hot and cold. The temperature under polythene can actually be lower than in the open, and is usually 10° F. (5° C.) or lower than that in a glass greenhouse. However, the thicker transparent plastics, such as PVC, rival glass in their efficiency, and are extremely versatile.
GREENHOUSES, FRAMES AND CLOCHES
Inexpensive, frames and cloches can be constructed of plastic or polythene, which for outside covering should have a gauge of at least 500. The material is light, and only a simple and reasonably light wooden framework is needed. The plastic is held between strips of wood, which can be screwed down after the plastic has been stretched taut, making it possible to construct greenhouses and frames of various sizes.
Although plastic loses heat quickly at night, it does enable the gardener to raise-plants in early spring, and to produce early crops of such summer vegetables asand . Condensation may however be extremely heavy unless the house or frame has plenty of ventilation and a reasonable amount of heat. Since plastic and polythene do not last much more than 18 months or two years, depending on weather conditions and the position of the structure, it is usually uneconomical to use these materials for large greenhouses.
Plastic is particularly valuable in the construction of cloches, when it can be mounted on a simple wire or wooden framework. These structures are very light, and should be well anchored into the ground to prevent them from being blown away or disturbed.
Polythene sheeting is extremely useful for protecting plants from rain, and it also makes an excellent lining for a glass greenhouse, as a means of conserving hear. In this case, thin material of 50 or 150 gauge should be used.
Sheets of green polythene can be used to shade the greenhouse, and can either be attached inside the house or purchased as ready-made roller blinds.