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ENERGY CONSERVATION AND PLANT GROWTH BY USING DOUBLE PLASTIC ON GLASS GREENHOUSES1
The percentage difference was 7% and 11% of the tomato crop.
Height and quality of pot chrysanthemums, poinsettias and lilys were different between trial compartments when growth regulators were not in use.
When a recommended program of growth regulators for height control was used, there was no difference in quality and minimal difference in time of flowering.
For many years glass has been the primary covering material for permanent greenhouses in the United States.
There have been many variations and improvements in framing, but most of the old greenhouses are pipe framed with numerous posts.
Such framing makes it very difficult to use internal systems for conserving nighttime heat.
Yet these greenhouses continue to be used since most greenhouse cultural operations are not severely restricted by structural framing.
Posts are often used to secure benches and cross framing can support trellis crops.
A popular approach to achieving nighttime insulation is the use of internal curtains.
White (1977) has shown that annual fuel savings of 33% may be realized with a curtain system in central Pennsylvania.
However, these results assume that the curtains will be well sealed around all posts and structural components to prevent convective heat loss.
Such sealing is very difficult in old pipe framed greenhouses.
In cold climates, drawn curtains insulate the heat from the glass roof and can result in glass breakage or greenhouse collapse due to snow loading and ice formation.
Curtains also allow the glass to become thickly frosted on very cold nights, resulting in reduced light for longer periods on cold winter days.
Space necessary for curtain movement can reduce crop growing area and crop yield by shading during storage.