by Kim Dieter

Created on: April 10, 2010

During the long, hot days of summer, greenhouses can become extremely warm and plants do not grow well in hot temperatures.  There are several factors to consider when preparing a greenhouse for summer.  Should the greenhouse be full of plants during the summer?  Or, should the greenhouse be closed and not used? 

 Most plants grow best at temperatures lower than 90 to 95 degrees F.  Because greenhouses are enclosed structures covered in glass, fiberglass or plastic, they can become much warmer than 90 degrees during the summer.  If the greenhouse will be used during the summer, plans must be made to keep the interior temperature at the optimal growing temperature for the plants.

 There are several methods of cooling the interior of the greenhouse 10 to 20 degrees lower than the outside temperature.  Vents or louvers that can be manually or automatically opened will allow outside air to enter the greenhouse.  Exhaust fans can be installed on one end of the greenhouse and intake shutters installed on the opposite end.  The fans blow hot air out of the greenhouse and bring cooler air inside. A misting system installed along the top of the greenhouse can be used in conjunction with the fans.  If the greenhouse is a hoop-style, usually PVC pipe covered in polyethylene, the sides can be rolled up on warm days. The use of shade cloth will also reduce the interior temperature.

 In areas with lower humidity, an evaporative cooler (also known as a swamp cooler) can be installed.  Or, wet pads can be installed on one end wall and fans installed on the opposite end.  In either case, the pads or cooler is attached to a hose for a constant water supply.  The size of the cooler or pads depends on the square footage of the greenhouse. 

 It is very helpful to install a thermometer that records minimum and maximum temperatures inside the greenhouse.  It is also recommended to have an automatic ventilation or cooling system operated by thermostats rather than relying on a system that must be manually operated.  In the summer, one hot day without ventilation or cooling could damage many plants.

 The second alternative is to close the greenhouse for the summer.  Plants can be moved outside or to shade houses.  A closed greenhouse will become very warm and will create an inhospitable environment for insects, some disease causing organisms and weeds.  The greenhouse can be put back into use when the days are cooler in the fall.

 With careful planning, a greenhouse can be successfully prepared for summer.

 Reference:

 http://www.umass.edu/umext/floriculture/fact_sheets/ greenhouse_management/jb_ventilation.htm

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