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Functions of a Greenhouse
Competencies 7.00-9.00
Functions of a Greenhouse The basic function of a greenhouse is to
provide a protective environment for crop production.
Several factors must be monitored: Temperature Moisture Pest control Nutrition Light
Temperature
Temperature Temperature ranges must be conducive to
crop production The cost of heat is the second highest
expense of greenhouse plant production. (labor is the greatest expense)
Greenhouses lose heat through the plastic, glass, etc. and additional heat has to be provided especially in winter.
Greenhouse Effect The greenhouse effect
is the way greenhouses collect and store heat from the sun.
Radiant energy warms the greenhouse and its contents
Controlling Temperatures There are two ways to
control temperatures in a greenhouse: Thermostats Air or ventilation
Thermostats Thermostats should be at plant level for
most accurate control. There are two kinds of thermostats:
Aspirated thermostat-small fan blows air continuously over the temperature sensing unit to help maintain a more uniform temperature
Thermistor-uses solid state electronics that enable growers to use computers to monitor the greenhouse environment
Temperature Control Equipment Heaters Fans Cooling pads Mechanical air
conditioners Ventilators Shade cloths and
materials Fogging and misting
Moisture
Moisture Moisture must also be
conducive to plant production
Moisture is monitored by Watering Humidity levels
Controlling Moisture Levels Humidistat is used to control fogging or
misting systems to regulate relative humidity (moisture) in the air.
Heat dries moisture from the air and moisture must be added by both watering and through misting and fogging for most plants.
Moisture Control Equipment Watering system Shade cloth Foggers Mist system Humidifiers
Pest Control
Pest Control Greenhouses must be kept free of:
Insects Diseases Weeds Rodents
Pest Control Use proper sanitation practices Control weeds around greenhouse Prevent weeds, insects, rodents, and
diseases inside the greenhouse
Nutrition
Nutrition Nutrition must be monitored in:
Soil Water Air (ventilation is necessary to supply carbon
dioxide)
Light
Controlling Light Levels Photocell measures
light intensity and relays signal to computer that turns on lights or activates the shade cloth to control light
Timer is used to turn lights on or off at a certain time
Light Control Equipment Lights Shade cloths Shade materials Black cloth
Greenhouse Maintenance
Maintaining Temperature Equipment Inspect heaters Use adequate clean fuel Ensure that thermostats are working
properly Inspect fans, fan motors, belts, etc. Check water levels in cooling pads and are
clean Shade cloths should be attached and
applied or removed depending on need
Maintaining Light Equipment Determine need for shade cloths to be
attached or removed Replace light bulbs as needed Ensure that timers and photocells are
working correctly
Maintaining Moisture Equipment Inspect humidistats and fogging or mist
systems Ensure that water lines and faucets are
not leaking Determine if there is an adequate source
of high quality and clean water
General Maintenance Practices Inspect and make structural repairs
Loose, torn or cut plastic covers Broken glass or fiberglass Door locks and fasteners Air leaks Damaged framework and foundation
General Maintenance Practices Inspect and make repairs for controls and
equipment Heaters Fans Pumps Thermostats Humidistats Photocells Timers sprayers
General Maintenance Practices Inspect and make repairs for utilities
Water Electricity Gas or fuel oil Waste and trash disposal