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