greenhouse functions and controls horticulture ii
TRANSCRIPT
Greenhouse Basics
Plants grow naturally outside, so why do we need a structure to grow them in?
What is the purpose/function of a greenhouse?– The basic function is to provide a
protective environment for crop(plant) production.
Greenhouse Environment
What things make up the greenhouse environment?– Temperature– Moisture– Pest Control– Nutrition
Temperature
Different plants have different temperature “preferences” for optimum growth.– Some plants prefer cool or even cold temps– Some plants prefer warm or hot temps
The trick is to provide a temperature range that is conducive to plant growth.– Grow plants together that prefer the same
temperature range.
Moisture
Just as temperature matters, so does moisture.
Some plants need dry environments, while others need very wet environments.
How are moisture levels controlled?– Watering– Humidity
• Level of water vapor in the air.
Pest Control
One of the biggest problems growers face is pest control.
What types of pests?– Insects (aphids, whiteflies, etc)– Diseases (fungus, bacteria, viral)– Weeds (oxalis, henbit, etc)– Rodents (mice, rats)
Nutrition
Plants, like animals, need nutrients to survive. Growers provide plants with the nutrients they
need by supplementing either the water or soil with added nutrients.
Growers also have to ensure adequate ventilation.– Carbon dioxide
Greenhouse Operating Expenses
In addition to the cost of plants, pots, soil, fertilizer, etc, growers also have to deal with two other MAJOR expenses.– Labor– Heat
Labor is usually the greatest expense. Heat is usually the second highest
expense.
What is the greenhouse effect?
Lets try a demonstration to find out. You will need:
– Scissors– Plastic wrap or bag– Popsicle sticks– Glue– Tape
Building your “Greenhouse”
Attach your Popsicle sticks together to build a small house or box.
Cover the entire structure with plastic, leaving the bottom uncovered.
Tape the plastic to the “greenhouse”
The Greenhouse Effect
Place your completed greenhouse on the window sill.
Note the temperature on the thermometer by the window.
At the end of the period we will put the thermometer in your greenhouses to see what happens.
Environmental Control
In order for a greenhouse to be effective, the greenhouse environment has to be closely controlled.
What happens if the environment is not controlled?
How do we ensure that the environment is kept constant?
Environmental Controls
In a greenhouse we use environmental controls to manipulate and control the environment.– Thermostats
• Temperature
– Humidistats• Humidity
– Photocells• Light
The Greenhouse Effect Summarized The greenhouse effect is the way
greenhouses collect and store heat from the sun.
Radiant energy (the heat you feel when near something hot) warms the greenhouses (and whatever is inside of it).
Heat Loss
Greenhouses, while efficient collectors of heat, are not good at storing it.
Heat is lost through the greenhouse covering (called glazing) and additional heat may have to be provided.– Especially in winter.
Heat Control
Heat, or more specifically temperature, has to be closely monitored and continually adjusted in a greenhouse.
Temperature in a greenhouse is monitored by a thermostat, which controls sensors to open vents, operate exhaust fans or intake fans which pull air through a pad cooling system.
Thermostats
Where should a thermostat be located?– Ideally they should be located at plant level
for the best and most accurate control. Thermostat types
– Aspirated– Thermistor
Aspirated Thermostats
An aspirated thermostat utilizes a small fan which blows air continuously over the temperature sensing unit.
This helps to maintain a more uniform temperature.
Thermistors
A thermistor is a relatively new control that utilizes solid-state electronics.
These devices allow the grower to use computers to monitor and control the greenhouse environment.
Growers can set defined temperature ranges for certain time periods and the computers turn heat and cooling devices on and off as needed to maintain the desired temperatures.
Light Control
Light levels have to be monitored in greenhouses to ensure that plants are receiving the correct amount.
Photocells measure light intensities and may relay that information to computers that turns on additional lights or activates a shade cloth to reduce light.
Timers may also be used to lights on or off at certain times.
Moisture Control
Moisture in the air (humidity) should also be closely monitored for optimum growing conditions.
A Humidistat measures the relative humidity in the air and controls fogging or misting systems to regulate the humidity.
Humidity changes as heat dries the moisture from the air.
Moisture must be added by both watering and fogging or misting for most plants.