greenhouse functions and controls

8/3/2019 Greenhouse Functions and Controls

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Greenhouse Functions andControls

Horticulture II


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Greenhouse Basics

Plants grow naturally outside, so why dowe need a structure to grow them in?

What is the purpose/function of agreenhouse?

The basic function is to provide a

protective environment for crop(plant)production.


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Greenhouse Environment

What things make up the greenhouseenvironment?

Temperature

Moisture

Pest Control

Nutrition


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Temperature

Different plants have different temperaturepreferences 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 rangethat is conducive to plant growth.

Grow plants together that prefer the sametemperature range.


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Moisture

Just as temperature matters, so doesmoisture.

Some plants need dry environments, whileothers need very wet environments.

How are moisture levels controlled?

Watering

Humidity

Level of water vapor in the air.


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Pest Control

One of the biggest problems growersface is pest control.

What types of pests?

Insects (aphids, whiteflies, etc)

Diseases (fungus, bacteria, viral)

Weeds (oxalis, henbit, etc)

Rodents (mice, rats)


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Nutrition

Plants, like animals, need nutrients to survive.

Growers provide plants with the nutrients they

need by supplementing either the water orsoil with added nutrients.

Growers also have to ensure adequateventilation.

Carbon dioxide


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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 highestexpense.


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What is the greenhouse effect?

Lets try a demonstration to find out.

You will need:

Scissors

Plastic wrap or bag

Popsicle sticks

Glue

Tape


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Building your Greenhouse

Attach your Popsicle sticks together tobuild a small house or box.

Cover the entire structure with plastic,leaving the bottom uncovered.

Tape the plastic to the greenhouse


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The Greenhouse Effect

Place your completed greenhouse onthe window sill.

Note the temperature on thethermometer by the window.

At the end of the period we will put the

thermometer in your greenhouses tosee what happens.


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Environmental Control

In order for a greenhouse to beeffective, the greenhouse environment

has to be closely controlled. What happens if the environment is not

controlled?

How do we ensure that the environmentis kept constant?


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Environmental Controls

In a greenhouse we use environmentalcontrols to manipulate and control the

environment. Thermostats

Temperature

Humidistats

Humidity

Photocells Light


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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 ofit).


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Heat Loss

Greenhouses, while efficient collectorsof heat, are not good at storing it.

Heat is lost through the greenhousecovering (called glazing) and additionalheat may have to be provided.

Especially in winter.


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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, operateexhaust fans or intake fans which pullair through a pad cooling system.


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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


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Aspirated Thermostats

An aspirated thermostat utilizes a smallfan which blows air continuously over

the temperature sensing unit. This helps to maintain a more uniform

temperature.


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Thermistors

A thermistor is a relatively new control thatutilizes solid-state electronics.

These devices allow the grower to usecomputers to monitor and control thegreenhouse environment.

Growers can set defined temperature ranges

for certain time periods and the computersturn heat and cooling devices on and off asneeded to maintain the desired temperatures.


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Light Control

Light levels have to be monitored ingreenhouses to ensure that plants are

receiving the correct amount. Photocells measure light intensities and may

relay that information to computers that turnson additional lights or activates a shade cloth

to reduce light. Timers may also be used to lights on or off at

certain times.


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Moisture Control

Moisture in the air (humidity) should also beclosely monitored for optimum growingconditions.

A Humidistat measures the relative humidityin the air and controls fogging or mistingsystems to regulate the humidity.

Humidity changes as heat dries the moisturefrom the air.

Moisture must be added by both watering andfogging or misting for most plants.


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Summary

The greenhouse environment has to beclosely monitored so that plants grow in

the best possible conditions. A plantthat grows in an environment wheretemperature, moisture, light, nutrition,

and pest levels are ideal and continuouswill be as strong and healthy as it canpossibly be.

greenhouse functions and controls

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