Greenhouse Technology

Introduction

Producing high quality fruit or flowers consistently is one key to a successful business. Greenhouses provide unique opportunities to achieve this goal. Today, there is a vast range of sophisticated technology that can help. This leaflet shows how it is possible to progress step-by-step from simple technology to the most sophisticated. However, to get the full benefit from the available technology you must start with a well designed greenhouse.

Technical possibilities

Technology enables growers to monitor the greenhouse environment, control the physical environment, water and feed the plants, modify the atmosphere i.e. CO2 (carbon dioxide) concentration and relative humidity, and restrict the movement of pests and pathogens. You can also use fumigant pesticides in greenhouses but this leaflet is not about pesticide application technology, although several of the technologies available for greenhouses can help to control diseases and pests and reduce the need to use pesticides (see last page).

Each of the capabilities listed can use technology ranging from simple to sophisticated computer-operated systems. For example, a grower can monitor greenhouse temperatures using a maximum and minimum thermometer and a record book. The greenhouse can be cooled and CO2 levels raised by manually opening vents. However, the highest quality produce is obtained by growing plants all the time in ideal conditions. This is difficult to achieve if growers have to keep checking the thermometer to decide if the vents need to be opened or closed, or if they have to check soil moisture to see if the plants need to be watered. A computer-operated system is obviously much better.

Technical options for greenhouses
Capability	Equipment
Monitor environment	Sensors and recorder
Control environment heating cooling humidity and wetness light	Sensors, automation and controller heater venting, fogging, shading air movement, heater, venting, fogging, suitable building, dehumidifying shading
Irrigate and feed plants	Delivery system, automation, sensors, controller
Adjust carbon dioxide in atmosphere	Delivery system, sensors, controller
Restrict movement of pests and pathogens	Screening and partitions

Step-by-step approach

It is not essential to invest in computer-operated systems immediately. You can acquire equipment as finances allow. However, for growers who want to use more technology to help grow better crops there is not a straight line path from the simple to the ultimate in modern technology. It is possible to automate the watering of plants without automating venting or heating systems. However, there are some steps that should precede others.

A grower should improve the technology in the greenhouse in a planned sequence. Each advance builds on the previous step. For example, to improve temperature control, opening and closing the opening of ridge vents can be automated. The simplest controller is a thermostat. A time clock can be added to ensure the greenhouse is closed at dusk. Eventually, a computer system can be attached to allow more sophisticated decision making. However, there is no point in buying the computer if the operating mechanisms do not exist. Also there is no point in providing extra CO2 if there are inadequate environmental and plant irrigation controls. Plants will only increase yield and quality under extra CO2 conditions if growing conditions are optimised.

Seting the Greenhouse
Feature	Notes
Plan for expansion	Choose a site that will allow more greenhouses to be built and maintain easy access between them and other buildings, both for people and machinery
Shelter from strong winds but no shadows	Shadows from shelter trees or high buildings can cool part of the greenhouse, causing high humidity and condensation that increases the risk from disease.
Weed-free area surrounding greenhouse	Surround greenhouse with at least 10 metres of weed-free grass closely mown or grazed or inert material such as asphalt or concrete. Weeds host many plant pathogens and insects including those that can transmit plant viruses.

Internal arrangements to be considered

Arrangement of plants and passageways

The layout of plants and passageways should allow easy movement of people and equipment. Staff will do a better job if they can move about freely and concentrate on the primary activity. This is particularly true for spraying.

Width of plant beds and benches

Wide plant beds or benches should be avoided. It makes it difficult to tend and monitor plants. Also good coverage by pesticides is more difficult. Air movement can also be poor.

Plant density

More plants does not always mean higher production. Choose a plant density that will allow optimum quality and production. High plant density can make it difficult to get good spray coverage and reduces air circulation increasing the risk from disease. Widely spaced plants are less disturbed and damaged by cultural operations and this helps reduce both the distribution of fungal spores and sites for infection.

Air circulation

Plan the internal layout for efficient air circulation to al parts of the greenhouse. Ensure there is air movement between all plants and that there are no dead spots. Air movement helps keep the plants dry and reduces the risk of diseases.

Watering

Avoid a watering system that sprays the aerial parts of plants. This increases the risk of infection of many plant pathogens. If plants are wetted, make sure that there is a way to dry them by nightfall.

Greenhouse technology to assist disease and pest control
Strategy	Method
Reducing risk of pathogen infection Prevent plants becoming wet at night Prevent long periods of high humidity	Circulate air (preferably warm) through the plants Heating air lowers humidity Venting removes warm wet air Use trickle irrigation or hydroponics Cover greenhouse floor with plastic
Weed control	Cover greenhouse floor with plastic
Reduce risk from root disease	Grow in bags
Restrict pests (birds and insects) entering the greenhouse	Cover vents and other openings with netting
Reduce vigor of pest or pathogen	Keep greenhouse temperature hotter or cooler than the optimum for the pest or pathogen
Increase vigor of biological control agent	Create optimum temperature and humidity for biological control agent
Restrict spread of pests or pathogens	Grow only one crop per greenhouse, disinfest between crops

Conclusion

We all know that greenhouse vegetable and fruit growers have to increase production and the quality of production to remain economically viable. Flower growers also have to ensure that their produce meets the quality requirements of the markets.

To produce the highest quality in adequate quantity, a grower must take full advantage of all the technology available. However, if one key element fails the grower will not be able to achieve the best results. A key element is the structure of the greenhouse and it is essential to start off with a well-designed greenhouse.