GREENHOUSE MANAGEMENT

Learn How to Manage a Greenhouse Effectively

Effective greenhouse management requires efficient control of the greenhouse environment. This course teaches you how to select the right greenhouse, site it correctly and efficiently control the greenhouse climate, pests and diseases, lighting, irrigation, and fertilisation. You will also learn about greenhouse automation systems and robotic applications for greenhouse production.

Lesson Structure

There are 9 lessons in this course:

1. Types of Greenhouses
   • Greenhouse Designs for Commercial Nursery Production
   • Greenhouse Construction Methods and Materials
   • What Type of Greenhouse is Appropriate for Your Nursery?
   • Siting Greenhouses
   • Greenhouse Benching
   • What Can You Grow?
   • Environmental Control in Greenhouses
   • Computerised Environmental Control
2. Growing Systems and Equipment
   • How to Grow Plants
   • Measuring Conditions Inside a Greenhouse
   • Environmental Control Systems
   • Getting Plants to Flower Out of Season
3. Pest and Disease Management in Greenhouses
   • How to Stop Pests and Diseases Entering the Greenhouse
   • Detecting and Controlling Pests and Diseases in the Greenhouse
   • Common Greenhouse Diseases
   • Disease Control
4. Temperature Management
   • Temperature Control in a Greenhouse
   • Heating Systems
   • Ventilation Systems
5. Water Management
   • Greenhouse Irrigation
   • Soil and Water
   • When to Irrigate
   • The Nursery Irrigation Program
   • Plants and Water
   • Equipment and Methods
   • Maintenance of Watering Systems
6. Nutrition Management
   • Irrigation and Nutrition Control
   • Liquid Feed Systems
7. Managing Light
   • Importance of Lighting in a Greenhouse
   • Artificial Lighting
   • Measuring Light
   • Controlling Light in the Greenhouse
   • Photoperiod Manipulation
   • Growth Rooms
   • Efficient Lighting Control
8. Managing Gasses
   • Carbon Dioxide Enrichment
   • Pollutant Gases
   • Temperature Control Systems (Ventilation)
9. Automation and Robotic Applications for Greenhouse Production
   • Automation in Vegetable Nurseries

Aims

• Compare different types of greenhouses to better match the plants to be grown inside the greenhouse to be built.
• Explain the equipment and measuring devices (manual and automated) used inside a greenhouse to help grow plants more effectively.
• Explain options for reducing the impact of pests and diseases on plants grown inside greenhouses.
• Detect and control the temperature within an optimal growing range for plants being grown in a greenhouse.
• Control water in a greenhouse, including irrigation and humidity.
• Control nutrient levels in a greenhouse at optimal levels for plant growth and health.
• Explain how light levels can be maintained in a greenhouse for optimal plant production.
• Explain how to best manage the air characteristics inside a greenhouse.
• Explain how greenhouse production can be automated.

WHAT CAN YOU GROW IN A GREENHOUSE?

A greenhouse may be heated or unheated and have a fully manual ventilation system. The unheated greenhouse is the simplest to manage. However, it must be remembered that although a cold greenhouse will trap heat from the sun during the day, thereby extending the growing season, temperatures within the structure overnight can be as cold as the temperature outside. Plants that are frost sensitive cannot be grow in an unheated house over winter. Heating systems will add to the cost of running a greenhouse however simple systems are available for the small grower. Ensuring that the temperature within the house does not fall below 5-7 degrees Celsius will extend the range of crops that can be grown.

Whatever your reason for growing plants in your greenhouse e.g. to propagate new plants, to grow tropical plants in cooler climates, to protect cold or frost sensitive over winter, etc. it is not usually advisable to try to use the greenhouse for more than one purpose.  This may be acceptable for the hobbyist, but not for the commercial grower.  The hobbyist who uses their greenhouse for multiple purposes must resign themselves to the fact that they will not be able to get the best from their greenhouse in all areas of use.

Plant Needs

Every variety of plant has specific needs and tolerances with respect to the environment in which it grows. The horticulturist talks about ‘optimum conditions’, ‘tolerated conditions’ and conditions which are ‘not tolerated’.
Optimum conditions are the conditions in which the plant grows best. Some plants have a wide optimum range, perhaps growing just as well at any temperature from 18 to 28°C. Other plants have a narrow optimum range e.g. growing well at temperatures from 24 to 26°C.

Tolerated conditions are the conditions under which the plant will survive, but not necessarily grow e.g. a plant might have an optimum temperature range of 20 to 26°C, and a tolerant range of  2 to 49°C. The not tolerated range refers to if conditions go outside of the tolerated range. Here, the plant would die or at least be damaged. 
Note: These same principles apply equally to light, moisture, and other environmental conditions for a plant.

Environmental Factors Affecting Plant Growth

The key environmental factors influencing plant growth are:

• Atmospheric temperature - the air.
• Root zone temperature - the temperature of the soil or growing media in which the plant roots are growing.
• Water temperature - temperature of the water used to irrigate the plants.
• Light conditions - shaded, full light, dark.
• Atmospheric gas - chemical components of the surrounding air. Plants give off oxygen but take in carbon dioxide during photosynthesis. Plants will take in some oxygen during respiration (converting stored foods such as glucose into energy) and release some carbon-dioxide, but in an enclosed environment the amount of carbon-dioxide in the atmosphere will soon diminish.
• Air movement – movement of air through the space and around plants. Good air movement mixes gases and evens out temperature fluctuations.
• Atmospheric moisture - the degree of humidity.
• Root zone moisture - water levels in the soil or media.
  
  

Environmental Controls

Growers manipulate the environment to create ideal conditions for the growth of plants. To do this, they use different types of equipment to control such growth factors as temperature, light intensity and duration, humidity and in some instances even the levels of different gases in the air.

Natural Light

Light is the source of energy for plants, and light energy combines with carbon dioxide and water to commence the process of photosynthesis. Therefore, it is important to ensure that maximum light intensity is provided in autumn through winter to achieve plant growth. The design of the structure and its orientation determine the light intensity. 

Other factors include the frame of the structure. If a timber frame is used, it must be painted white to reflect the light. The covering material: glass transmits up to 89% of light; polyethylene 84% and fibreglass starts high but quickly diminishes as the material hazes from the UV rays. Also, as the covering accumulates dust and grime, light intensity can be reduced by up to 20%. Therefore, it is essential the glass is cleaned after the hottest part of summer.

Temperature of Air

Greenhouses require cooling during the summer months. Most locations experience temperatures that are detrimental to plants during summer. Temperatures inside the greenhouse are often 11°C higher than outside. Adverse effects on plants from excessive heat include reduction of flower size, delays in flowering and loss of stem length.
Most plants prefer the air temperature between 15 and 24°C. Maintain a constant day temperature 3-6°C above the daily minimum and allow a 6°C fall at night. Summer cooling requires large volumes of air be brought into the greenhouse and pass through the entire plant zone. Air conditioners are not recommended, as the air is very dry and unsuitable, except for the production of mushrooms.

Moisture and Misting

If intermittent sprays of water mist are applied to the top of cuttings, a temperature differential develops between the root and leaf zones. If the root zone can be kept warmer than the leaf zone, there is a tendency towards greater growth in the root zone. In other words, the warmest part of the plant will grow the fastest. In addition, the increased humidity created by the misting reduces water loss from the cutting. 

Misting systems generally have a solenoid valve between the water source and the misting system which remains open to ensure that cuttings never dry out. When electricity is applied the valve is closed and water is shut off. The solenoid valves are generally controlled by the following mechanisms.