(7) How to successfully operate a commercial  greenhouse!

Most of the following discussion applies to large commercial greenhouses with the investment to produce on a large scale, but small greenhouses and the humble cloche count benefit from the same factors too!

So the various factors can be manipulated to increase the rate of photosynthesis and hence increase plant growth.

Summary so far to help increase crop yields

 

Greenhouse design/operation and the photosynthesis light intensity factor

• Lots of glass window panes to let light in.

• Site the greenhouse in a non-shaded area.

• At night artificial light can be supplied.

• However, the light level with have its limit (either sunlight or artificial light at night), so for maximum effect you may still need a warm temperature and a fresh supply of carbon dioxide.

 

Greenhouse design/operation and the photosynthesis temperature factor

• Ideally in greenhouses you would want the optimum temperature, a constant adequate supply of carbon dioxide and plenty of light - hence the use of transparent glass!

• A greenhouse warms up by trapping the heat radiation from the sun - the 'greenhouse effect'.

• BUT take care that the greenhouse does not get too hot eg by opening ventilation systems or putting up shades.

• In cold weather, heaters might be employed in a greenhouse because the temperature may be too low for efficient photosynthesis for plant growth - but heaters increase cost of production.

• If the heaters are not electric and burn a fuel like paraffin, then lots of carbon dioxide is produced - quite handy, two factors catered for at the same time!

 

Greenhouse design/operation and the photosynthesis carbon dioxide level factor

• If the ambient temperature is warm and the plants/greenhouse in bright sunshine, the limiting factor might be the concentration of carbon dioxide in air.

• You do need some ventilation or the level of carbon dioxide gas will fall if the air is not replenished as the carbon dioxide is used up by the plants.

• BUT, for maximum effect you need a warm temperature, plenty of light and extra CO₂ if you can supply it!

 

Overview of operating a successful greenhouse - commercial or amateur grower!

 

A greenhouse used is to artificially create the best environment for growing plants and increase photosynthesis efficiency.

ventilation - need to keep the air fresh and ensure the carbon dioxide level doesn't fall below that in the air outside.

glass (or transparent plastic) panels - allows the transmission of visible light for photosynthesis and infrared radiation to be absorbed and raise the temperature.

carbon dioxide supply - can artificially increase CO₂ available to plants to increase rate of photosynthesis.

water supply - plants need a constant supply of water, the soil or compost may get to dry for optimum plant growth and the higher temperatures in a greenhouse increase the rate of transpiration.

heater  - electric to raise temperature on colder days, preferably from renewable source, if paraffin, the combustion produces CO₂ so that helps increase the rate of photosynthesis.

artificial lighting - enables photosynthesis to be continuous 24/7 and independent of the weather, BUT you need periods of darkness (use a timer) to allow the plant to transport and store glucose as starch.

humidifier - if the atmosphere becomes too dry the rate of transpiration increases and plants may droop from lack of water

blinds - can be used to control the light if necessary.

thermostat - not sure if this is used in greenhouses?

 

Growing crops in greenhouses can significantly increase the crop yield for a given area.

Greenhouse horticulture (agricultural growing of flowers, fruit and vegetables) is an intensive farming method using various technological developments - this particularly applies to hydroponics - method of food production,

ideally farmers-horticulturalists want optimum yields of crops without excessive leaf or root production.

A greenhouse traps the sunlight energy raising the internal temperature to make it less of a limiting factor but heating may be required in winter.

However, the extra costs of heating, artificial lighting or adding CO₂ to the air, must be off-set by selling an acceptable quality product at a sustainable market price that the consumer is prepared to pay!

You can increase the temperature and carbon dioxide levels at the same time by using a paraffin heater - one of the better uses of a fossil fuel when burned to form carbon dioxide!

In summer it might get too hot so extra shade and ventilation may be needed to create cooler conditions.

Using artificial light extends the growing period beyond normal daylight hours - but an extra cost.

You should also note that plants enclosed in a greenhouse are less susceptible to pests and diseases.

For more see sections on plant diseases and pest control

 

Fertilisers may be added to the soil to provide the minerals the plant need's and absorbed from the soil by the root system.

 

Using greenhouses enables market gardeners to produce more good crops per year and if you can control the conditions and efficiently produce a reasonable quality crop - then your business can be commercially successful.

Large scale greenhouse complexes are proving successful in using artificial growing conditions and employ light and heat controls.

See also Food security - population growth and sustainability issues   

and in particular growing food using hydroponics

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Key points - managing photosynthesis in the context of growing crops in a greenhouse

Source of information is based on textbooks and syllabus-specifications for students taking the AQA GCSE, Edexcel GCSE and OCR GCSE level biology examinations (~US grades 9-10)

Controlling Photosynthesis in a Greenhouse

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Reminder of the 3 Main Limiting Factors of Photosynthesis

Light Intensity, carbon dioxide concentration and temperature

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1. Light Intensity

• Light provides energy for the photosynthesis reaction.

• Greenhouses often use artificial lighting (lamps/LEDs) to:

  • Extend daylight hours.

  • Supplement natural light on cloudy days.

• Lamps may be set on timers to match plant needs.

Increased light speeds up photosynthesis until light is no longer the limiting factor.

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2. Carbon Dioxide Concentration

• CO₂ is a raw material for photosynthesis.

• Growers can increase CO₂ levels by:

  • Using paraffin heaters (which release CO₂ as a by-product).

  • Releasing compressed CO₂ gas directly into the greenhouse.

• CO₂ enrichment can significantly improve growth when combined with optimal light and temperature.

Too much CO₂ won't increase the rate if another factor becomes limiting.

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3. Temperature

• Photosynthesis is enzyme-controlled, so temperature affects enzyme activity.

• Greenhouses maintain ideal temperatures (around 25–30°C) by:

  • Using heaters in cold weather.

  • Ventilation or shading in hot weather.

• Thermostats and automatic systems help prevent overheating or chilling.

If it's too cold, enzymes work too slowly; too hot, enzymes denature.

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4. Water Supply

• Water is another essential reactant for photosynthesis.

• Commercial greenhouses use automated irrigation systems:

  • Maintain constant moisture levels.

  • Prevent drought stress or waterlogging.

• May be combined with nutrient solutions (hydroponics).

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5. Chlorophyll Levels

• Healthy leaves with enough chlorophyll are vital for absorbing light.

• Growers prevent deficiency by:

  • Supplying minerals (especially magnesium) through fertilisers.

  • Preventing disease and pests.

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The Role of Technology in Greenhouse Control

Modern glasshouses use computer systems and sensors to monitor and adjust:

• Light levels (via blinds and lamps)

• Temperature (via heating and ventilation)

• Humidity and water supply

• CO₂ concentration

This ensures optimal growth all year round, increasing productivity and reducing waste.

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Why This Matters for Biology

• Demonstrates practical applications of photosynthesis knowledge.

• Links biology to agricultural technology and food production.

• Prepares students for data analysis, graph interpretation, and extended answer questions.

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Exam Tips

• Be ready to describe and explain how each factor affects photosynthesis.

• Use phrases like “limiting factor”, “controlled environment”, and “commercial optimisation”.

• Practise interpreting graphs showing effects of light, CO₂, and temperature.

• Revise ways to increase crop yield using biological understanding.

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Keywords, phrases and learning objectives for this part on photosynthesis

In the context of photosynthesis, be able to describe how best to operate a greenhouse for commercially growing flowers, vegetables and salad plants.

Understand the design and operational control factors and the costs factors involved to maximise the rate of photosynthesis.

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