Raising and cultivating ornamental and edible plants in greenhouses enables nurseries and farms to produce their products independently of the season and with consistent quality. The primary goal in greenhouse cultivation is to provide ideal growing conditions by optimally regulating climatic conditions, and increasing productivity as a result. In addition to the right humidity and temperature, plants need carbon dioxide to flourish. Higher yields can be achieved by artificially increasing the CO₂ concentration in the greenhouse, especially for vegetables. This offers greenhouse operators an enormous competitive advantage compared to outdoor cultivation.

Carbon Dioxide Promotes Plant Growth

Plants use photosynthesis to produce glucose, which they need to grow. The "basic ingredients" for this biochemical process are light, water and carbon dioxide.
If plants cannot access enough CO₂, they produce less glucose and grow more slowly. Conversely, more CO₂ has a positive effect on plant growth. A high CO₂ concentration makes plants grow faster, promotes root formation, and ensures earlier flowering and higher yields. 

Therefore, in greenhouses the CO₂ content is artificially increased by what is known as CO₂ fertilisation (or CO₂ fumigation). This can significantly increase the productivity and quality of the cultivated plants. Especially in the low-light season, CO₂ fertilisation is useful because it also enhances the effect of artificial light and thus counteracts the natural lack of light.

When using CO₂ fertilisation, the CO₂ level in the greenhouse needs to be continuously measured and monitored for several reasons:
 

• Too much CO₂ has a negative impact on plant growth. If the CO₂ concentration is too high, the plants grow more slowly and do not develop as well.
• Generating and supplying CO₂ costs money. Monitoring the CO₂ content makes it possible to use CO₂ fertilisation efficiently and therefore in the most cost-effective way possible.
• In high concentrations, CO₂ can be harmful to human health and lead to dizziness, headaches, nausea and even unconsciousness. The legally defined maximum workplace concentration (MAK values) of 5000 ppm (= 0.5 % CO₂) must therefore not be exceeded. This is another reason why responsible greenhouse operators must keep an eye on the CO₂ concentration. 
   

CO₂ Measurement with CO₂ Sensors

CO₂ sensors are the means of choice for measuring the CO₂ content in the air. However, the CO₂ sensors must be able to cope with the environmental conditions prevailing in the greenhouse. 
High humidity levels, or even condensation, in combination with impurities and chemical exposure to fertilisers, pesticides, herbicides or disinfectants (e.g., hydrogen peroxide) are particularly challenging for the sensors. Condensation-related deposits on the sensing element can impair measurement accuracy and lead to corrosion. 

In order for CO₂ sensors to work reliably and stably in the long-term under these difficult conditions, they need to be carefully tested with a view to their technical suitability.

What Greenhouse Operators Need to Pay Attention to When Purchasing CO₂ Sensors:

• Do the sensors have a sufficiently wide CO₂ measuring range?
• How good is the measurement accuracy and long-term stability of the sensors? 
• What measurement principle is the CO₂ measurement based on?
• Are the sensors suitable for use in conditions with high relative humidity?
• Are the sensors resistant to dirt and chemical contamination? 
• How quickly do the sensors react to a change in CO₂ content (response time)?
• Do the sensors have an appropriately high housing protection class (IP65 / NEMA4)?
• What maintenance and calibration options do the sensors offer?
• Can the sensors be integrated into the greenhouse control system (e.g., via Modbus RTU interface)?

Besides an adequate supply of CO₂, plants need the right humidity and temperature to flourish. This is what makes it so important to also monitor these climate parameters precisely and reliably with suitable humidity and temperature sensors. This is the only way to ensure that greenhouse cultures will develop optimally and generate the desired economic success. When choosing sensors, greenhouse operators need to focus on quality and seek expert advice before making a purchase decision.

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