Chapter 8

Carbon Dioxide in Greenhouses

(book excerpts)

The growth and health of plants is the result of the photosynthesis process in which the energy of the sun is used by the plant in combination with carbon dioxide (CO2) and water to synthesize organic matter, while giving off oxygen. Consequently, carbon dioxide is one of the three major components responsible for plant growth. Carbon dioxide is present at a concentration of approximately 340 ppm in the atmosphere. However, this is an average and the actual concentration in a given location can vary. Climatic changes can cause a four to eight percent variation in carbon dioxide concentration daily or seasonally due to increases or decreases in solar radiation, temperature, humidity, and the passage of storm fronts. In a greenhouse filled with plants, carbon dioxide concentration will closely follow ambient outside concentrations during the day as long as ventilation is provided. Carbon dioxide concentrations rise during the dark period because plants are not using carbon dioxide for photosynthesis and respiration by plants. During light periods in which ventilation is not required, carbon dioxide levels may fall below ambient level, especially in tightly sealed greenhouses. During the winter, carbon dioxide levels can easily drop below 340 ppm to 150 to 200 ppm during the sunlight hours, which has a significant negative effect on the crop. Ventilation during the day can raise the carbon dioxide levels closer to ambient but never back to ambient levels of 340 ppm. An extremely low carbon dioxide level of around 100 ppm will completely prohibit carbon dioxide uptake and growth. Depletion only occurs at daytime, caused by photosynthesis (CO2 uptake which requires light). Supplementation of carbon dioxide is seen as the only method to overcome this deficiency and increasing the level above 340 ppm is beneficial for most crops. Increased carbon dioxide levels will shorten the growing period (5 to 10%), improve crop quality and yield, as well as, increase leaf size and leaf thickness.

Click on the following topics for more information on carbon dioxide in greenhouses.

Topics Within This Chapter:

  • Carbon Dioxide Supplementation in Greenhouses
  • Advantages and Disadvantages
  • When to Supplement with Carbon Dioxide
  • Recommended Carbon Dioxide Concentrations
  • Sources of Carbon Dioxide
  • Carbon Dioxide Generators
  • Boiler Stack Carbon Dioxide Recovery Systems
  • Liquid Carbon Dioxide Supplementation
  • Control of Carbon Dioxide Levels in the Greenhouse