What are the maximum light and CO2 levels that can be applied to a plant before destroying it? Please take into account that limiting factors are all under control.

Thanks for writing in. That is a good question. Let’s first look to the sun for some information. The sun is the Earth’s grow light and produces more than 100,000 lux, or roughly 10,000 lumens, per square foot. This can be even higher when under direct sun. Lumens are a measure of the amount of light cast on one square meter. Most styles of artificial lighting do not provide anywhere close to that, but more important than lumens, which refers to the amount of visible light, is the amount of usable light. Plants see light differently than we do. They utilize much more of the red and blue spectrums of light, which the human eye is not as sensitive to.

Plants use light during the process of photosynthesis. For this reason, it is important that your grow lights produce light waves in the wavelength ranges that are useful for plants, primarily the 400-700 nanometer range. Most lights cover all spectrums, but some are manufactured to produce light in certain spectrums more than others. Let’s go back to lumens and how much can be used. Illuminance is the way most growers judge their light. Most agree that ideal light levels fall somewhere in the range of 30,000-60,000 lux for vegetative growth and between 50,000-80,000 lux for the flowering stage. Serious plant problems surface at light levels above these, not to mention heat.

CO₂, which is also involved in photosynthesis, is also essential for plant growth but there is a threshold of how much your garden will use. Ambient levels of CO₂ hover around 400-500 ppm. When you increase that level to around 1,000-1,500 ppm, you will see an increase in your yields and your plants will be much healthier. If the level is allowed to rise to 2,000 ppm or higher, you will begin to see negative effects such as CO₂ burn. It is best not to allow your CO₂ levels to increase this high. Doing so not only hurts your garden but wastes CO₂ and money. As far as your choice of products, I would suggest using an all-natural form of CO₂ production versus a propane burner system or a tank system. The burners create heat and require the use of fossil fuels and tanks are cumbersome and must be re-filled often.

You should supplement your garden with CO₂ during both the vegetative stage as well as the flowering stage. If you encounter high temperatures, CO₂ will help your plants tolerate the high heat. In some instances, it may be what saves your garden from disaster.