For millions of years, the world’s flora has been releasing oxygen as it absorbs carbon dioxide through its stomata. The whole time it has existed, carbon dioxide, CO2, has been part of the basis of healthy plant life on Earth. It is no wonder then to see why some growers would want to make sure that their plants have an abundance of this vital gas.
While CO2 has been demonized in some contexts due to its congregation in the atmosphere contributing to climate change, it is still at the core of plant needs. When used correctly, it can lead to healthier plants and bigger yields without contributing to global warming. Plants are an excellent “sink” for absorbing CO2. Let’s look at the ways that CO2 benefits plants and how to increase yields by using it properly.
How Plants Use and Benefit From Carbon Dioxide
In case it’s been a few years since the botany chapter in your high school biology class, here are the basics:
- Plants capture light and turn it into energy through the photosynthesis process.
- Plants take the captured light, to convert CO2 and water (H2O), into the carbohydrates they need to grow.
- Without a supply of CO2, plants will grow until they have exhausted their carbohydrate stores and then they will stop growing. Conversely, too much CO2 will stop the photosynthesis process.
That may be an oversimplification of the varied processes that go into each step and all of the other nutrients involved, but in a nutshell, that is how plants make their own food with light, CO2, and water. Carbon dioxide is as important to plants as oxygen is to us and other animal life.
Plants “breathe” in CO2 through a process known as respiration. Tiny pore-like holes in the leaves (stomata) open and close through guard cells that operate by using water pressure. When these miniscule holes open, Oxygen and excess water diffuse out while CO2 diffuses in. The carbon dioxide then enters cells known as chloroplasts where the captured sunlight and CO2 combine to form the sugars that the plants use as food to fuel their other biological processes.
So, plants grow better with additional CO2. Most of the increased growth speed and size is gained when growers add CO2 during the vegetative stage, but even afterwards, CO2 supplementation can help. Growers not only realize added crop productivity and yield improvements (up to 20 percent more growth and yields) with additional carbon dioxide, but there are other benefits that extra CO2 can give to a grower’s crops.
Crops that have been given higher levels of CO2 are better able to handle stressors in the environment. For growing setups with heat producing grow lamps or in growing environments that tend to be on the hotter side, plants growing in air with between 1000 and 1500 parts per million of CO2, can still grow in temperatures as high as 86-95 F (30-35 C). For growers of cannabis crops who need to be discreet, CO2 generators in a grow room are able to mask the smell of blooming cannabis. This is because carbon dioxide injection methods (more on the below) work best in a sealed environment without air leaks. These generators burn natural gas to produce CO2 which has its own smell which can cover up the smell of cannabis.
Optimal Levels of CO2
There is no one, single level of CO2 that is ideal for a particular crop. In a typical indoor space, with “normal” ventilation and access to fresh air, the CO2 level should be about 400 parts per million (ppm). This is comparable to CO2 levels that plants would find growing outside.
Growers who intentionally plan for increasing CO2 levels for their plants, have achieved great success in their crop health and yields with carbon dioxide levels between 1200 and 1500 ppm. The key here is to make sure that the plants can use it all. Increases in CO2 must correspond with increased amounts of lighting.
There is a formula that growers use to determine how much CO2 their growing space needs. Take the room length, multiplied by the room width, multiplied by the room height to get the cubic area. Then, take that number and multiply it by 0.001. For example, assuming that the growing space is starting at about 400 ppm of CO2, and that the growing space is about 13’ (4 M) by 13’ by 10’ (3 M) or approximately 1700 Cubic feet in area (48 cubic meters), about 1.7 cubic feet (.48 cubic meters) of CO2 gas needs to be added to raise the ppm of CO2 to 1000. For additional calculating resources, visit https://www.hydrotekhydroponics.com/calculators.
As mentioned, increasing CO2 levels must happen in concert with raising light levels. For an average ppm of 400 for CO2, lighting output in your growing area can be as low as about 12,300 lux/lumen (1150 foot candles). On the other extreme, growers looking to achieve up to 1500 ppm of CO2 need to have light output at 80,400 lux (7500 fc). In between, a ppm of 600+ requires lighting with 49,300 lux/lumen (4600 fc) and a ppm of 1200-1300 needs 59,200 lux/lumen (5500 fc).
Managing CO2 Levels
Once you have decided that CO2 is the way to go to give your plants that boost in growth and yields that you need, it is important to consider how best to deliver that to them. Regardless which method you choose, it is important to get some type of a CO2 monitor. As you will see, several methods of delivering carbon dioxide to your plants are difficult to quantify. Having the monitor will let you know if the chosen method is making a difference or if levels are getting too high and need to be adjusted.
Systems
There is a CO2 system for every budget and every space. From low tech, DIY solutions to higher-end CO2 controllers and generators, any space can accommodate one of these solutions. Resources, available space, and needs will dictate what works best in each situation.
Low-tech solutions include such common household or garden items such as baking soda, vinegar, and compost. Other relatively inexpensive ways to boost CO2 include dry ice and CO2 bags.
For each low-tech solution there are of course pros and cons:
- Baking soda and vinegar: These materials when combined release carbon dioxide. They are cheap, readily available and their use does not increase temperature. Unfortunately, the amount of CO2 released is hard to assess, and the effects of the chemical reaction are short lived. If a quick burst of any amount of CO2 will do the trick, this is a good solution. It is not, however, a good plan for long-term success.
- Fermented yeast: This is another good way to cheaply release an unknown amount of carbon dioxide into a growing area. The same type of yeast used in baking will result in a small amount of CO2 release, with little effort. On the down side, it can start to smell bad after a while and it would only really have some impact in a small growing area.
- Compost: Another method to get smaller and unquantifiable amounts of carbon dioxide is to keep buckets or bags of actively composting material. As it starts to break down, CO2 is released. Another plus is that it can be used as a fertilizer. Like yeast, it too can start to emit unpleasant odors. It can be a free source of CO2 when using food scraps, but as long as it is decomposing, CO2 will keep being released, so there is no way to “turn it off” if you do happen to reach the maximum amount of CO2 your space can handle.
- Dry ice: Not so commonly available, but still relatively inexpensive, dry ice is solid carbon dioxide that turns into the gas form of CO2. Using dry ice does not increase temperature or humidity. It cannot be stored though. It has to be used right away upon receiving it and there is not any way to really control the flow of it. It, too, is not a long term solution. While it is relatively cheap in the short term, there are more cost-effective methods that will do a better job.
- CO2 bags: CO2 bags rely on fungi to release enzymes to digest substrate which will release CO2 in the process. This environmentally-friendly option to release CO2 does require a large volume to make any kind of significant impact though on carbon dioxide levels in a growing area. These are often paired with a CO2 monitor, to know when to replace the bags.
For larger, and especially commercial growing setups, where it is important to be more precise with releasing specific amounts of CO2, there are more sophisticated options. CO2 tanks and controllers, along with CO2 generators, are two of the more commonly employed systems to increase CO2 levels in a growing facility.
Carbon dioxide tanks and controllers are widely used in many greenhouses. They do have a high cost on the front end, but can release controlled amounts of CO2, and can be used in a tightly sealed space safely. CO2 tanks are, as the name implies, tanks, filled with CO2 gas, connected to a regulator or controller which can be set by the grower to release the desired amount. It is however possible in the event of a malfunction, for high levels of CO2 to be present which can be very harmful to humans who may unknowingly be working in the vicinity. Monitors that can be viewed remotely are critical to ensure worker safety. Use of CO2 tanks may require a special license in some regions as well.
Carbon dioxide generators utilize natural gas, or alcohol and flame to create and release CO2. Heat is a byproduct of these systems so they are most often only used in larger greenhouses and in conjunction with adequate environmental controls. They are efficient and easy to use, but not cheap. Because of the flame used, there is the potential for fire if it is not used correctly.
Techniques and Tips
Once you understand the role of CO2, how it can help growers achieve better results, and some of the methods to deliver it, what then? Using CO2 to increase yields is a practice best done once all of the other basics are covered. New growers are encouraged to learn how to get the best results with nutrients, lighting, and quality materials before experimenting with additional carbon dioxide. Supplemental CO2 works best on healthy plants that have their basic needs otherwise covered.
When it is time to start adding CO2 to your crops, it is important that it only be administered during daylight hours or during times when your plants are under lighting. CO2 should not be released during periods of darkness. It will go to waste.
The stage of growth of your crops will also dictate CO2 usage. Additional carbon dioxide helps to develop leafy growth, and to encourage bud sites. The fuller the plant, the more leaf area and the more stomata it possesses to absorb CO2. Some growers continue giving their plants CO2 into the flowering stage.
Additional carbon dioxide can help crops during the first couple of weeks of the bloom period. It does not do much to benefit plants beyond this stage as it is only useful while plants are actively growing and developing.
The position and placement of the CO2 emitters is also important. Carbon dioxide is most useful to your plants when it is directed towards the leaves. Since CO2 is heavier than air, it will sink. Whatever method of CO2 release is used, it should be placed above the canopy so that it will “fall” onto your crop. This might mean suspending your system, or it could even be placed on blocks so long as it is above the canopy of the plants. It is useful to have fans at floor level, pointed upward to also help keep the CO2 circulating around the foliage.
Precautions/Other Considerations
Adding CO2 to your growing space clearly has benefits. There are, however, several points to consider before going “all in” on carbon dioxide supplementation. First, it is important to make sure you have the right setup in order to benefit from the addition of CO2. Adding CO2 will do no good, and even cause harm if your space is not conducive for it.
CO2 is only effective in growing spaces with bright lighting, lower humidity level, and good air flow. Increased carbon dioxide will only benefit plants that are actively photosynthesizing. If your lighting setup is less than 600W/m², it is not advisable to add additional CO2. CO2 also increases humidity levels, especially in enclosed and smaller spaces. Good airflow and even dehumidification may be required to maintain optimal growing conditions when adding carbon dioxide.
Higher humidity levels can invite fungal and mold problems. It is critical that growers who add CO2 keep a close watch on this and make sure that there is good circulation around all of their plants. Too much CO2 is a bad thing. Besides setting the stage for mold, mildew and fungi, excess carbon dioxide can be harmful to humans and the environment. It is of utmost importance that growers who opt to use CO2 for the benefits it can provide to crops and yields, strictly monitor light, humidity, and CO2 levels to ensure that they are getting the full benefit of the extra CO2, but none of the potentially harmful side effects.
In regards to cost, this is not an area to be frugal. Cheaper CO2 systems are not effective and can increase operating and energy costs due to their inefficiencies. Quality CO2 setups cost more initially, but will pay dividends in the long run.
