Do Marijuana Plants Need Oxygen?


The short answer is ‘yes,’ of course, but there is a lot more to it than that! It is easy to dismiss the importance of oxygen when growing cannabis. After all, dry air contains approximately 20.95% of it, so your plants are okay, right? Even at 100% relative humidity, the atmosphere consists of 20.4% oxygen. However, if you don’t allow for excellent air circulation in the grow room, your plants could suffer.

Cannabis & Respiration

Respiration is the act of breathing. Like every other living organism, plants respire. While their needs are less complex than humans, they still require a well-ventilated growing area to thrive. Your cannabis plants use their roots, stems, and leaves, in the process of aerobic respiration. They use oxygen as an oxidizer. Dark respiration does not depend on light, whereas photorespiration does.

It is a 24/7 process but is more intense at night because of the cessation of photosynthesis. In case you wanted a quick recap, here is what photosynthesis looks like:

  • The plant draws water through its roots.
  • The leaves take in carbon dioxide (CO2) from the air and trap energy from the sunlight.
  • Next, the plant uses the sun’s energy to turn water and carbon dioxide into sugars and oxygen.
  • The plant releases the oxygen into the air and uses the sugars to grow.

Without photosynthesis, the depletion of oxygen in the atmosphere would occur within a few millennia. As you can ascertain from the information above, photosynthesis involves several processes. This is the reason why plants have a higher respiration capacity at night. It is also why every marijuana growing guide you have read tells you to keep the night time temperature lower than during the day.

Another reason why cannabis plants need air is due to the CO2 levels it provides. Today, the level of carbon dioxide in the atmosphere is around 407 parts per million (ppm). For the record, it is the highest level in the last 800,000 years! Elevated CO2 is not suitable for humans, but plants thrive on it. Ideally, your grow room will contain a carbon dioxide level of between 1,000 and 1,400 ppm.

Other Important Components of Respiration

It is also essential that you keep the substrate and roots well oxygenated. Growers who use organic soil need an even higher level of oxygenation because the microorganisms in the earth also require oxygen. The porosity of your substrate also impacts the respiration capacity of the soil. Improve matters by adding perlite or coco noir to your soil mixture.

Your marijuana plants contain a myriad of tiny pores called stomas. Think of these as the plant’s ‘nostrils,’ which they use to absorb CO2 and release oxygen. If you find most of the stomas on the underside of the leaves, spray both sides with water twice a day. The ideal temperature of the water is between 65- and 70-degrees Fahrenheit. Stomas are minuscule and get clogged easily, so regular cleaning is required. Outdoor growers don’t have this problem as rainfall does the work for you.

During photosynthesis, your crop absorbs CO2 and releases O2. At night, it absorbs O2 and releases CO2. If you grow your herb outdoors, you have automatic air circulation. Indoor growers, on the other hand, need to invest in well-placed fans or a ventilation system. An intake fan is also necessary to bring in fresh air, and an exhaust fan to remove stale air.

Why Air Circulation Is Crucial

Constant air exchange is the key to a successful indoor grow. The three things to worry about are:

  • Clean stomas
  • Good air circulation
  • Consistent air exchange

Don’t forget that even distribution throughout the entire room is a prerequisite. Otherwise, you will end up with areas featuring stagnant air. It is a balancing act because you must ensure the air is neither too moist nor too dry. We recommend avoiding air layers because hot air gathers in higher areas, while cooler air usually flows downwards. The result is a slower growing crop that is more susceptible to insect infestation and mold growth.

Useful Air Circulation & Exchange Equipment

The following is not an exhaustive list, nor do you need to buy all of it. Your needs depend on the size of your grow room. If you have a small grow tent, for example, there is no need to buy half a dozen items from this list!

  • Intake Fan: Brings oxygen-rich air to the growing space.
  • Exhaust Fan: Removes air that is low in oxygen.
  • Active Carbon Filter: A necessary purchase if you grow stinky weed and don’t want to attract attention!
  • Ventilation Ducts: You can purchase ducts to remove stale air and others to allow fresh air in.
  • Acoustic Box: Reduces the noise caused by the fans.
  • Ceiling Fan: As the name suggests, you suspend this fan to your grow room’s ceiling, ideally between the lamp and the tops of your plants. A ceiling fan helps cool down the layer of hot air that accumulates in that region.
  • Clip Fan: A smaller fan that is ideal for small tents.
  • Oscillating Stand Fan: Allows for even air distribution.
  • Floor Fan: Helps recirculate the area near the floor. In general, only those with a large growing area need this device.
  • Dehumidifier: Helps reduce the humidity in a room.
  • Humidifier: Increases the level of humidity in a room.
  • Thermohydrometer: Measures a room’s temperature and humidity.

Boost Yield with Dissolved Oxygen

Dissolved oxygen (DO) relates to the level of oxygen saturation in the water. The more O2 in water, the better off your marijuana plants’ roots are. The process of a plant exhaling water vapor, oxygen, and nutrients via the stomata is known as transpiration. It enables your plants to cool down, alters osmotic pressure in cells, and ensures a steady flow of water and nutrients up from the root system.

When your weed’s roots are in an environment with lots of oxygen, they are more efficient when absorbing nutrients. O2 helps provide the metabolic energy needed for nutrient uptake. When you expose cannabis’ roots to high levels of oxygen, you benefit from greater root mass and healthier root tips.

A lack of oxygen in the root system reduces the rate of water and nutrient uptake. The result is a reduction in plant growth, and occasional wilting due to heat stress. Throw in a lower level of photosynthesis and decreased glucose transfer abilities, and your crop has a lot of problems!

We haven’t even mentioned the enhanced production of ethylene. This flammable hydrocarbon gas could cause cell collapse, and increase the risk of disease. If that isn’t enough, you also have a calcium shortage to contend with. In a nutshell: Less oxygen = lower transpiration = bad news!

How Much Do You Need?

First and foremost, the only way to measure dissolved oxygen is to purchase a special DO meter. Most growers know how vital pH and EC are, and have no issue buying a device to measure those readings. However, you can purchase a pH or EC meter for no more than $30. In contrast, a DO meter can cost up to $300! It is also much harder to use and often requires watching videos to know what the hell is going on.

Water in a low-pressure boiler typically has a dissolved oxygen rate of no more than 2.0 ppm. However, boiler plant operators try to keep it below 0.01 ppm. In tap water (at room temperature), the DO level rises to perhaps 5-9 ppm. According to most experts in the field, you only notice a difference at a rate of 12+ ppm. Research by the University of Wisconsin and the University of Minnesota suggests that plants utilize nutrients effectively when the DO in water is 10 – 12 ppm.

Charlie Hayes has a biochemistry degree and is the owner of Advanced Treatment Technologies. His company specializes in providing water treatment solutions. During his research, he found that any health and production benefits in marijuana reach a plateau at a DO rate of 40 – 45 ppm in the root zone. However, you need to begin with a far higher concentration in a treatment system to deliver the right amount to the roots.

Increasing the Water’s Dissolved Oxygen Level

There are several methods of increasing DO levels in the water. Aeration of water through the use of a bubbler is the most popular way. The process involves injecting air in the water. However, you must pay attention to Henry’s Law. It states that the solubility of gas is controlled by concentration, temperature, and pressure. For instance, CO2 is 20 times more soluble than oxygen.

Hayes asserts that the use of ozone is the most effective method of getting DO into the water as it is 12.5 times more soluble than oxygen. You need a treatment system capable of handling a high concentration of ozone before you use an ozone generator. The system must also have the ability to mix the molecule properly and hold it in the solution. As Hayes states, ozone is unstable with a half-life of as little as 3-5 minutes when converted to DO.

If you use a hydroponics system, another option is to place a stirring pump at the bottom of the reservoir attached to minimal tubing. It mixes the solution on a timed cycle or continuously. The process is akin to how the water in the oceans keeps moving due to the work of currents. When you mix or move water, you enable the already dissolved oxygen to remain stable. You also see an increase in DO because the water mixes with air on the reservoir’s surface.

Growers also use hydrogen peroxide, but it could result in a level of toxicity that ultimately harms your plants.

Don’t Forget the Water’s Temperature!

The roots of your marijuana plant will decrease metabolic activity when exposed to temperatures below 60 degrees. The so-called sweet spot is between 62 and 66 degrees. Don’t allow the temperature of the root zone to go above 75 degrees, or else you risk root rot.

Fully oxygenated water at a temperature of 68 degrees could hold a DO level of up to 9 ppm. The same water at 86 degrees has a DO level of just 7.5 ppm. Therefore, it makes sense to use room temperature water when feeding your plants.

Final Thoughts on Marijuana Plants & Oxygen Levels

Ultimately, your crop should grow just fine without the need for increased dissolved oxygen levels in the water. However, advanced growers know that increasing the DO in the water they provide to their plants is a difference-maker.

While it may not make sense to spend heavily on dissolved oxygen increasing equipment or a meter to read the level, it is a worthwhile investment if you intend to grow commercially. When your roots receive water with a heavy dose of DO, your plants will feel refreshed and energized. The result is faster growing and healthier weed, along with an increased yield.