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Understanding The Functions of Cannabis Stomata

Cannabis stomata

Experienced growers know that cultivating marijuana requires skill and detailed knowledge. Scientific terms like cannabis stomata may seem daunting at first, but it’s crucial to your plants’ development. 

What role do stomata play in growing marijuana? Knowing this is the first step to improving your crops’ wellbeing. If you can control these tiny pores, you’re well on your way to cultivation success. 

Join us to uncover the factors that influence the opening and closing of stomata in plants. 

We also highlight the role of these small openings in photosynthesis and how you can manipulate them to benefit your final yield. Let’s get started by understanding the meaning of stomata. 

Cannabis leaves
Cannabis leaves

What are cannabis stomata?

When we refer to the stomata of cannabis, we’re discussing themicroscopic openings on the leaves of marijuana plants. They’re also sometimes referred to as stomates and singularly as a stoma.

These small organs play a crucial role in the daily functioning and, subsequently, overall crop health. To fully grasp the stomata definition in plants, we should view them as mini two-way tunnels—carbon dioxide enters while oxygen and water exit

The stomata structure on cannabis has a small opening for each stoma and two guard cells (one on either side). They also have auxiliary cells surrounding them. 

What are guard cells

For a mental visualization, compare guard cells to a pair of lips on a mouth. They act as windows to the plant and control whether the pores are open or closed. They’re permeable and can absorb or release water to change their size through the process of osmosis

During the light cycle for weed, the cannabis stomata guard cells use potassium and sugars to help with water absorption. The auxiliary cells assist with attracting adequate potassium to the region. When there’s enough water in the cells, they open. These pores close during the dark cycle and if the water loss is too high. 

How do stomata work

You might be wondering when the stomata open and close and how they work. The answer lies in the environment. Certain stimuli trigger the guard cells to increase water absorptionand open, whereas others result in stomata closure on cannabis plants. Environmental conditions like light, humidity, and access to CO2 all affect the position of the pores.

When they’re open, they absorb carbon dioxide, simultaneously releasing water and oxygen. They play a vital role in photosynthesis due to their relationship with light, moisture, and CO2. The importance of stomata is clear when we look at the functions it performs. 

There’s a fine line between accessing sufficient CO2 for cannabis and losing too much moisture. Keep this in mind when you alter the environmental factors to manipulate the cannabis stomata. 

When do stomata open and close 

Several environmental conditions impact the position of these microscopic openings. Depending on the trigger, cannabis leaf stomata can close within minutes or hours. When are stomata open on cannabis plants? Most of the time, light exposure initiates the pores to open. Well-hydrated plants with sufficient nutrients perform this function optimally. 

When a crop lacks water or potassium, the guard cells close the opening, and so does excessive CO2. This action prevents further moisture loss from the stomata, and cannabis gas exchange stops when they close. 

To encourage the stomata to open, ensure you use the proper techniques for watering weed. Don’t allow them to dry out, but resist giving too much H2O as it can also be detrimental. Humidity levels also play a role, with dryer conditions causing closure and higher ranges facilitating better gas exchange. 

Structure of stomata
Structure of stomata

Where are stomata on cannabis leaves

The location of stomata in plants is the leaves. They’re so small that you can only view them using a magnifying glass or microscope. Where are the stomata on cannabis foliage? They form on the underside of marijuana crop leaves

The position of the pores on the weed leaf is an adaptation of most dicotyledonous plants. It reduces light and heat exposure. As a result, the plant loses less water.

What is the importance of stomata 

The cannabis stomata perform several functions, all of which contribute to the health of the marijuana plant. Below we look at each role in detail. 

Carbon dioxide

The most essential function of cannabis leaf stomata is absorbing CO2. They need to take in large quantities for photosynthesis to occur optimally.

When enough gas is present (when the stomata are open), the plant flourishes. If there’s too little, growth slows. Excess CO2 also causes the pores to close.

Water vapor and humidity

Open stomata on cannabis mean that water vapor escapes. It happens because the plant needs to balance the fluid loss with the gains of CO2 absorption. 

When it loses too much H2O, the stomata close. It retains moisture but no longer takes in the beneficial gas. High temperatures also increase the rate of respiration. Cannabis stomata stay open longer when the humidity levels are around 50–60%. 


As part of the photosynthesis process, cropsgive off oxygen as a waste product. The stomata release this gas and water vapor. In some cases, a closed opening leads to an imbalance of gasses within the plant, and inefficiencies occur.

Light and dark cycles 

Light is one of the most crucial environmental stimuli. The cannabis stomata respond by opening, and the plant takes in both light and carbon dioxide. Certain colored lights help manipulate the time the pores open but exercise caution. Tinkering with the light/dark cycle of cannabis crops can cause problems.

When it’s dark, the cannabis stomata close—photosynthesis stops. Autoflowering plants won’t be impacted severely by sudden light changes, but photoperiod crops will. 


When the cannabis leaf stomata are open, it allowsheat to escape by releasing water vapor. When it’s too hot, plants release more moisture, and to avoid dehydration, the pores close. 


Marijuana plants require macro and micronutrients to thrive. While most of the absorption occurs through the roots, when growers use foliar sprays, they enter the cannabis stomata.

The guard cells also use some of these nutrient solutes to absorb water when they open. If there isn’t enough and the plant has a deficiency, it affects the crops’ ability to function properly. The cannabis stomata also won’t open as needed, and CO2 intake drops.

Water on weed leaves
Water on weed leaves

What is the role of the stomata in photosynthesis

For photosynthesis to take place, plants need access to water, sunlight, and CO2. The byproducts of the process are oxygen and food. The cannabis stomata are responsible for the flow of gasses in and out of the leaves. 

This exchange occurs mostly during hours of light and stops when darkness falls. Water vapor also escapes through the opening, and when the plant loses too much, the cannabis stomata close.

These minuscule pores don’t participate directly in photosynthesis but regulate the gas exchange. If the plant doesn’t get enough carbon dioxide, the process can’t occur. On the other hand, the crops can dehydrate should too much water escape.

The cannabis stomata work to keep a delicate balance between these factors. 

How to control cannabis stomata 

As a grower, you can manipulate the position of the cannabis stomata by altering the environmental factors. It’s crucial to note that each of these is interrelated, and by making changes, you impact the entire balance. 

The table below gives an overview of how these changes work. 

FactorsChange implementedEffect on the stomataEffect on other environmental factors
WaterAn increase or decrease of water supplied to the plant.Water is essential for photosynthesis. Some growers water sparingly, which causes the cannabis stomata to close to prevent losing water vapor.
Ensure that the substrate is always moist (not soaked) so the stomata can stay open during light hours.
If the stomata close to preserve water, it can’t take in the required CO2. This hinders the process of photosynthesis.
Grow room humidityRaising the humidity levels.When the grow area is dry, the pores don’t open, and the guard cells lose moisture faster. Increasing the humidity levels to range between 50–60% allows the gas exchange to take place while using less H2O.If the relative humidity is too high, it can invite pathogens like mold and mildew. It can also lead to bud rot.
Carbon dioxideAn increase in carbon dioxide.The cannabis stomata need to absorb plenty of CO2 while minimizing water loss. Supplement your crops with up to 1500 PPM of carbon dioxide. Exceeding these levels causes the stomata to close.If there isn’t enough CO2 present, photosynthesis can’t take place. This affects bud production and quality.
TemperatureAn increase or decrease in temperature.When the temperature is too high or too low, the stomata close to preserve the plant. In moderately warm temperatures, the cannabis stomata open to allow the leaves to cool down.Excessive heat can burn the leaves. A range of 65–80℉ is best.
LightLight and light color stimulation.The main trigger for these pores to open is light exposure. By using blue light, the cannabis stomata reactions are more evident. Experienced growers use these color LEDs to manipulate stomata mechanisms at the risk of moisture loss.If you’re not careful, you can negatively affect the plant’s balance and lose too much water.
Weed stomata
Weed stomata

Sealing off stomata

Cannabis stomata play a vital role in ensuring that the plants receive enough CO2. They also balance how much H2O is lost during the process. Light, humidity, and temperature also affect the position of these tiny pores. 

These openings function at their peak when your grow room conditions are optimal. Ensure appropriate lighting, temperature, and humidity levels for healthy plants. Implement proper watering techniques and don’t over-supplement with CO2. 

An efficiently maintained grow space helps the cannabis stomata maintain the perfect balance. If you’ve found this information useful, why not share it on social media, and subscribe to our newsletter? Check out the Homegrown Cannabis Co. seed store for more cannabis-related information and growing tips.

About the author: Derek LaRose

Also known as Kronic from The Cannabis Kronicles, Derek LaRose is a young ambitious cultivator and a staple educator for indoor cultivation.

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