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7 Photosynthesis Factors You Can Influence To Maximize Your Cannabis Plants

“The goal as a grower is to be able to get that plant to produce more sugars than it will need during the day.”

– Eric Bergeron, Specialist from CANNA

Photosynthesis is a chemical process done by plants to utilize light, water, and carbon dioxide to create oxygen and sugars for various plant processes. To put it simply, your plant would not grow or fight diseases without this process. Your plants need to produce more sugars and energy than it needs within the day. This energy reserve will be your plant’s food during the late stages of development, especially bud formation to maximize your cannabis plants.

Given the basic requirements of photosynthesis, there are factors that you, as a grower, can modify or improve to make your cannabis’ food and energy-making machinery more efficient. These factors include light, transpiration, temperature, humidity, wind, vapor pressure deficit, and root pressure. Eric Bergeron, a specialist from CANNA gives advice about these factors in his session during the Growers Source Expo. 

Photosynthesis Factors You Can Influence To Maximize Your Cannabis Plants

1. Light

Photosynthesis Factors You Can Influence To Maximize Your Cannabis Plants - Cannabis-seedlings-in-pots-sunlight-shining-from-the-window
Cannabis seedlings in pots with sunlight shining from the window – Credit: Canva Stock Photos

As most growers grow cannabis indoors, Eric talks about four things that must be kept in mind about light – quality, uniformity, intensity, and operating cost. First, the quality of artificial lighting for your plants must almost mimic sunlight – with a full spectrum. There are many types of LEDs in the market, and Eric recommends those that offer those that cover as much range of spectrum as possible. Second, you have to make sure that your plants are getting a uniform distribution of light. Varying amounts of light will result in different photosynthetic rates, and those receiving less light will produce less energy. Third, a higher light intensity results in a higher photosynthetic rate. However, you must be careful not to let the leaves heat too much or it will stop transpiration and water uptake. Lastly, make sure that you monitor your operating cost. Choose a set-up that is cost-effective and efficient.

Eric Bergeron

“Cost of operation is something to keep in mind because different lights will behave in a different way.”

– Eric Bergeron, Specialist from CANNA

2. Transpiration

When-water-evaporates-at-the-cannabis-leaf-surface-it-helps-in-sending-out-excessively-absorbed-water-by-plants.
When water evaporates at the cannabis leaf surface, it helps in sending out excessively absorbed water by plants. -Credit: Canva Stock Images

The water that you let your plants drink helps transport soil nutrients to different parts of the plant. Some of the water goes out of the leaves and evaporates in the air after it has done its job. The movement of water from the roots and its evaporation through the stomata is called transpiration. When your lights are on, the temperature is high as well as the transpiration rate. A sudden shutting-off of lights will cause your room to cool down, and the moisture in the air will spike. Excess air moisture makes your plants vulnerable to diseases like powdery mildew. Go around this thing by having a system that gradually shuts off the lights. In this way, your dehumidifier will have time to vacuum out all that excess moisture in the air.

3. Temperature

Under Microscopic view of Leaf - Open vs Closed Stomata
Under microscopic view of leaf surface, stomata opens (left) when the temperature increases vs stomata closes (right) when the temperature reduces. – Credit: Shutterstock Stock Images

Stomata are entry points for carbon dioxide on the underside of the leaves. The more carbon dioxide that goes in, the higher the rate of photosynthesis for your plant. However, the stomata can sometimes close when the conditions are not right, especially when the transpiration rate is low. One of the main influences on this is the temperature. A colder temperature can reduce transpiration and can close the stomata. On the other hand, too much heat can also force your plants to become stressed. So make sure that you monitor the temperature in your facility.

“Having the leaf temperature constantly monitored in your room is very important.”

— Eric Bergeron, Specialist from CANNA

4. Humidity

Growing in a series of highly controlled rooms allows producing top-quality cannabis plants.
Growing in a series of highly controlled rooms allows producing top-quality cannabis plants. – Credit: @quest_hydro

Hand in hand with transpiration rate and temperature control is humidity. A higher temperature in your room can cause humidity to go down, which is good for your plants. However, this is not always the case. Moisture can still be high depending on the equipment that you have in the room. Therefore, humidity must still be monitored constantly because too much moisture in the air can block the flow of water from the roots to the stomata. When your stomata close up, they stop taking in CO2 needed for photosynthesis. Also, as mentioned earlier, moisture can make it easy for diseases to thrive in your facility.

Scientist Kid - Scientific Deep Dive

For those who want to dig even deeper into the science, here are greater details about chlorophyll’s role in photosynthesis.

Photosynthesis and Chlorophyll

Photosynthesis - Cannabis Leaf

Photosynthesis happens in chloroplast-containing cells. The chloroplast is an organelle that houses the pigment chlorophyll. It is surrounded by a double membrane and houses thylakoids, which look like stacks of coins under an electron microscope. Chlorophyll is contained in the thylakoid membrane. The space between the chloroplast and thylakoid membranes is called the stroma.

Chlorophyll - Cannabis Leaf

Chlorophyll is a pigment that absorbs red and blue light and reflects green light. The green color is what you can see in cannabis leaves. When light hits the thylakoid membrane, the electrons in the chlorophyll become excited. The electrons are shunted to the electron transport chain, which ends up in the production of ATP and NADPH, currencies of energy in living organisms. This step is the light-dependent reaction in photosynthesis. Afterwards, the ATP and NADPH are used for carbon fixation, where the carbon dioxide that enters the stomata is converted to glyceraldehyde-3-phosphate (G3P). G3P is eventually used to produce organic compounds such as glucose and starch. Some sugars are used by the plants for maintenance processes through cellular respiration.

As chlorophyll is made up of carbon, the color of the plants can be an indicator of how much photosynthesis is happening in your plants. Eric Bergeron reminds growers to make sure to keep things green, as this is the color of chlorophyll, the main pigment responsible for photosynthesis.

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“If there is too much water vapor in the air, the water vapor from the stomata is not able to leave. And eventually you’ll start to see droplets or as sedation on the leaf.” 

— Eric Bergeron, Specialist from CANNA

On the other hand, a room that is too dry will stress your plants and force them to close their stomata to preserve water. A visual sign that the air is too dry for your plants is leaf burning or the leaf edges are going upwards. Thus, you need to find a balance between too wet and too dry. 

When choosing cooling and dehumidifying equipment, make sure that it can handle the moisture of a room with massive vegetation pushing a lot of water into the air. The more plants that are in your room, the more water vapor will be in the air.

5. Ventilation

Ventilation Photosynthesis - The fun continues! As Veg room HVAC is complete and now ready for plant’s new home.
The fun continues! As Veg room HVAC is complete and now ready for plant’s new home. – Credit: @torrcann

Another factor that affects transpiration and humidity is ventilation or the airflow in your facility. Grow rooms usually have fans, and the strength of the wind must be controlled so it would not lower the humidity that much. If you have a relative humidity of 60% but the airflow is too strong, the moisture can get dislocated and decrease your humidity down to almost 30%. At this point, the stomata will close, transpiration will stop, and thus so will photosynthesis and the growth of your plant. It can also cause uneven water uptake even though you put the same amount of water for every plant.

6. Vapor Pressure Deficit

Incorporating temperature and humidity, you can calculate the vapor pressure deficit, which gives you a range of values for an optimum environment for growing your plants.

Vapor pressure deficit (VPD) is the difference between the actual air’s water content and its saturation point or the maximum amount of vapor the air can carry at its current temperature. It can be calculated using your relative humidity and temperature values. A warmer temperature will give you a higher VPD value – it means that the air can hold more moisture. In this case, the transpiration rate and photosynthesis will get higher. Nevertheless, a balance between humidity and temperature must be maintained to avoid your plants from getting stressed.

“You get in, it’s warm. You can compensate by increasing humidity. If you get in the room and it’s very dry, you can compensate by having lower temperature.”

– Eric Bergeron, Specialist from CANNA

7. Root Pressure

No matter how much you control temperature and humidity at the upper part of the plant, the water that gets inside will still depend on your roots. Root pressure determines the ability of your plant to pull water in and to push water up. It is affected by three factors: water availability, how freely water can move through the growing medium, and salinity. Water must be available to the roots to absorb, and the physical characteristics of the growing medium can affect this. For example, your plants will have a harder time getting water from coco peat than from Rockwool.

They have some new soil! Products like CANNA COCO, help roots absorb all the essential elements for optimal growing and flowering.
They have some new soil! Products like CANNA COCO, help roots absorb all the essential elements for optimal growing and flowering.
– Credit: @wadeopotatoe603

“Different growing mediums have different capillarity… Different growing media may have a different attachment to water. Not all growing mediums will release water as easily.”

– Eric Bergeron, Specialist from CANNA

Your plant’s ability to push water upwards is mostly dictated by temperature – colder roots push less water up, leading to less nutrient delivery and ultimately, nutrient deficiencies. Many growers do not measure root temperature, so they miss that. Eric advises keeping the temperature in the root zone close to the temperature at the top. 

The last factor is salinity. Sometimes your plants get dehydrated even though water is available in your growing medium. That may be because salinity is too high for the roots to take in water. Roots absorb water through osmosis, which requires that the salt concentration in the medium and inside the roots be equal. When salinity rises a bit too quickly, the plant may not respond that quickly and may lead to dehydration. Your roots will not be able to pull water in. Therefore, the salinity levels of your growing medium must be monitored as well.

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Regular monitoring of these photosynthetic factors is key to the optimum growth to maximize your cannabis plants. As these factors are connected with each other, you cannot take one for granted. The good news is that you can go around these factors by constantly checking and adjusting them for better results. Better photosynthesis, better yield, better income.

Watch Eric Bergeron’s session at the Growers Source Expo by clicking below.

Featured Image Credits: Canva Stock Photos


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