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The importance of temperature control in cannabis cultivation

Cultivating your cannabis is a combination of various factors that all need to be in place in order to create a successful crop. We have had a look at light, drying, and a discussion about outdoor growing versus indoor growing. With the help of our man in Johannesburg, Wesley Petzer and Marc Montandon from CarbonActive GmbH, we are now taking a look at the role that heat plays.

The role of heat in cultivating cannabis 

The biggest role that heat plays is something called Vapour Pressure Deficit (VPD). Think of it as the flow that you create if you siphon petrol out of the tank of a car - once the correct pressure has been applied to start the flow, the rest follows automatically. The VPD is achieved by striking the correct balance between heat and humidity. The plant has a negative pressure at the top, so heat pulls the water through the plant to fill this negative pressure. The magic to a successful crop is keeping the balance between heat and humidity correct. The more water flows through the plant, the more nutrients it is being fed.  

“Heat always has a relevance to humidity. When you cultivate cannabis, you have to have a steady and stable environment,“ says Marc Montandon from CarbonActive GmbH, “if you change heat, it changes the humidity and it has an effect on the plant. It can cause the plant to not absorb enough CO2 and this makes the plant not grow properly.” 

Ok, so why is this important? 

Well, it keeps the plants happy. If you are growing outside the sun and the wind naturally removes the vapour that the plant creates. This vapour cannot stay on the plant because it prevents the sucking up of nutrients. When you grow inside, this vapour needs to be removed in order to stimulate the flow. This is what heat does.  

What will happen if I grow a plant and there are huge variables in heat? 

If your plant is too cold, you will not have enough warmth for the evaporation process. In that case your plant will stall. During the vegetative stage you can fix lot of things because the plant is not in flower yet, so in order to address the imbalance, you can extend this period. The flowering period is set, so once that switch is flipped, it’s out of your hands. Things cannot be changed or fixed. This can result in stunted growth, lower yield and other problems that affect the quality of your crop.  

Do you need different heat for different kinds of stages? 

There is no specific temperature for each stage. It is a balance between heat and humidity. You can have high temperature and low humidity, or you can have lower temperature and higher humidity and you will achieve the same result. It is a range of temperatures and environmental factors that need to be sustained. If you live in a place where it’s 40 degrees outside there is no use in cooling your place down to 17 degrees, and vice versa. “Yes, the plant needs different kinds of heat during different stages of the process”, says Marc “and this may be affected by where you are growing. Outdoors you cannot control the humidity and of course light also creates heat, but there is a different heat when you have direct sunlight as opposed to being in the shade. In a cheap greenhouse, you have no way of controlling the heat. You can open it at the top to release some of the heat but if you release the heat, you also release the humidity. In a more expensive greenhouse you can control some of these elements, including airflow. In an indoor facility, and this is why people are willing to spend so much money, that control is absolutely perfect. It is therefore very important for the cultivator to know their plan. When the CBD boom happened in Switzerland, cultivators had to adapt to getting a different result from their plants. The biggest trick is not to change heat too quickly. You can grow at 30 degrees, but then you can’t just drop the temperature to 20 degrees. This causes problems for the plant. If you drop from 30 to 27, that is fine. When people changed from HPS lighting to LED, this was something they had to learn, because the VPD is totally different, and everybody had to raise the temperature 3-5 degrees. In the end you have to find the sweet spot of your plants in the grow room.” 

How green is this artificial creation of heat? 

Well it’s up there with cryptocurrency. Indoor cultivation is so energy intensive that it makes no sense unless your crop is for medical use. This has led to a huge move towards these hybrid greenhouses. In a cultivation cycle you are replacing daylight with artificial light which is a ridiculous amount of power. Facilities need to start looking at solar power and offsets. Remember, there are a lot of opportunities to get your green energy funded. This is why it makes no sense to grow indoor medicinal cannabis in Africa. Energy in Europe is greener – wind, solar, hydro-electric, and it’s cheaper.  

“Yes, we obviously need more energy than growing on a field”, says Marc, “but the business is so small that it does not have a real environmental impact. You can ask the same question about the batteries of Tesla cars. Growing on a field doesn’t always give you the guarantee that there will be food on your plate and that has to be taken into consideration as well. In order to secure the investment, certain sacrifices have to be made. LED lighting was the first step in bringing energy usage down. The system that we use is designed to store the heat. Cooling down a room has never really been that effective, so by extracting heat, we cool the room down in a different way. This heat that has been extracted, then gets stored and it gets re-used when it gets cold in winter.” 

Have you ever paused to consider the additives you use in your cannabis cultivation? Stay tuned for our upcoming article where we explore the impact additives have on the final product