Climate optimization for cannabis

Added on 21 April 2023

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A healthy, consistent cannabis crop relies on precisely managing temperature and humidity.

Indoor cultivation has several advantages when it comes to cannabis production, but, at a broad level, the No. 1 advantage is the ability to manipulate the environment.

GPN reached out to Brandy Keen, co-founder and senior technical advisor at Surna Cultivation Technologies, to talk about the role climate plays in perfecting the outcome of the harvest. Here, she tackles setting temperature and humidity targets, the role of automation, and prioritizing investments.

GPN: Climate is one of the main reasons to grow indoors, but there’s a lot that goes into creating an ideal climate. Can you talk about the importance of climate management and the impact on the crop?

Brandy Keen: At a high level, the importance of effectively managing the climate for a cultivation facility cannot be overstated. Temperature and humidity affect quality and yields, both as independent variables and in conjunction with each other as it relates to vapor pressure deficit (VPD) and managing transpiration rates. From a general plant health standpoint, excessively high or low temperatures, excessively high or low humidity, inconsistent conditions, and excessively high or low VPD can all cause reductions in yield, negative effects on quality, or complete crop loss. Even if the climate issues seem minor or insignificant, they can weaken the plant’s natural defenses and make them more susceptible to damage from other external stressors such as pests or fungus.

Reductions in transpiration caused by high humidity can lead to mold and rot, and excessively high transpiration can lead to lowered yields, nutrient lock, and unfavorable quality. Excessively high temperatures can cause stretching or hermaphroditism. Excessively low, high, or inconsistent temperature or inconsistent humidity can make the plant more susceptible to powdery mildew, and the list goes on and on.

GPN: What’s the ideal temperature and humidity for a cannabis crop, and what tips do you have for reaching the correct temperature and humidity balance?

Keen: This is a subject of much debate and there are several factors that will influence the “ideal” temperature and humidity. In general, most cultivators target a lights-on temperature for flowering plants of 75 to 84° F and 45 to 65% relative humidity (RH). Lights off is usually 65 to 75° F and 45% to 65% RH. Most cultivators start a little warmer and more humid at the beginning of the flowering cycle and gradually bring temperature and humidity down as the plant matures into late flower. However, these are just rules of thumb and we’ve seen a number of deviations from these ranges — every cultivator will develop his or her own climate recipe. Temperature and humidity are important as isolated variables, but the way they work together to achieve a specific vapor pressure deficit is also important.