Indoor cannabis temperature and humidity: Drivers of nutrient delivery
Every grower has their opinion of what is the optimal indoor cannabis temperature and humidity to grow the best yield of cannabis. And this will depend greatly based on the strain and who you ask. The answer to this question changes as often as the temperature outside changes. We do know that it is best to avoid the extreme lows and highs for both.
We are trying to reproduce the perfect outdoor day for growing every day indoors. At times, the grower might change temperature and humidity parameters to stress the plant or to have other effects on the flower produced. Nevertheless, there are a few general rules.
Tips for optimizing indoor cannabis temperature and humidity
It is fairly well known that cannabis grows best somewhere between 70 and 85 degrees Fahrenheit and between 40%-80% relative humidity. This is dependent on the growth stage, strain and growers’ preference. Cannabis can live outside these parameters, but it may not be the best environment to optimize plant growth. And the growth stage of the plant greatly affects the temperature and humidity desired.
Why is indoor cannabis temperature and humidity so important? Many have heard the acronym VPD (vapor pressure deficit), but few understand what it is and why it is important. First, we need to be reminded of how plants feed. Plants need light for photosynthesis as well as for transpiration. Photosynthesis is the conversion of water and carbon dioxide into food using light. The byproduct of photosynthesis is oxygen and water vapor.
Illustration by: Danielle Kobularcik
Understanding Transpiration for Indoor Cannabis Grows
Transpiration is the process plants use to move nutrients throughout their tissue and then release this moisture through their stomata to the surrounding air. The water moves hydraulically from the roots at a higher pressure through the plant and out the stomata to the atmosphere, which is at a lower pressure (optimally). If the surrounding air is not at a lower pressure, then water and nutrients will not effectively move through the plant hydraulically.
VPD is the difference between vapor pressure at the surface of the plant leaf vs the vapor pressure in the air. Air Temperature, humidity and leaf temperature are the variables that determine vapor pressure deficit. VPD is usually read in Kilopascals (Kpa).
If the VPD is too high the plant will transpire too much and if it is too low, it will not transpire enough. There are different target VPDs depending on what growth stage the plant is in. For example, Vegetative cannabis plants usually optimize their transpiration at a VPD of 0.9 to 1.1 Kpa and Flower between 1.1 & 1.5 Kpa.
VPD Chart By: Pulse Labs, Inc.
Once the water vapor has been released into the air by the plant, it is the HVACD systems job to remove all the vapor except what is left behind to maintain the desired humidity level and VPD. At the same time the HVACD system also needs to condition the space to maintain the proper air temperature.
Therefore, indoor cannabis temperature and humidity are important. If the proper temperature and humidity is not maintained, the plant will not receive proper amounts of nutrients. Without correct VPD the plant will not be optimally fed. Therefore, indoor cannabis temperature and humidity are the vehicles that drive transpiration to deliver nutrients throughout the plant.
Why Partner With Anvil Agrinomics
Anvil Agrinomics, LLC (AnvilAg) is a leading MEP (Mechanical, Electrical, and Plumbing) engineering design firm centrally located in the United States. While we serve a diverse range of industries, our specialty lies in designing controlled environments for indoor agriculture and facilities dedicated to the manufacturing of infused products. Our expertise helps businesses optimize their operations and achieve regulatory compliance while creating efficient and sustainable environments.
About the Author: Jim Megerson, PE, LEED AP
With a career dedicated to engineering excellence, Jim Megerson’s work at Anvil Agrinomics has culminated in the successful delivery of nearly 40 projects across 15 states, encompassing about 1 million sqft of cannabis cultivation and manufacturing spaces. His team's expertise in creating cost-effective solutions has been pivotal in supporting customers to thrive in the emerging markets of medical and recreational cannabis, as well as future organic indoor agricultural farming. The goal is always to optimize plant propagation through precision in temperature and moisture control.
Passionate about sustainability, he applies creativity and innovation to every project, aiming to minimize the impact of built spaces on the natural environment. His commitment to sustainable design and operations reflects in the work he does, ensuring functional spaces that are conducive to not just living and working, but also to the growth and health of plant life.
