What is the perfect cannabis humidity? Three invisible yet essential environmental parameters exist within the grow room: temperature, relative humidity (RH), and vapor pressure deficit (VPD).
These core, interrelated inputs help foster an environment that supports healthy plant development and, if perfected, can achieve full genetic expression.
Hitting the optimal temperature and RH range throughout the complete grow cycle ensures plants can make the most out of their indoor environment. Yet, throughout cannabis’ lifespan, the ideal RH range shifts. From propagation to vegetative to flower, what RH is best for cannabis?
Grow Room Trifecta: Relative Humidity, Temperature, and Vapor Pressure Deficit
Indoor cannabis cultivators need to manage three aspects of the environment, each playing into one another.
Temperature is the most straightforward: How hot or cold does the room run? Cannabis prefers hotter environments, with slight fluctuations from day to night, mimicking the natural environment.
Relative humidity measures room humidity — how much water the atmosphere holds at any given point.
Together, temperature and RH intersect at VPD. Vapor pressure deficit is the pressure difference between the water vapor currently suspended in the air and the maximum the air can hold at that temperature.
VPD directly impacts cannabis’ transpiration rate, which correlates to photosynthesis. Therefore, dialing in temperature and RH ensures the grow room environment supports full photosynthetic capacity, improved yield, and phytochemical development.
The Ideal Humidity in Propagation
- Temperature Range 65 – 70°F (16 – 21°C)
- Humidity Range (RH) of 50 – 70%
- Target CO2 PPM of 400 PPM
In the beginning stages of growth (cloning, propagation), plants are susceptible to environmental stressors. During this initial stage, reducing the plant’s transpiration rate is important to prevent excess water loss. By reducing leaf water loss, cultivators encourage the plant to photosynthesize to focus on root development.
Once the clones or cuttings have a substantial root system, they can replace any water lost from transpiration. To achieve this, the grow room should maintain 50 to 70 percent RH, and keep the temperature between 65 to 70°F.
The Ideal Cannabis Humidity for Vegetative
- Day Temperature Range 76 – 78°F (24 – 25°C) | Night Temperature Range of 65 – 68°F (18 – 20°C)
- Relative Humidity Set to 60% (Safe Range 50% -75%)
- Target CO2 within 700 – 1,200PPM
Arguably, the vegetative phase is the foundational stage of cannabis production. During this period, the plant focuses on producing its photosynthetic factories— otherwise known as leaves. More vegetative growth translates into higher energy production, laying the groundwork for a productive flower phase.
The grow room temperature should increase during the vegetative phase, with a suggested daytime temperature range between 76 to 78°F and a slightly cooler night range of 65 to 68°F. With RH levels hovering around 60 percent, VPD and transpiration rates increase.
Growers need to achieve higher VPD that allows plants to transpire and cool down without going too far, which could increase the risk of pathogen infestation.
On the other end of the spectrum, if the VPD dips too low, this will impact the plant’s ability to transpire water through its leaves. When this happens, the plant can no longer transport essential minerals, resulting in nutrient deficiency.
The Ideal Cannabis Humidity for Flower
- Day Temperature Range 72 – 85°F (22 – 29°C) | Night Temperature Range 55 – 70°F (12 – 21°C)
- Relative Humidity Set to 50% (Safe Range 45% – 60%)
- Target CO2 within 400 – 1,500PPM
During the final weeks of production, the grow room can hit its highest temperatures and lowest humidity. In the flower phase, the ideal relative humidity drops from veg, down to 50 percent (the safe range is between 45 to 60 percent).
If flowers aren’t bulking up as expected, it may be a nutrient imbalance, but it also may be related to VPD. Low relative humidity during flower can negatively impact cannabinoid and terpene development, leading to a lower-quality final product. If the VPD — the temperature and humidity — isn’t in the ideal range, it will directly impact development.
Uncontrolled RH can lead to serious pathogen spread in the final days of flower. Bud rot and white powdery mildew are just a couple of the risks growers face by pushing the upper limit of RH in the grow room.
Achieve Perfection By Controlling Grow Room RH
The indoor grow room is a finely balanced system; each input feeds into a greater environmental system. Temperature and RH, essential climate parameters, intersect into VPD, which dictates a plant’s ability to transpire and photosynthesis.
Agrify’s Vertical Farming Units make achieving the right balance of temperature and RH possible— even for industrial-scale production. Instead of constantly fighting environmental fluctuations across a large warehouse environment, cultivators create compartmentalized microclimates that are easy to control and can be programmed to strain-specific conditions.
Agrify Solutions enables craft-quality cannabis at scale, with individualized climate monitoring and controls accessible through the Agrify Insights remote dashboard. Agrify promises no more surprises in the grow room, and surefire means to replicate successes.