How much humidity should be in a grow room? 2020 Updated
HUMIDITY LEVELS AND TEMPERATURES: FROM SEEDLING TO HARVEST
We need to define what humidity and temperature control actually means when growing cannabis. It makes sense to divide the life of cannabis plants into 4 different stages in which humidity levels, and temperatures, should be adjusted to ensure healthy growth. Don’t think that humidity and temperature control is complicated and not worth it! It’s generally very easy, and more about keeping parameters within a certain range, and as constant as possible.
The first thing you need to do is to buy a hygrometer and thermometer, preferably a digital one with memory function, also showing maximum and minimum values of the past. Some hygrometers aren't the most accurate, so don’t bother having several devices in your grow tent for weeds to compare values. Now that we’re able to closely monitor our conditions, we can get to the essence of humidity and temperature control – the actual humidity levels and temperatures we aim for.
Cloning
Because cannabis cuttings root best in warm conditions with high humidity, the cheap trays with clear plastic domes work remarkably well. In cool conditions, a heat mat should be placed underneath the trays to maintain an optimum temperature of 74-78 degrees F. and relative humidity at 75-85%. No matter where and into what medium you plan to root your clones, keep warmth and high humidity on your priority list. Clones allowed to get cold or dry will perish quite quickly. Too much humidity (over 90%) can also cause mold and rot, so cut a quarter-sized hole or two in your clear plastic dome to allow some air movement and circulation.
The Vegetative Stage: Best Grow Room Temperature
The best grow room temperature during the vegetative stage of growth is 70-78 degrees F. when the lights are on during the “daytime” and no more than 10-15 degrees cooler at “night” with a relative humidity of 45-55%. With these settings, your plants will best be able to convert light into energy for growth. This is the time when the plant puts on leaves and branches and expands it’s root system throughout your growing medium. If it gets too cold or hot, growth stops and you eventually risk losing your plants altogether.
At the early flowering stage, most growers agree that plants benefit from lower humidity levels. Again, there’s no ideal figure to aim for, but many will stick between 40–50%, occasionally pushing to roughly 55%. You’ll also want to drop temperatures to about 20–26°C (68–78°F).
During the late flowering stage, try to drop humidity to about 30–40% and keep temperatures around 18–24°C (64–75°F) during the day, followed by slightly cooler nights (16-20C in the last few nights).
How do you measure the humidity?
You can measure the humidity with a hygrometer. Hang the hygrometer just above the plants, in a well-ventilated area. This way you can also monitor the humidity when all the lights are off in your grow room. Often they also come with a memory that keeps track of the highest and lowest values, so you can see if you stayed within the margins.
Grow Room Humidity Control: Tips for Indoor Growers
Control Your Temperature
Temperature is a concern for every grower, given the immense amount of heat that grow lights for indoor plants can produce. But, when controlling temperature, consistency is key.
Air Movement Is a Must
Despite the fact that it holds water, humid air is lighter than the rest of the air surrounding it, so it rises to the top of a grow room. CO2, critical for plant growth, settles near the bottom of the room.
Use a Dehumidifier for Plants (and Size It Properly)
It may sound obvious to use a dedicated dehumidifier when trying to control humidity, but in all his years of experience, Howard says it’s an area where he has seen many growers—particularly new ones—try to cut corners.
We need to define what humidity and temperature control actually means when growing cannabis. It makes sense to divide the life of cannabis plants into 4 different stages in which humidity levels, and temperatures, should be adjusted to ensure healthy growth. Don’t think that humidity and temperature control is complicated and not worth it! It’s generally very easy, and more about keeping parameters within a certain range, and as constant as possible.
The first thing you need to do is to buy a hygrometer and thermometer, preferably a digital one with memory function, also showing maximum and minimum values of the past. Some hygrometers aren't the most accurate, so don’t bother having several devices in your grow tent for weeds to compare values. Now that we’re able to closely monitor our conditions, we can get to the essence of humidity and temperature control – the actual humidity levels and temperatures we aim for.
Cloning
Because cannabis cuttings root best in warm conditions with high humidity, the cheap trays with clear plastic domes work remarkably well. In cool conditions, a heat mat should be placed underneath the trays to maintain an optimum temperature of 74-78 degrees F. and relative humidity at 75-85%. No matter where and into what medium you plan to root your clones, keep warmth and high humidity on your priority list. Clones allowed to get cold or dry will perish quite quickly. Too much humidity (over 90%) can also cause mold and rot, so cut a quarter-sized hole or two in your clear plastic dome to allow some air movement and circulation.
The Vegetative Stage: Best Grow Room Temperature
The best grow room temperature during the vegetative stage of growth is 70-78 degrees F. when the lights are on during the “daytime” and no more than 10-15 degrees cooler at “night” with a relative humidity of 45-55%. With these settings, your plants will best be able to convert light into energy for growth. This is the time when the plant puts on leaves and branches and expands it’s root system throughout your growing medium. If it gets too cold or hot, growth stops and you eventually risk losing your plants altogether.
At the early flowering stage, most growers agree that plants benefit from lower humidity levels. Again, there’s no ideal figure to aim for, but many will stick between 40–50%, occasionally pushing to roughly 55%. You’ll also want to drop temperatures to about 20–26°C (68–78°F).
During the late flowering stage, try to drop humidity to about 30–40% and keep temperatures around 18–24°C (64–75°F) during the day, followed by slightly cooler nights (16-20C in the last few nights).
How do you measure the humidity?
You can measure the humidity with a hygrometer. Hang the hygrometer just above the plants, in a well-ventilated area. This way you can also monitor the humidity when all the lights are off in your grow room. Often they also come with a memory that keeps track of the highest and lowest values, so you can see if you stayed within the margins.
Grow Room Humidity Control: Tips for Indoor Growers
Control Your Temperature
Temperature is a concern for every grower, given the immense amount of heat that grow lights for indoor plants can produce. But, when controlling temperature, consistency is key.
Air Movement Is a Must
Despite the fact that it holds water, humid air is lighter than the rest of the air surrounding it, so it rises to the top of a grow room. CO2, critical for plant growth, settles near the bottom of the room.
Use a Dehumidifier for Plants (and Size It Properly)
It may sound obvious to use a dedicated dehumidifier when trying to control humidity, but in all his years of experience, Howard says it’s an area where he has seen many growers—particularly new ones—try to cut corners.
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