What is the best temperature and humidity in the grow room?

Successful cannabis cultivation requires certain tools, tactics and techniques. Knowing the best temperature and humidity in the grow room is a good start.

The ideal temperature and humidity in the grow room depends on the life stage of the plant. Cloning requires a higher temperature and humidity than vegetative growth and flowering plants also have different ideal atmospheric conditions. To master the art of growing marijuana, choosing the right environment at the right time is the most important ingredient for success. So what is the best temperature and humidity in the grow room?

Measurement and change of temperature and humidity

To measure temperature and humidity properly, you need a thermometer and a hygrometer. It is best to invest in a digital device that shows you the current values as well as the highs and lows when you are not in the room. To increase the heat, you need a heater, and to decrease the heat, you need an air conditioner. Depending on the size of the room and how much the temperatures and humidity fluctuate, these devices can be placed outside or inside the grow room. A humidifier and a dehumidifier can be used to raise and lower the humidity. Larger grow rooms can benefit from a controller that uses a sensor to monitor temperatures and humidity and turns on the appropriate device to regulate and maintain them within the set parameters.


a rooted clone of a marijuana plant

Since cannabis cuttings root best in warm conditions with high humidity, the cheap trays with clear plastic domes work remarkably well. In cool conditions, a heating mat should be placed under the trays to maintain an optimal temperature of 23 degree Celsia and a relative humidity of 75-85%. Regardless of where and in what medium you choose to root your clones, warmth and high humidity should be on your priority list. Clones that are too cold or too dry will perish quite quickly. Too high humidity (above 90%) can also lead to mould and rot. Therefore, cut one or two quarter-sized holes 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 phase of growth is 22 degrees Celsia. when the lights are on during the “daytime” and no more than 4 degrees cooler at “night” with a relative humidity of 45-55%. With these settings your plants can best convert the light into energy for growth. This is the time when the plant forms leaves and branches and spreads its root system throughout the growing medium. If it gets too cold or too hot, growth stops and you risk losing your plants altogether.

The flowering stage: Best grow room temperature


The best grow room temperature during the flowering phase is 22 degrees Celsia during the day and no more than 6 degrees cooler at night. If you are supplementing with CO2, temperatures can be 24 degrees or so during the day. During the flowering period you should lower the relative humidity to 35-45% and even to 30% in the last weeks before harvest. This will help you avoid problems with mould, flower rot and mildew that can occur with higher humidity.

Drying and Curing

storaged cannabis - curing phase

The drying room is a place that needs to be carefully monitored. Remember that your plants release a large amount of moisture into the room when drying. It is important to remove the moist air and maintain air circulation in the room without fans blowing directly on the hanging branches, which can dry them out prematurely and cause a harsh taste and burns. Also, growers in dry climates like Colorado have difficulty extending their drying time with humidifiers, while growers in more humid climates like Northern California use dehumidifiers to remove water from the air to prevent mould from forming on their flowers.

The ideal temperature for a drying room is between 20 degrees and humidity between 45 and 55 percent in a dark, well-ventilated room. Cannabinoids, terpenes and flavonoids can evaporate and be released at temperatures above 80 degrees, affecting the scent, flavour and potency of your flowers. Within 6 to 10 days, the branches should break instead of bending and the flowers should feel like popcorn on the outside. This is the right time to cut the individual flowers off the branches and place them in jars to start the ripening process. Let your flowers cure in a cool (20 degrees) and dark place.

The fan is mainly used to set the optimum values, here you can learn about the types of circulation fans for your indoor growing.

Published by Sakul


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