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What’s the Best Grow Room Temperature and Humidity Level?

Successfully growing cannabis requires specific tools, tactics, and techniques. Knowing the best grow room temperature is a good start.

best grow room temperature
Garden temperature is a critical factor in photosynthesis and plant development.

Ideal grow room temperature and humidity varies depending on the stage of plant life. Cloning requires higher temperature and humidity than vegetative growth and flowering plants have different ideal atmospheric conditions as well. In order to master the art of marijuana growing, dialing in the proper environment at the right time remains the most essential ingredient for success. So, what is the best grow room temperature and humidity level?

Measuring and Changing Temperature and Humidity

In order to properly measure temperature and humidity, you’ll need a thermometer and hygrometer. Best to invest in a digital one that can give you current readouts as well as highs and lows when you’re not inside the room. To raise heat, you’ll need a heater and to lower heat, you’ll need an air conditioner. These can be outside or inside the growing space depending on the size of your space and how much the temps and moisture levels fluctuate. A humidifier and a dehumidifier can be employed to raise and lower humidity rates. Larger grow rooms can benefit from a controller that uses a sensor to keep track of temps and humidity and turns on the appropriate appliance to regulate and keep them within your set parameters.

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.

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The Flowering Stage: Best Grow Room Temperature

The best grow room temperature during the flowering stage of growth is 68-75 degrees during the day and no more than 10-15 degrees cooler at night. If you’re supplementing with CO2, daytime temps can be as high as 75-82 or so. During flowering, you should lower your relative humidity to 35-45% and even lower (30%) for the last couple of weeks before harvest. This will help you avoid issues with mold, bud rot and PM (Powdery Mildew) that can arise in higher humidity.

Drying and Curing

The drying room is a place that must be carefully monitored. Keep in mind that your plants will be giving off a large amount of moisture into the room as they dry. It’s important to pull wet air out and keep air circulating in the room without actually having fans blowing right on your hanging branches, which can dry them out prematurely resulting in a harsh taste and burn. Also, growers in dry places such as Colorado struggle to extend their drying time with humidifiers, while farmers in more humid climates such as Northern California use dehumidifiers to pull water from the air in order to avoid mold growing on their buds.

The ideal temperature for a drying room is between 65 – 74 degrees Fahrenheit and humidity between 45 – 55 percent in a dark well-ventilated room. Cannabinoids, terpenes, and flavonoids can evaporate and be released at temperatures above 80 degrees, diminishing the scent, flavor and potency of your buds. Within 6 – 10 days your branches should snap instead of bending and the buds should feel popcorn dry on the outside. This is the time to cut the individual buds from the branches and put them into glass jars to begin the curing process. Cure your buds in a cool (68-72 degree F.) and dark place.

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Written By

Danny Danko is a writer, photographer and the Senior Cultivation Editor of High Times magazine. He has selected High Times’ annual Top 10 Strains of the Year since 2005 and is also the creator and founder of the High Times Seed Bank Hall of Fame, author of The Official High Times Field Guide to Marijuana Strains and the forthcoming book Cannabis: A Beginner's Guide to Growing Marijuana. He hosts the podcast High Times presents "Free Weed from Danny Danko."

6 Comments

6 Comments

  1. Avatar

    Melissa V Valdez

    March 9, 2020 at 3:37 pm

    I’m assuming this is for soil

  2. Avatar

    Gaines Love

    March 31, 2020 at 12:43 am

    All u p0t heads didn’t have a clue about mareawanna , I didn’t either but growing up NLR, Ar.where I40 runs east of Protho Junction. My Uncle Charlie Been had a 8 acre farm back in the day and his cows got sick on what was called loco weed what is now called marawana . U w0nder why your loco ? Think about it…

    • Avatar

      Adrian Stoner

      April 9, 2020 at 6:59 pm

      this response makes me laugh
      poor sick cows.. lots of other plants far worse haha!!

      Good story!

      • Avatar

        Joseph Guglielmo

        August 9, 2020 at 1:02 am

        That’s so true..lol

    • Avatar

      Phytoplankton

      April 11, 2020 at 1:03 pm

      Loco weed is from the genus Datura (Nightshade family), i.e., Jimson Weed, and is not related to Cannabis. Jimson weed and related Datura’s are commonly found in pasture lands.

  3. Avatar

    Lee

    August 7, 2020 at 1:48 pm

    Looking for help on finding out how to make real polin ??? Pls help can any body point me in the rite direction..all the sites are so different need proper advise

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