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.
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.
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
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.
Garden temperature is a critical factor in photosynthesis and plant development.
The Flowering Stage: Best Grow Room Temperature
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?
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.
Generally, cannabis plants prefer temperatures in the 70-85 °F (20-30 °C) range during the day when lights are on. When grow lights are off (their “night”), cannabis plants are happy with slightly cooler temps.
7 Essential Concepts About Temperature Control
Cannabis plants like about the same temperature as humans!
Temperature & Humidity Adjustment Cheat Sheet
Please note temps above 80°F (26°C) in the flowering stage will slow down bud growth and may cause them to become airy and loose. The heat can also reduce the potency and smell of your buds. Keeping the grow room temperature under control is especially important in the flowering/budding stage!