What temp should my grow room be during flowering? 420 Guide for Beginners

Cannabis plants like a temperature similar to humans, or a little warmer — not too dry, not too humid.

For a lot of indoor growers, that is all you need to worry about. If it feels too hot or too cold for you in your grow area, it’s probably too hot or too cold for your cannabis plants as well.

If your grow room feels warm or cold, humid or dry, that is a sign that you may want to look into changing the temperature or humidity of your grow area.

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.

Seedlings

Seedlings and clones respond best to higher humidity levels of 65–75% RH as root systems are not yet well-established. Clones and young plants take in moisture through their leaves.
Room temperature with lights on should be 20–25°C. Lights off, 15–20°C.

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.

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.

Late Flowering

During late flowering, improvements to overall quality can be achieved by keeping temps and humidity as low as possible. Humidity under 40% RH is ideal.

Room temperature with lights on should be 18–24°C. Increase the difference between day/night temps by up to 10°C for even better results.

Basic Hygrometers and Thermometers

The basic tools you need to control the environment in your grow tent or room are a thermometer and hygrometer. You can find good all-in-one digital hygrometer- thermometers for a decent price. If you plan to grow in the years to come, buy the best one you can afford. It will save you a lot of stress and probably some money, too.

ECO FARM Thermo-Hygrometer 2-in-1

• Measure outdoor and indoor temperature, display in Fahrenheit or Celsius, create a comfortable and health condition for you and your family
• Check the maximum or minimum temperature and the humidity
• With back stand and hanging hole at back side
• Ideal household decoration for ensuring you the most desirable ambient temperature and humidity
• Push ‘in-out’ button to select to show inside or outside temperature (in or out will be indicated on LCD screen)

Eco Farm Hydroponic indoor Thermometer Humidity Gauge

Excellent workmanship, stable performance, suitable for sauna room, steam room, strict control of temperature and humidity in sauna room.
This 2-in-1 thermo-hygrometer is the perfect tool for checking the humidity and temperature of the sauna room.
Made of high quality stainless steel, it is durable, wear resistant and high temperature resistant.
The dial scale is fine and clear, easy to read, and is very suitable for sauna room.

Choose the best setup for your grow
Whether you have one plant or ten, design your grow setup ahead of time for the best results. Buy higher capacity or better quality products than you think you’ll need so you won’t have to replace them soon.

Save money by using LED grow lights instead of HID grow lights. It’s a bigger initial investment but you won’t spend as much on electricity and you won’t have to replace bulbs for up to ten years down the road. Plus, you won’t have to cool down your grow tent just because of the lights.

If you’re in doubt as to how much weed is legal in your area, check out this handy site that keeps track of the laws in various states. It’s always better to know before you grow. Then you can plan the appropriate precautions, like a good ventilation system with an odor-reducing carbon filter for indoor grow tent.

Once your plants have matured, use a bud trimmer to make harvesting easier and faster. And don’t toss out those leaves because you can use them to make cannabis oil.