Chapter 5

Know Your Temperature + Humidity Goals

As far as your environment goes, there are temperature and humidity goals for you to reach in your grow tent. In VEG & in FLOWER, always try to stay under 80 degrees Fahrenheit, and stay above 60 degrees Fahrenheit. In both VEG & FLOWER, if you stay below 60% humidity, you’ll help yourself avoid one of the most annoying plant diseases, powdery mildew. There are many ways to prevent powdery mildew, but you should start with maintaining humidity between 50% and 60%. In a PERFECT world, you’ll achieve 55% humidity and stay below 75 degrees Fahrenheit. Managing your temperature and humidity in your grow tent is one of your main responsibilities in your home grow. Don’t underestimate their role in your plant’s health.

There is also a “10 degrees rule.” To follow it, simply avoid temperature and humidity fluctuations over 10 degrees. This is because plant’s don’t like it. Use a hygrometer inside your tent to get accurate readings of temperature and humidity. I recommend ordering 2 or 3, this way you can know and verify accuracy. They are pretty inexpensive, but crucial gadgets. Managing the climate inside your grow tent is very important and must be taken seriously.

Keeping your grow tent under 80 degrees Fahrenheit is often challenging to those without air conditioning or for anyone with a strong LED light.

Don’t be fooled, keeping temps below 80 F degrees with a high quality and powerful LED light in your grow tent can be challenging if you don’t have AC or windows to access cool air. Will your plants fall over and die at 854 degrees? No. Ultimately, the main reason to stay below 80 degrees are that terpenes – where the smell comes from – can evaporate in too much heat. Plants may also get stunted with too much heat stress.

When you need to lower the temperature in your grow tent, open the doors of your grow tent. Then, if you can, turn air conditioning on in the room your grow tent is located in. Or you can open windows and blow hot air out or blow fresh cooler air in. If your LED light is dimmable, dim it down until you get below 80 degrees F, as this surely lowers the temperature. You can also add more fans to blow the hot air out of the tent with the tent door open. Or blow cooler air in. If all else fails, just ride it out.

You may see signs of heat stress on your plant. Leaves might “taco”, get burned, crispy, and wilt. Too much heat stress on your developed flowers in FLOWER phase can also cause the terpenes and cannabinoids to degrade, resulting in less potent and less fragrant harvests.

If you ever need to increase the temperature in your grow tent, it’s important that you do NOT put a heater inside of one. Only use heaters safely in a room, NOT inside a grow tent.

If you need to lessen the humidity, you should put a small dehumidifier in your tent. You’ll need to empty it daily if it is collecting water consistently. Or you can run a big humidifier in the room that the grow tent is in. You can also open the windows and try blowing fresh air in or blowing air out.

If you need to increase the humidity, you can mist your grow tent with tap water, or spring water, etc., or you can put a bowl of water with ice cubes and a towel on the floor. You could also boil water in the kitchen if it is in close proximity to your grow tent. You can also try blowing fresh air in from windows, or try blowing air out. Lastly, you can run a small humidifier in your grow tent.

The small dehumidifiers and humidifiers will help to some extent, but don’t expect drastic changes. Usually you’re balancing the use of them with opening/closing windows, running fans, etc. They are helpful if you don’t have central A/C or a portable A/C operating in the room your grow tent is in.


VEG, FLOWER and HARVEST temperature and humidity targets:

VEG humidity: 50 – 60 is your target
VEG temperature: 70 – 80 F is your target; do not get above 80 ideally.

FLOWER humidity: 50 – 60 is your target
FLOWER temperature: 70 – 80 F is your target; do not get above 80 ideally.

HARVEST humidity: 50 – 60 is your target; if it is 70 F – you might need to dry your cannabis for 3 – 4 weeks.
HARVEST temperature: 60 – 70 is your target; do not get above 75 ideally.


Marc Eden’s DIY Cannabis Cultivation Book For Beginners
Published by Green Carpet Growing, Inc.
San Diego, CA 92103
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