Cannabis BasicsGrow Room Enviroment

Cannabis Grow Guide Air Temperature and Humidity

The Environment

Cannabis Grow Guide Air Temperature and Humidity, Air, temperature and humidity are closely linked and all are important factors in providing a good environment for your plants. Outdoor growers are at the mercy of the elements so control of the environment is limited for them, for indoor growers however things are different. Luckily the environment in your average heated house is close to the ideal conditions for cannabis growth. This makes indoor growing the best option in cooler climates like the UK.


Cannabis Grow Guide Air Temperature and Humidity
Cannabis Grow Guide Air Temperature and Humidity

Grow room ventilation

Grow room ventilation, Unlike us plants can`t move to get fresh air. When kept inside or in a greenhouse they can suffocate if the air around their leaves is not changed. During the night when plants are working on their roots and not producing any of their own oxygen the need for fresh air is even more important. To get the best from your plants therefore use circulating fans and ventilate or use extraction fans day and night.

cannabis temperature and humidity chart
cannabis temperature and humidity chart

CO 2

Cannabis plants need to be able to extract Carbon dioxide (CO 2) from the air to use as a building material. The amount of CO 2 a plant can use depends directly on the amount of light it receives. Low light gardens (around 1000 lumens per sq. ft) will not be able to use any more CO 2 than is available naturally in the air. Higher light gardens can use more CO 2 but only if it is delivered in the right place, at the right time, at the right temperature and in the right amounts. Unless you have no fresh air ventilation at all or are a commercial grower CO 2 injection can be a lot of hassle and expense. It`s easier just to constantly pump in fresh CO 2 laden air.

Oxygen For Roots

For healthy growth you need to make sure a plants roots have direct access to oxygen on a regular basis. In pots this means allowing the medium to dry out a bit between waterings. In hydroponics it means making sure you don`t saturate your medium too much. Flood and drain only once or twice a day or use NFT systems where most of the roots are out of the medium anyway. Healthy roots are bright white while roots starved of oxygen will start to go brown.


Talking to plants

Some growers believe simply being with your plants is an easy way to improve their air. Humans breathe out CO 2 all the time so plants really do benefit from being around people. Sound vibrations from talking or music will also strengthen a plants stems. Keep it to yourself but talking and playing music to your plants will help them grow bigger and stronger.



Cannabis can survive in temperatures ranging from freezing to 100 degrees but such extremes will slow growth and lower potency. For the best results during a plants day time keep temperatures between 70 and 85 degrees. At night aim for between 50 and 70 degrees. If heat becomes a problem try timing the light cycle to come on at cooler times like during the night. Using a thermometer with a min max setting will also make sure you are aware of temperature fluctuations that take place when you are not around.


Extra Heating Indoors

Adding more HID lights is a good way to increase the temperature in a grow room. They kick out nearly as much warmth as a heater of similar wattage but also have the advantage of extra light. If your heat problems are during the plants night time use a standard heater instead but make sure any ‘on’ light is covered to stop it interrupting or interfering with the plants dark cycle. Simply raising plants off the ground on a table or pallets allowing a ‘sink’ for cold air will also help.


Extra Heating Outdoors

Water in a good storer of heat so areas around large expanses of water are always a few degree`s warmer than inland areas. You can mimic this by placing water storage barrels near outdoor plots. Paint them matt black and they will warm up during the day and release their stored heat during the night, all for free.



The humidity is the amount of moisture in the air, the warmer the air the more moisture it can hold. In a hot grow room even of a modest size plants could be chucking litres of water into the air every day. This water laden air won`t effect growth directly but it needs to be extracted or vented out to avoid problems with moulds and fungus. Ventilate outside if possible as the moist air will condense on cooler inside walls causing damp like problems. Aim to keep humidity levels between 40 and 60% all the time as lower levels will also invite problems. These range from dry air loving pests like spider mites to a slowing down in CO 2 and light uptake if the atmosphere gets really dry.


Help Leaves Breathe

Cannabis plants use the underside of their leaves to breathe. Fans blowing up from underneath plants will help them maintain adequate levels of CO 2 where they need it. They will also also help to keep down the humidity levels under the canopy.

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