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The Right Temperature In A Marijuana Grow Room

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Having the right temperature in your grow room is vital for your plant to photosynthesize. If the temperature is too low, it will lessen the evaporation through the leaves and cause the suction force to shrink, which affect how nutrients are consumed by the roots.

Required nutrients will haven’t been consumed will stay in the growing medium and over time dissolve in the root system. A growing medium that is highly acidic lessens the effort the roots put in which leads to the plant taking in less water and nutrients, and it may stunt the growth.

Even though it may have started off as something that did not seem like a big deal, it could become a major problem in another area of the plant. With that being said, it is necessary to have the right temperatures in your growing space. So, let’s go into more detail about the best temperature and how to properly control the environment.

In this article we will cover:

The right temperature
Measuring the temperature
How to lower the temperature
Raising the temperature

The right temperature

The right temperature in your marijuana grow room

There are many things that determine the temperature in your grow room. Where you grow room is situated in the home is critical. For instance, it is much cooler in the basement than it is in the attic. Also, room size, air flow, how many lights you have and the extraction amount all have something to do with it. You will need to consider this when creating a grow room.

Download my free marijuana grow guide and learn to grow like a pro!

When the light is on, the best temperature for seedlings and cuttings is from 68*F to 77*F. Once your plants mature, they can handle even more and the temperature could rise to as much as 82*F. If the light is off, the temperature needs to be around 62*F to 72*F. One other critical point is that the temperature changes between day and night and can never be too high. When the temperature is 82*F in the daytime, it should never be below 64*F at night.

Measuring the temperature

Measuring the temperature in your grow room

The temperature in your room should be measured with a thermometer. You can find both digital and analog thermometers in several locations for only a few dollars. I usually prefer a digital thermos/hygrometer such as this one, which has a built-in memory, so I am able to see what the maximum and minimum temperature was. I suggest a thermometer that has a temperature sensor on a wire, that way you can hang the display outside of the grow room so you can monitor the temperature when the lights are off.

Remember only to measure the temperature in a shaded area and different parts of the grow room. Put a few fans in the room for good air flow. Lamps will not change the air temperature, but it will usually be a little warmer under the lamp than it is in the shaded areas. This is nothing to worry about, just be sure there is enough space between the lamp and the plant. You do not want the tips of the plant to get burned. The lamp heat will influence the room temperature.

How to lower the temperature 

How to lower the temperature in your grow room

Too much heat can easily become an issue in the grow room. The lamps used to grow create so much heat! With fluorescent lights, it is not so much of an issue. However, HPS lamps may raise the temperature to extreme levels of 122*F, which could kill your plants. You have to understand the range of the grow room. With 600-watt HPS lamps, use a space no less than 3.2 ft. x 3.2 ft. x 6.5 ft. every time.

Download my free marijuana grow guide and learn to grow like a pro!

To extract heat, use this easy method; the amount of watts divided by two = extractor in cubic meters (feet). So, 2 x 600 watt HPS needs an extractor fan of 600 m3. Extractor fans blow the hot air out of an area and bring in fresh air. You can even add a carbon filter to ensure the marijuana smell doesn’t go out of your room. Using ballasts placed outside of your grow room also creates plenty of heat, so check for that too.

The simplest way to make sure the temperature remains low is to keep them on at night. The lamps will come on for a few hours once the sun sets and go off a couple of hours after the sun comes up. Doing it this way keeps the lights on during the cooler parts of the day. Some experienced growers use an air conditioning unit in order to run it throughout the day and night.

Raising the temperature

Raising the temperature in your grow room

You do not have to raise the temperature if the lights are on. The lamps will do that on their own. It is critical that the air is moved throughout the grow room equally so that you have the same temperature all over. You can get swivel fans for this purpose and face them between the lamps and the plant. Any fresh air from outside need to be moved throughout the space so there are no cold spots. This is definitely the case in the winter when the temperatures fall below freezing.

It can become cold in the room when the lights are off. To raise the temperature use a space heater with thermostat to heat up your grow room. Just keep in mind that they use a lot of electricity. Also, radiators with thermostats are good as well. You can even turn off the extractor fan when the lights turn off. You can do this with a fan controller that has a thermostat, or a timer.

Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible.