The Best Temperature to Grow Marijuana: Grow Room Temp & Humidity

Growing your cannabis is a rewarding experience.

However, to get this satisfaction, you have to put in a lot of work.

You must adhere to strict guidelines to maintain your plants’ health...and to get maximum yield.

One of these important factors is regulating the temperature.

Whether you’re growing indoors or outdoors, cannabis needs the ideal climate to thrive.

From germination to flowering, these needs will continue to change.

Let’s discuss the best temperature to grow marijuana.

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Why You Need the Best Temperature to Grow Marijuana

All the money that you invest in nutrients for soil and grow lights will be for nothing if your plant can go through photosynthesis.

When temperatures are too low, evaporation won’t occur.

Evaporation is pivotal for the health of cannabis plants.

That’s because the water that seeps out of the leaves during this process creates a stronger suction force between the roots and the plant.

Due to this, transpirational pull happens.

This allows water and nutrients from the roots and soil to reach the areas exposed to sunlight.

Without this process, your leaves will shrink.

Should You Grow Your Marijuana Indoors or Outdoors?

When trying to get the best temperature for marijuana, you want to have as much control as possible.

That’s why temperature-wise, growing indoors is the best.

However, it’s also far more expensive.

You need to create your indoor grow tent to mimic what outdoors life is like.

What Temperature Is Too Cold for Plants Outside?

So, if you live in an environment where temperatures don’t go below 60 Degrees F after dark, then plant it outside.

When you are buying your cannabis seeds, check the label.

If they are bred to thrive outdoors, they should be able to sustain weather as low as 50 Degrees F.

While doable, 50 is not an ideal standard.

The plants will grow much slower when it’s this cold during dark periods.

You’ll also get smaller yields in the long run.

Factors that Affect the Best Temperature for Marijuana

There are so many factors that will go into play when it comes to perfecting the temperature for your grow space.

For one, you need to take into consideration the environment you are living in. 

If you are living in a hot and humid state, your plant is also living in a hot and humid state.

That means there will be more water vapor in the air on top of the evaporation your plants are creating on their own.

How to Monitor the Best Temperature for Marijuana

Excess water lingering in a hot environment can lead to disease and mold growing on your plants.

Therefore, you must monitor the temperature of your grow tent with a thermostat in your room.

Check it multiple times a day and adjust based on how your plants are responding.

What is the Best Temperature to Grow Marijuana Indoors?

The best temperature to grow marijuana indoors will fluctuate between germination to flowering stage.

Throughout the whole process, cannabis enjoys a moderate temperature.

68 Degrees F to 77 Degrees F is the ideal sweet spot to start any grow room.

If you are living in the deserts of Las Vegas, you might want to hover near the 68 level.

Those in the Windy City of Chicago, maybe kickstart your grow tent around the 70’s.

Monitor your plants.

As you get to know them, you’ll figure out the exact best temperature to grow marijuana.

Grow Room Temp and Humidity for Vegetative Stage

Seeing as you will be mimicking the sunrise and sunset outside, with lights on you want to start at your 68 to 77 range.

They need temperatures to be a bit warmer because the energy from the sun needs to penetrate through the soil.

From there, it needs to energize the seeds and promote growth.

If it’s too cold, the sun will spend more time evaporating the water that is semi-frozen in the soil.

Less of a workout is happening for the seeds, leading to a slower harvest and smaller yield.

Grow Tent Temp for Vegetative Stage Dark Periods

Just as you don’t want temps to reach below 50 outdoors, you don’t want it to get too cold with the grow lights off.

You don’t want to maintain the same temp you had during the day.

Your plant needs downtime from all that heat.

With the lights off, have the temps lie between 62 Degrees F and 72 Degrees F.

Whatever you do, don’t have the daytime highs and nighttime lows be too extreme.

This can cause your cannabis plants to go into shock.

Best Temperature for Flowering Stage

As your plant gets older, its needs will change.

One is that it won’t require as much heat.

Therefore, you can start saving a bit on those grow lights.

The best temperature for flowering stage hovers between 65 Degrees F and 85 Degrees F.This all depends on the climate surrounding your grow space.

How to Lower Grow Room Temperature

Being under intense heat all day can end up being costly for your investment.

Therefore, you must act accordingly if you notice the grow room temperature is a bit too high on the thermostat.

To lower the need to keep checking, go for a less intense light source like fluorescent or LED lights.

Check out our guide on fluorescent lights by clicking here.

However, if you do have an HPS light, monitor the temperatures a lot

These lamps can bring on extreme heat levels that reach up to 122 Degrees F.

At, we don’t recommend you use an HPS if you have a small grow room.

Using an Extractor Fan to Control Temperature

One way to draw heat out of your grow room is to use an extractor fan.

They suck in the hot air out of a room, while introducing fresh air into it.

Get an extractor fan based on this equation:

Amount of Watts Divided by 2 = Cubic Meters of Extractor Fan.

If you have one 300-watt HPS lamp, you need a 300 m3 extractor fan.

Three 300-watt HPS lamps, you would need an extractor fan at least 450 m3.

Throw a carbon filter in to keep out bacteria and to keep the scent of marijuana inside your grow area.

How an Extractor Fan Works

If an extractor fan were alone in a room, it wouldn’t have fresh air to suck out.

That’s why they usually need to be attached to a duct.

Hot air ducts attach to your grow lights.

As heat rises, it gets trapped in the duct.

The heat will follow the duct all the way out the window.

By attaching an extractor fan, it helps guide the heat to the duct to make for a more efficient process.

Getting a Portable AC for Grow Tent

An even simpler solution to handle your grow temperature issues is to get a portable air conditioner.

This is ideal for bigger grow rooms because it helps you give extra attention to plants in a certain area of the room that seems to be getting the brunt of the heat damage.

The one downfall of having a portable AC for grow tent is that it leaves the room void of fresh air.

You need to supplement your plants with carbon dioxide to make up for lack of it in the air.  

You’ll still want an exhaust to circulate air too.

Raising the Temperature of Your Grow Room

It’s easier to make a room cooler than hotter.

Naturally, it’s hotter directly under the light.

Therefore, the plants that are in this direct line are getting more nutritional benefits from the light than some of their neighbors.

To spread this heat around, you might want to add an oscillating fan into your grow room.

Face the fan in between the light and plants to shake up stagnant energy.

Make sure to do this in the winter when your living conditions are prone to freezing temperatures.

Your plants not under direct light are more susceptible to these dropping temperatures.

Ways to Raise the Temp in Your Grow Room

If a fan isn’t doing much to move about the heat, or you don’t have enough grow lights, invest in a space heater.

Just make sure to get one with a timer, so you don't leave it running for too long and end up suffocating your plants.

Another option is a radiator with a thermostat.

While these two can do the trick, they’re a bit on the expensive side.

So, only do this if necessary.

Heat Stress on Cannabis Plants

When your plants become too warm, it will put your buds under stress.

Just like humans can’t absorb their nutrients properly under duress, plants can’t perform photosynthesis.

As a result, enzyme activities inside of the plant decreases.

Following the snowball effect, the plants produce fewer proteins.

We’ve been hammered into our heads since childhood that we need protein to grow.

This is especially true for marijuana because this is where the cannabinoids stem from.

Signs of Heat Stress

Heat stress rarely happens in outdoor setups.

However if you live somewhere where the temps reach 105 Degrees F, bring your plants indoors.

You’ll notice signs of heat stress when the top leaves of the plant start to turn inward.

They’ll become a yellow color.

When this happens inside, move the plant away from the grow lights or place the grow lights higher up.

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