Ideal Temperature and Humidity for Grow Tents

Are you an indoor cannabis cultivator? Do you sometimes get less than expected yields, or worse, lose your entire crop to mold? You may not know the ideal temp and humidity for your grow tent. 

Growers of any skill can cultivate average marijuana. The plant manages just fine when left to its own devices and even produces a few colas. If you’re after more than just mediocre, your crops need to live in a closely regulated environment. 

Keep reading to discover the ideal temp and humidity for your grow tent, and ensure you always maximize your harvests. 

Why keeping grow room temp and humidity at ideal levels is so important

Grow tents offer a level of control that’s simply impossible to achieve outside.

The basics of indoor growing are quite well-known. Keep your plants in an enclosed and ventilated space and use lights to simulate sunshine.

An overlooked fact is how crucial it is to monitor the temperature and humidity inside the space. Should these parameters go unchecked, they may result in issues like mold, mildew, and rotting buds.

Cannabis needs different things from its environment as it develops and enters new life stages. When beginning its next phase, the temperature for growing weed and humidity levels surrounding it must also change.

Giving your plant the best habitat possible means that you won’t have to stress about the quality of the buds you’re growing. 

Ideal temp and humidity for grow tent by stage

Let’s look at each life stage of a marijuana plant, and the grow room temp and humidity level it needs.

Grow room temp and humidity chart

The environment inside your tent during each of the plant’s growth phases should be as follows:

Seedling stage

While cannabis seeds are germinating, being kept in warm and humid conditions encourages them to sprout. 

Maintaining a temperature of between 75–85℉ and a high humidity level of 65–70% is critical for their development. 

Air holding increased water vapor allows the seedlings to draw in H₂O through their leaves. This process gives the immature roots enough time to grow.

Cultivating seedlings at the temp and humidity level the plants prefer ensures their survival.

Vegetative stage

Marijuana’s roots are more developed at the vegetative stage and can take up all of the liquid the plant needs. Now’s when you’ll see your seedlings go through a massive growth spurt. 

When your crops enter this phase, the temperature in the tent can remain the same. To keep your development on track, begin to provide drier surroundings.

It’s best to make this change gradually. Lower the amount of water vapor in the air by 5% a week until you reach the optimal range of 40–60%.

The veg temp and humidity levels keep the young foliage healthy and prevent it from becoming too wet. 

Saturated leaves can’t release enough oxygen, impacting how much light they absorb. 

When plants don’t receive enough rays, they can’t take in all the nutrients they need. Unhealthy shoots adversely affect your cola production and decrease your yield. To protect your harvest, controlling cannabis humidity is vital.

Flowering stage

As cannabis begins to bloom, it becomes more temperamental. It only flourishes in cool, dry air.

The best temperature and humidity for the flowering stage are ones kept low. Try to regulate an environment of 65–75℉ and 40–50% water vapor. 

Avoid heat at all costs, as it makes the air damp. This mugginess decreases evaporation from the foliage, resulting in a continuous layer of moisture on the buds. Plants that remain wet for too long begin to rot, which is disastrous for your crops.   

Late Flowering Stage

Altering the conditions surrounding your marijuana at this stage is not strictly necessary. It’ll continue to grow and bloom in the same surroundings.

If you’d like to improve the appearance and flavor of your buds, put extra effort into your cannabis temp and humidity. 

Now’s the time to lower that water vapor level to around 30–40%. 

The difference between day and nighttime temperatures should be at least 5℉. The safest way to achieve this is to cool down your grow tent during the evenings.  

The thermal contrast sends a message to the plant to release more growth hormones that trigger bud development. Expect more blooms with increased density and a spectacular taste and smell.

Never expose your cannabis to high temperatures at this phase. You may accidentally burn away some of your precious terpenes and cannabinoids, ruining your harvest quality.

4 tools to monitor and control the temp and humidity for weed

Maintaining the best temp and humidity for your weed is vital for a successful marijuana harvest. It’ll be easy to control what’s happening in your grow tent if you have the correct equipment.

Here are four essential tools you need to ensure that the conditions in your cultivation space are always optimal.

Thermometer

It’s not feasible to grow cannabis indoors without a good quality digital thermometer. Any well-organized grower has two available to ensure that the correct temp and humidity for weed are in place.

Hang a wall-mounted version in an area that’s easy to see upon entering. It’ll only display the conditions of its immediate surroundings, so get a second, portable tool, too. 

Use this thermometer to get readings at different spots in the room, especially up close to the plants. This information ensures that your crops are in the best locations and is a good form of cannabis heat stress prevention.

A transportable device is also excellent for verifying that the temperature shown on equipment such as ACs or thermostats is accurate.

Hygrometer

This is an indispensable tool for achieving the most effective temp and humidity for cannabis growth. 

Hygrometers measure how much water vapor is in the air. You should also own both wall-mounted and portable versions of the device for multiple readings.

It’s crucial to invest in a good-quality tool to ensure you see accurate measurements. 

Staying up-to-date about the humidity in your grow tent allows you to intervene in time should something go awry. There’s nothing worse for a cultivator than losing an entire harvest to rot or mildew. Be sure to maintain an ideal temp and humidity in your grow tent.

AC

It’s a common misconception that fans lower the temperature inside a room. They move air around and are important in grow tent ventilation but useless at reducing warmth.

Meticulous climate regulation is vital for growing top-quality cannabis, and ACs are a reliable way to control your cultivation space. Both wall-mounted and portable models effectively maintain the ideal temp and humidity for weed.

Being easily programmable, they adjust tent conditions according to the life stage of your crops. The fan inside the unit also circulates air.

Humidifier/Dehumidifier

Many methods can modify the amount of water vapor hovering around your cannabis plants. Mist marijuana with a spray bottle to increase humidity. Only water seedlings when the lights are off to decrease it.

While techniques like these do work, they’re far from precise. 

If you want to achieve a massive harvest from your seeds, invest in a humidifier or dehumidifier. It’s a much more consistent way to reach the exact percentages you need. Just make sure you get one with an adequate tank size for your tent.

Frequently asked questions about temp and humidity

Is 60 humidity too high for flowering?

Yes, it’ll be game over for your plants.

While in the flowering stage, the temperature and humidity for cannabis must be kept low. A level of 60% inside your tent means plants can’t transpire properly and are constantly moist, which results in rot.

Rather invest in a dehumidifier that can keep the level around 50% and save your seeds.  

Will mold grow at 55 humidity?

Nope, your plants should be ok.

At a humidity of 55%, water can effectively evaporate from the leaves, keeping them dry. Mold usually only grows in damp conditions. 

Decreased ventilation may also bring on mildew. Make sure that there’s enough airflow in your tent, and you’ll be good to grow.

Remember to also use an ideal temp and humidity in your grow tent.

Can a fan lower humidity?

It depends on how you’re using it.

If your fan is blowing in an enclosed space, it’s just moving the same air around. It does nothing to decrease the amount of water vapor present.

Using your machine to ventilate your grow space could lower the humidity if you’ve put it in the best possible position.

When a fan is near an outside source of cooler air, a fresh breeze will flow into the room. It’ll circulate and eliminate some of the water vapor floating around. 

Correctly positioning your equipment is key in maintaining the ideal temp and humidity for your grow tent.

Refine your growing by using the best temp and humidity for your weed

Any average Joe can easily grow ordinary cannabis plants. 

Cultivating superb specimens bursting in flavor and smell requires more refined techniques.

Environmental conditions have the greatest influence on how well plants grow. Investing in expensive lights and nutrients is pointless if you’re not keeping your plants’ habitat under control. 

Go the extra mile and ensure your grow room temp and humidity are at the optimal level for cannabis growth.

Taking daily measurements and making adjustments may seem tedious, but it pays off come harvest time. Your precious seeds will be safe from rot and other diseases. They’re also guaranteed to give you a bumper harvest of dense, aromatic buds.

Keep our grow room temp and humidity chart on hand to ensure that you always give your plants the conditions they need to flourish.

We hope you’ve found this article helpful in your quest to produce high-quality cannabis. If you’re looking for seeds to cultivate in your grow tent, check out the Homegrown Cannabis Co store.

About the Author: Kyle Kushman

Kyle Kushman is a legend in the cannabis community. He is the modern-day polymath of pot: cultivator, breeder, activist, writer, and educator. After winning no less than 13 Cannabis Cups, there’s nothing this guy doesn’t know about indoor growing - he’s been there, done it, and is still doing it to this day!