How to Control Humidity in Grow Tent? Step By Step Guide


Are you looking for absolute guidance on how to control humidity in grow tents?

By simply adjusting your grow tent’s ventilation system, lighting system and temperature, you can control the humidity in your grow tent. However, mainly lights are responsible for directly increasing the temperature of your grow tent.

Don’t worry! Garden Synthesis is here to guide you step by step.

Moreover, in this article, we will focus on the following points.

  • How to lower humidity in grow room? Or,
  • How to lower humidity in grow tent?
  • Fundamentals of the grow room temperature and humidity control
  • How to increase humidity in grow tent?
  • How to identify an ideal dehumidifier for grow tent?

But first, you need to know the purpose of building a grow tent. We are sure that you have your own reason, but why are most people using grow tent facilities?

If you are looking for the collection of the best dehumidifier for your grow tent, then checked our linked article.

How to Control Humidity in Grow Tent – Step by Step

Now that you know the main reasons for an increase or decrease in the humidity level in a grow tent, you can easily take the necessary steps by analyzing your grow tent setup.

If you are looking for the collection of the best dehumidifier for your grow tent, then checked our linked article.

Step 1- Adjust The Ventilation and Light System

Ventilation system of a grow tent

The ventilation and lights system in a grow tent is crucial in maintaining you’re grow tent’s temperature and humidity level.

Now that you know how the ventilation system affects the humidity level in a grow tent, you can choose to increase or decrease your humidity level in your grow tent by merely adjusting the airflow in your grow tent.

I have covered an article on how to set up a ventilation system in your grow tent. It should help you adjust your airflow accordingly. This works best if you have an adjustable ventilation fan, but if you have to change your whole ventilation system, hold on to that thought and go through the other solutions first.

Alternatively, you can just cut air holes in your grow tent to increase the airflow and reduce the temperature along with humidity.


Your ventilation system is directly responsible for the temperature in your grow tent as well. So if you want to increase your humidity by decreasing the airflow in your tent, you will also be increasing the temperature.

This can become a significant issue when your plants require high humidity but moderate temperature. Ventilation is not always the solution.

Lights are responsible for directly increasing the temperature of your grow tent. Because of this, they evaporate any surface water in the surroundings adding to the humidity of the grow tent. This air with moisture does not stay in the tent long if you have a sound ventilation system.

When setting up lights, I would advise you to attach a pulley system to the rope ratchets. This will help you adjust your light height because the pulley system should help you to increase or decrease the length of the rope with which your lights are hanging.

To increase temperature and humidity, you can simply lower your lights so that the distance between your plants and the light is not much. You can also adjust your airflow and create a sweet spot for your plants.

Step 2 – Adjusting The Temperature of The Room

By now, you should have a good understanding of how temperature is also related to your grow tent’s humidity level.

So if you decrease the temperature of the room your grow tent is in, you will also be lowering your grow tent’s temperature. This, in turn, will reduce humidity generation, and the humidity level in your atmosphere will also drop.

Depending on your room and local climate, you can open all the windows for a cool breeze to come in and lower the temperature.

You can use the air conditioning or a fan in the room during warm weather if you need to lower the humidity level and temperature.

The solution to this problem is ventilation. If there is good air circulation, your grow tent’s relative humidity will remain the same as the atmosphere where your fresh air is coming from.

Step 3 – Use a Dehumidifier

If you have a proper budget and are looking for a more reliable solution than a hack, I would suggest a dehumidifier.

A dehumidifier is an electrical device that reduces excess humidity in the atmosphere and maintains it to a given level. You can purchase it anywhere for commercial use.

Keep in mind that a dehumidifier reduces humidity and has a tank to collect the accumulated water from your grow tent. Some dehumidifiers come in with a built-in feature where it shuts off automatically when the tank is full.

If you are looking for the collection of the best dehumidifier for your grow tent, then checked our linked article.


Depending on what dehumidifier you use, it can generate heat and make the surrounding region warm.

Step 4 – Reduce plant density

If you are an experienced grower, you will be familiar with the technique of trimming your plants. This gives better shape to your plants and also helps them in various other ways.

If your plants are too bushy, I would advise you to cut off some large and unnecessary leaves. Plants release carbon dioxide when they transpire or breathe. This naturally raises the temperature, which builds up moisture and increases humidity levels in the atmosphere.

When you cut off some of the large leaves, it reduces transpiration, which directly reduces the growing tent’s temperature and humidity level.

Step 5 – Having The Right Soil

As an experienced gardener, you will get to know the various types of soil and their effect. The key is to use soil that is suitable for your plants and also can retain water.

Since they can retain water, they do not add much to the atmospheric moisture, thus controlling the humidity level.

Perlite is really good but very expensive for this case. You can also use sandy soil. These types of soil help retain water and are also suitable for most plants.

If your plants are unsuitable for this kind of soil, cover the top portion of your soil with sand. It will prevent water from evaporating.

The major rule is to avoid any substance or soil that can create dampness. Do not forget to change the soil are appropriate intervals.

Step 6 – Adjust an External Air Conditioning Unit

If budget is not an issue, you can also purchase an air conditioning unit. It is best to buy a portable air conditioner for small size grow tents.

This device, when placed in your grow tent, will pull the heat out of the air. With the heat gone, condensation will take place, which will efficiently remove the air’s moisture.

However, when you are not using the air conditioner, depending on your local temperature, there might be a massive temperature gap that will affect your plants.

Find out the best AC for your grow tent.

Step 7 – Insulate Your Grow Tent

For all these techniques to work, you need to ensure that your grow tent is insulated correctly. Use duct tape as a temporary solution if you find any unwanted or accidental holes in your grow tent.

Why Are Grow Tent Facilities Required?

Grow tent facilities are not mandatory for you. If you are willing to grow plants that are comfortable with warm weather, you may need a grow tent.

However, grow tents are nothing but a frame covered with heat-resistant fabric that can hold the heat inside.

Benefits of Using a Grow Tent

There are tons of benefits of using a growing tent, but we will specify the most important ones here.

  • You can cultivate plants/veggies that are suitable to grow in warm weather.
  • You can grow young plants by controlling the environment.

In a sentence, to get a longer artificial season, you have no way but to embrace the grow tent facilities.

Many gardeners face humidity issues without even realizing it. There can be various reasons for you to choose a grow tent for your plants.

Now you must give them the right amount of light, temperature, and atmospheric humidity.

What is Humidity, and How to Measure It? (Relative Humidity)

Humidity is the amount of water vapour or moisture in the air. Relative humidity (RH) is used to measure water vapour’s percentage in the atmosphere to the total water vapour the air can hold at that particular temperature.

A hygrometer is used to measure humidity in the atmosphere. The reading is in RH or Relative Humidity. You can buy various hygrometers specially designed for commercial use in a grow tent.

A personal recommendation is the Thermopro Digital Monitor. You can easily purchase this on Amazon, and it contains all the necessary readings required to maintain a grow tent and is wireless.

ThermoPro TP50 Digital Hygrometer – Best hygrometer for grow tent

ThermoPro TP50 Digital Hygrometer - Best hygrometer for grow tent

Why You Should Take IT?

  • Well equipped air comfort indicator has been installed.
  • With an efficacy of ±2~3%RH and ±1°F it provides the highest accuracy.
  • You can monitor the highest and the lowest temperature at a glance.
  • Highly weatherproof.

What is The Optimal Humidity Which Is Required for Plants?

During your seeding and early vegging stage, you will need a lot of humidity. 70 to 75% RH is the recommended RH for this phase. If you are cloning, it is advisable to keep it at 70%, but you can still vary by going a little lower up to 75% RH.

During your vegetative stage, you need to lower the humidity. It should be from 40 to 60% RH. This will help your roots to get stronger.

I have always emphasized knowing your plants thoroughly before growing them. You will have to start maintaining the grow tent’s humidity and temperature right from the seeding process.

Each breed of the plant has its required temperature and humidity. However, I have gathered an average that should help you set the optimal humidity for your grow tent at various plant life stages.

As we already said, during your seeding and early vegging stage, you will need a lot of humidity. 70 to 75% RH is the recommended RH for this phase. If you are cloning, it is advisable to keep it at 70%, but you can still vary by going a little lower up to 75% RH.

During your vegetative stage, you need to lower the humidity. It should be from 40 to 60% RH. This will help your roots to get stronger.

The plants must transpire during the flowering stage properly; that is why you should lower the humidity further as the plant grows. Please keep it in 40 to 50% RH. This will ensure proper transpiration, and your roots can absorb water along with other minerals from the soil.

During the final weeks of your flowering, drop the humidity level further to a maximum 45% RH.’

I would advise you to keep the humidity level as low as possible. You will be surprised by the results. However, during the seeding stage, you should keep the humidity high.

What Are The Signs of Humidity Imbalance in a Grow Tent?

Your plants will be showing various signs if you get the humidity wrong. I would advise you to know your plants from the beginning and set the humidity accordingly.

If you set the humidity higher than required, then your plants will start to mould. You will also have mildew issues.


Mildew is fungi that will be easily visible on the surface of plants, usually the leaves. Its colour of white and grey can identify it. Mould is generally green and black. It is the result of a much larger infestation of mildew fungi.

However, if your humidity is too low, then your plants will start to go dry. They will be subjected to heat stress. This will cause your plants to wilt.

Healthy plants can generally recover from heat stress if they are adequately cared for with proper shade and water. However, if your plants are exposed for too long, they will die.

Take immediate action if you start to notice any of the symptoms with your plants. Sometimes it can be too late, but with some quick steps, you might control some damage.

What Happens to The Plants When Humidity is Too High?

Since plants absorb water, it may seem like a good idea to increase the humidity level in the atmosphere of your grow tent. This is a very wrong concept.

Yes, plants need moisture or humidity, but too much moisture will cause various problems in your plants, which will not instantly be visible.

When there is too much humidity in the atmosphere, it becomes a breeding ground for fungi, molds, and various bacteria types. Hence with too much moisture, your plants will become a potential home for various micro-organisms. This will make your plants more prone to diseases and pests.

Plants absorb water through the process of osmosis. Suppose there is too much humidity, then the leaves will start to absorb too much water from the atmosphere. This will cause the roots to stop taking the water from the soil and cause an imbalance in plant growth.

Prolong exposure to increased humidity will result in the roots completely losing their ability to absorb water from the soil. This will also stop the intake of minerals present in the soil. Your plant will become malnourished and may eventually die.

What Are The Causes of High or Low Humidity in a Grow Tent?

There are various reasons why there can be an imbalance in the humidity level in your grow tent.

The most common reason is the lack of proper ventilation. With no appropriate air circulation, the temperature inside the grow tent will gradually rise. This will add more moisture to the air by evaporating the water present in your flower pots’ soil.

In short, a poor ventilation system means increase temperature and humidity in the grow tent. Increased air circulation in the grow tent will reduce the temperature and humidity.

Another reason for increased humidity is overwatering your plants. When you overwater your plants, your soil’s stagnant water starts to get mixed in the atmosphere. This causes a rise in humidity.


For plants that require a lot of water they usually require a hot and moist environment, but if they require less humidity, try to lower your humidity. I will cover them below.

The Led lights in your grow tent produces heat. Since lights are focused directly on the plant, the soil below it receives a certain amount of direct light and heat. This will cause the water in the soil to evaporate and add to the air’s moisture, eventually increasing the relative humidity in your grow tent.

Stagnant water present in your grow tent also adds to your humidity level. Even a little bit of water will add to your humidity, depending on the size of your grow tent.

Another good source of humidity can be your soil. If you have soil that is mostly soggy and damp means that it does not absorb water properly. This will eventually add to the humidity in your grow tent as the soil dries up.

What Are The Effects of Stagnant Water and Overwatering Your Plants?

Stagnant water will eventually evaporate and add to the atmospheric humidity. The same thing will happen if you overwater your plants.

So get rid of any stagnant water in your grow tent if you are looking to drop humidity levels. Alternatively, if you are looking to increase humidity level, soak some sponges in water and leave them in bowls inside your grow tent.

Too much water in your soil pot again will count as stagnant water as this will keep the area soggy and damp. This will raise the humidity level in your grow tent.

It may be necessary to water your plants more than regularly during the flowering stage. However, this may be adding to the humidity level you need to drop during this growth stage.


Have you got the answer, “How to Control Humidity in Grow Tent?”

By now, you must have noticed that temperature and humidity are directly related. The higher the temperature is, the more relative humidity (%RH) the air can hold.

As a gardener, you need to monitor various elements in your grow tent. The humidity level, temperature, airflow, and lights will be interconnected as they affect your plants.

You will need to continually adjust these settings as your plants grow from one stage to another. This will help you get a higher yield.

As a general rule, most plants in high temperature and humidity have difficulty in transpiring. This will affect their nutrient intake and growth.

Before you decide to purchase a dehumidifier and air conditioning, purchase a hygrometer, and understand your grow tent’s environmental factors. Study your plants’ requirements and invest the cash only when you find it difficult to maintain the humidity level after following all the other steps.

Keep experimenting with different setups. Sometimes maintaining a dehumidifier and air conditioning can become much more troublesome than just tweaking your fan speed or adding soaked cloth and sponges in your grow tent.

If you are looking for the collection of the best dehumidifier for your grow tent, then checked our linked article.

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