How to Lower Humidity in Grow Tent or Grow Room

As indoor growers, keeping the relative humidity in check can sometimes be risky and cause problems.

Experienced indoor growers know that the optimal humidity level in your grow tent is critical to successfully growing indoor plants. If the humidity is too high in your grow tent it is how to lower humidity in grow tent.

High levels of humidity can lead to slow growth, bud rot, fungal growth, mildew, and mold. Such factors threaten the survival of your plants, including your chances of high yields.

Your grow tent shouldn’t exceed 70% humidity. So, if you’re surpassing that level, you have to determine where the moisture is coming from, and what can be done to stop it from harming your plants.

Worry not, maintaining an ideally low humidity level in your grow tent could be solved by the very things found in your grow tent, so here how to lower humidity in grow room without having to shell out lots of money!

Understanding Relative Humidity

Let’s begin with a short science lesson: humidity is the water vapor found in the air.

Meanwhile, relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity.

In simpler terms, relative humidity is the air that is completely saturated with water vapor and cannot hold it any longer.

Remember that water vapor will always be in the air. The air will hold more water vapor when the temperature in your grow tent is higher.

Heat causes the water to move faster through the air, resulting in higher humidity.

Why High Humidity Is Bad And Causes Problems

Why High Humidity Is Bad And Causes Problems

So, you’ve been told that high humidity is imperative to ensure robust growth and health of your growing plants.

In fact, plants love high humidity. While this is true, excessively high levels of humidity in your grow tent can lead to more harm than good.

If you DO NOT want your grow tent to:

  • Become the perfect environment for bacteria and molds;
  • Make your flowering plants suffer from bud rot or botrytis;
  • Maximize threat from pests and diseases;
  • Prevent transpiration or exchange of air for your plants;
  • Encourage unwanted microbiological growth;
  • Clog the stomata and reduce carbon dioxide intake, which is essential for efficient photosynthesis
  • Make the roots dormant by diminishing their natural ability to take up water;
  • Slow down your plants’ nutrient uptake;
  • Minimize your plant yield

Then it’s time to understand how you can maintain low levels of humidity in a grow tent.

Importance Of Low Humidity In A Grow Tent 

Humidity levels depend on the growing stage of your plant, but it’s advisable to know that low humidity in your grow tent can work wonders.

High levels of humidity and moisture build-up in a grow tent can cause your flower or buds to rot.

Other issues with high humidity are:

  • White mold: can pester your leaves, obstructing them from taking in water, air, and light.
  • Rust fungus: will cause rust spots on your leaves
  • Root rot: roots start rotting if the soil stays too moist for too long.

Grow Tent Size 

One of the first things you must review is the size of your grow tent, because you must ensure that all areas are covered by relatively low humidity.

For instance, a 4×4 grow tent requires 40% while a 5×5 grow tent needs at least 65%. 

I’m able to use a residential dehumidifier in my 4×4 grow tent, so a compact dehumidifier that can absorb 8 to 10 ounces of moisture on a daily basis works on a 2×2 grow tent.

What’s the best grow room temperature?

Measuring Weed Temperature

Temperature varies, but it’s needed to give you an idea on how to control humidity. Make sure you have a handy thermometer and hygrometer.

Clones or seedlings prefer 74-78 degrees Fahrenheit whereas vegging plants can thrive at 70 degrees Fahrenheit.

Flowering plants require higher temperatures of 88-75 degrees Fahrenheit than those ready to be harvested, which are good with 65-74 degrees Fahrenheit.

What’s The Best humidity level?

Plants thrive in different levels of humidity during all stages of their life.

Seedlings or clones need 70% to 75% humidity because plants need time to let their root systems develop, thus making them rely on their leaves to absorb water.

Feeding your baby plants means having plenty of moisture in the air. This is why indoor growers use propagation trays or humidity domes to build up moisture.

Vegging plants need 50% to 70% humidity because they now have the ability to take up water both from their roots and leaves.  

Flowering plants need 40% to 50% humidity to achieve a comfortable environment to breathe.

Harvesting in grow tent normally needs 45% to 50% humidity to ensure the environment isn’t too humid.

Humidity is an essential part when it comes to indoor gardening. Gardeners must learn how to fully control humidity levels, especially how to lower it in grow tents.

As growers, we should be aware of what levels of humidity are suitable for different stages of plant growth and certain plant varieties.

Finally, we should have the ability to combine different ways of lowering humidity in a grow tent to maintain relative humidity at recommended levels.

Humidity along with temperature and light can help growers raise healthy and robust plants with high productivity.

Here How To Lower Humidity In Grow Tent

As I’ve explained earlier, high humidity is important, but it could also cause harm when levels become extraordinarily high.

To help you reduce humidity in a grow tent, here are proven and simple ways that indoor gardeners have done:

1. Avoid overwatering your plants

Avoid Overwatering Your Plants

One of the most uncomplicated ways to decrease humidity levels is by protecting your plants from overwatering, which can make the water soggy or damp.

Overwatering results in more water that could increase humidity in your grow tent beyond appropriate levels.

Likewise, soggy soil will leave extra water in propagation trays, which could have a similar effect in raising humidity levels.

2. Use a Dehumidifier Inside your Grow Tent

Use A Dehumidifier

I’m sure you’ve met our old friend, the dehumidifier.When your grow tent is too humid, a dehumidifier can remove excess moisture in the air, thus helps in lowering humidity levels.

Okay, so this is something you probably have to spend more on because a grow tent typically needs a commercial dehumidifier. But hey, we must invest in resources to ensure overall plant growth and yields.

If your location is already humid, I suggest using a quality dehumidifier that is connected to a drain. 

If you live in an area with less moisture, it’s advisable to shut off the device and drain it whenever it is full.

Basically, your dehumidifier should be capable of removing at least the same amount of water your plants absorb daily.

Additionally, it is ideal to buy a dehumidifier that has at least one-gallon water tank capacity to save you time from filling it up often. Here how to choose proper dehumidifier size for your grow tent. 

I usually place my dehumidifier in the middle of my grow tent.

Some dehumidifiers have an automatic shut off feature when full. Nonetheless, you can also set a timer and monitor how much water your dehumidifier is collecting.

Consequently, both the inlet and outlet of a humidifier are placed inside your grow tent, which can cause the space to heat up.

3. Check your plant density 

Improve Ventilation By Adding More Fans

Plants naturally release carbon dioxide, which raises the temperature in your grow tent.As a result, moisture builds up and humidity increases.

Increasing the number of plants can displace the air in your grow tent, which prevents other areas from getting fresh air and carbon dioxide.Here how to figure out Ideal number of plants you should fit in your grow tent. 

Take note, water vapor transpired by your plants will be trapped if your grow tent has no proper dehumidification or ventilation.

If removing plants in your grow tent is not an option, consider moving only those plants that have extremely big leaves.

4. Remove stagnant water 

Remember when I said you don’t have to spend lots of money on trying to decrease humidity levels in a grow tent?Here’s one of the cheapest methods we can use!

As indoor growers, it’s our responsibility to make sure our grow tents have proper drainage so stagnant water won’t pool on the ground and add excessive humidity.

The problem with stagnant water is that it causes molecular oxygen to reduce to the phase where bacteria form and thrive.

One of our biggest mistakes is leaving water reservoirs exposed or letting stagnant water form puddles on the floor, which can release moisture into the air.You do not want your grow tent to become a breeding ground for pests and bacteria.

5. Improve ventilation by adding more fans

Improve Ventilation By Adding More Fans

I recommend putting more exhaust fans or speed up the fan rotation in your grow tent to improve ventilation. Increasing ventilation is the most practical way to help elevate the amount of airflow in the grow tent.

If possible, use an atmospheric controller with a humidity setting to automatically set the fan speed to attain the level of humidity you desire.

It could also be as simple as venting a duct fan or opening a window to push moisture out of the grow tent.I’ve observed that this option only works to lower humidity if the intake air has a lower RH than the air in the grow tent.

This ventilation method will drop humidity levels since the positive pressure inside creates enough air movement to give a gentle breeze all over your grow tent. Bottom line, make sure that your outflow fan is larger than your intake one.

I should warn you about relying on oscillating wall fans alone; they can fail to secure air circulation because they can only reduce the temperature on the canopy.

Good airflow should come from a grow tent’s wall, top surface, and bottom surface.

I now suggest buying floor fans because they can pull air through the canopy and ensure equal carbon dioxide distribution.

Guaranteeing stable temperature and balanced humidity levels in your grow tent will lead to a successful harvest.

Based on experience, using a hygrometer controller to power fans is reliable automation.It increases efficiency rather than using a thermostat or timer.

6. Create air holes

Grow Tent Air Holes

Making wide or narrow holes in your grow tent can regulate the flow of air. To decrease humidity, create widened holes to ensure more air gets in than gets out.Be cautious not to invite unwanted light in.

7. Purchase an air conditioner

We all know that the purpose of an air-conditioner is to cool the air, thus lowering humidity levels.The device uses compression and gas to pull the heat out of the air.

The process creates condensation, which effectively removes moisture from the air as well.

However, large AC units tend to run on short cycles or brief periods, which will create an unreliable environment for your plants.

On the other hand, small AC systems can gradually raise the temperature. 

There’s also the issue of frequent fluctuations that can cause the temperature in your grow tent to soar.

A good air-conditioner will ensure cold air will frequently replace hot air. 

This can also be paired up with a fan to help keep a cool environment in your grow tent by reducing water vapor.

Thus, you must select the properly sized air-conditioner for your grow tent that can pull enough water from the air.

VIVOSUN Dehumidifier
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Remember to clean the filters because clogged ones prevent good airflow, which will then raise humidity.

8. Insulate and seal your grow tent

One of the things that can help you control humidity is ensuring your grow tent is properly insulated and sealed.

I use foam insulation to make a thick barrier between the outside environment and my grow tent.This lessens my worry that external factors will pose a threat to my plants.

9. Use grow equipment wisely

Let me remind you that grow equipment, like grow lights, can elevate the temperature in your grow tent.Purchase a grow light that doesn’t emit a lot of heat.

If your grow tent has a warm environment, turn the lights off to have a temperature drop.Letting your lights rest also helps you save on electricity bills.

10. Make use of absorbent soil 

Make Use Of Absorbent Soil

As indoor growers, we must be familiar with the different kinds of soil that are suitable for our plants. The key to reducing humidity in a grow tent is by using soil that is capable of keeping water underneath.

I suggest using sandy soil because it has the ability to minimize evaporation rates and the amount of water on the surface.

You could also opt for perlite, but sandy soil is cheaper. A friendly reminder to change the soil frequently.

I’ve also discovered that using lime or baking soda has the same benefits of using sandy soil.

As a major rule, avoid any material or soil that can create dampness. Always go for absorbent surfaces.

11. Consider defoliating your plants 

Here’s another budget-friendly route you can take. Leafy plants or plants that have massive leaves can raise humidity levels in your grow tent.

I usually try cutting down some leaves so the humidity won’t go beyond the recommended level.

To sum it up…

Indoor growers must monitor both humidity levels and temperatures, as well as how they impact each other. In this way, we can understand how environmental factors affect the growth and survival of our plants.

Generally, plants will find it difficult to transpire if both humidity levels and temperature are high.As a result, growth and development become slow.

Moreover, airflow is one of the major determinants of humidity in a grow tent. Increasing the flow of air lowers humidity while a decrease in airflow elevates humidity.

Humidity levels must be controlled to ensure quality growth and greater yields. Excess humidity at any stage of your plants’ growth can cause problems such as mold and mildew.

Remember, understand the environmental factors first; then decide whether you can spend extra cash and invest in an air-conditioner or dehumidifier.

If not possible, there are cheap methods such as using exhaust fans, a hygrometer controller, checking ventilation, or controlling plant density.

You can experiment on which methods I’ve shared will be most suitable in lowering humidity levels in your grow tent.

Your plants will thank you for investing in proper gardening equipment, ensuring excellent air flow, and controlling relatively low humidity for them.

Last Updated on May 22, 2021 by Lindsey Hyland