How to Lower Humidity in a Grow Tent

by Raymond Archambault
indoor garden

As an indoor grower, keeping the relative humidity in check is no easy feat as it can result in a host of problems. It’s a lot more complicated than just throwing a humidifier in there. Seasoned gardeners understand that the highest humidity level in your grow tent is crucial for the growth of indoor plants.

Excess humidity in your tent means that you need to lower it. High humidity levels can trigger stunted growth, mold, bud rot, powdery mildew, and fungal growth. It’s these factors that threaten the survival of your plants, including your likelihood of high yields. Your grow tent humidity shouldn’t exceed 70%.

Therefore, if you’re surpassing this level, you must determine the origin of the moisture and control humidity levels to prevent it from damaging your plants. The good news is, maintaining a low humidity level can be resolved by the contents of your tent. In this guide, we’ll delve into how to lower humidity in a grow tent without denting your wallet.

Understanding Relative Humidity (RH)

Humidity refers to the water vapour found in the air. Relative humidity encompasses the ratio of the highest possible absolute humidity to the current one. In a nutshell, RH is the point when the air is saturated by water vapour to where it cannot accommodate it any longer. It’s worth noting that there’s always water vapour in the atmosphere. The air houses more water vapour as a result of increased temperatures in your grow tent. Heat in the tent causes the faster air circulation of water in the atmosphere, leading to raised humidity.

What Are The Repercussions of High Humidity?

The common assumption is that high humidity is imperative in ensuring the healthy growth and development of your plants. Although it’s a no-brainer that plants thrive in high humidity, too much of anything does more harm than good. Therefore, to avoid the grow tent from:

  • Making your flowering plants suffer from botrytis or bud rot
  • Preventing the exchange of fresh air for your plants (transpiration)
  • The perfect breeding ground for mould and bacteria
  • Encouraging unwanted microbiological growth
  • Diminishing your plant yield
  • Reducing the intake of carbon dioxide as a result of clogged stomata. It’s essential for optimum photosynthesis.
  • Optimizing diseases and pests
  • Slowing down the nutrient uptake of your plants
  • Making the roots dormant by reducing their natural ability to absorb enough water
women watering indoor gardening plants

Source: Pexels

Why Humidity Is Important In A Grow Tent

Humidity levels vary based on the phases of your growing plants. Nevertheless, it’s recommended to keep in mind that low humidity in your tent works like a charm. High levels of moisture buildup in your tent may result in the rotting of your buds or flowers. Other issues that stem from high humidity are:

  • Root rot. It’s whereby the roots begin rotting if the soil retains moisture for an extended period.
  • The white mould can pester your leaves and prevent them from absorbing light, water, and air as they should.
  • Rust fungus that results in spots of rust on your leaves.

Grow Tent Size

Factoring in the size of your grow tent is important because you need to make sure that all areas are covered by relatively low humidity. For instance, a five-by-five tent requires at least 65%, whereas a four-by-four needs at least 40%.

Best Grow Room Temperature

Although temperature varies, it comes in handy to give you an idea of how to regulate humidity. Ensure you have a build-up or thermometer in hand. Seedlings or clones gravitate towards 74°F to 78°F whereas vegetative plants thrive at 70°F. Flowering plants demand a higher temperature range of 75°F to 88°F compared to those that are ready for harvesting (65°F to 74°F).

How to Lower Humidity in a Grow Tent

Here are some simple and proven techniques seasoned indoor growers rely on to lower humidity in a grow tent.

Don’t Overwater Your Plants

Protecting your plants from overwatering is one of the easiest ways to lower the humidity levels in your grow tent. Overwatering leads to more water that increases humidity beyond the recommended levels. Similarly, soggy soil will leave extra water in propagation trays that might increase humidity levels.

Rely on a Dehumidifier

When your grow tent is overly humid, a dehumidifier comes in handy in eliminating the excess moisture in the air. As a result, the humidity levels decrease. Keep in mind that you might need to invest in a commercial dehumidifier to get the job done effectively, preferably one connected to a drain, if you live in an area with higher humidity. If you reside in an area with less moisture, we recommend shutting off the device and draining it each time it’s full.

Your dehumidifier should be capable of eliminating the same amount of water that your plants absorb every day. Furthermore, purchasing a dehumidifier with a water tank capacity of at least 1 gallon is perfect for saving you the hassle of frequent refills.

Monitor the Density of your Plants

Plants emit carbon dioxide that increases the temperature in your tent, which results in humid air and moisture build-up. Increasing the number of plants can displace the air in your tent and prevent others from getting the carbon dioxide and oxygen they need.

It’s worth noting that the water vapour your plants transpire will be trapped if your grow tent lacks sufficient a ventilation system or dehumidification. If eliminating some plants from your tent isn’t an option, you can move only those with large leaves.

Get Rid of Stagnant Water

Sometimes less water is better. It’s your responsibility to make sure that grow tents have the proper drainage required to prevent stagnant water from pooling on the ground and adding excess humidity. The issue with stagnant water is that it results in the reduction of molecular oxygen. In turn, bacteria don’t form and thrive. One of the common mistakes growers make is letting puddles of water collect on the ground or leaving water reservoirs exposed. These release moisture into the air and the last thing you need is for your tent to become a breeding ground for bacteria and pests.

Boost Ventilation with More Exhaust Fans

Proper ventilation is one of the most practical ways to aid in elevating the level of airflow in your grow tent. If possible, we recommend using an atmospheric controller that has a humidity setting to adjust the fan speed and acquire your desired level. Nevertheless, it can be as easy as opening a window or venting a duct fan to eliminate excess moisture. You can also use inline fans or floor fans if the space allows for it.

Keep in mind that this method is only effective if the intake air has a reduced RH compared to the air movement in the grow tent. The ventilation technique will work wonders in diminishing the humidity levels given that the positive pressure inside generates adequate airflow for a gentle breeze all over the tent. This method boils down to ensuring your outflow fan is bigger than your intake one.

Create Air Holes

Making narrow or wide holes in your grow tent can maintain the airflow. To lower humidity levels, create wide holes to ensure more air gets in and fewer escapes. However, tread carefully as the last thing you need is excess light.

Buy an Air Conditioner

It’s a no-brainer that an air conditioner comes in handy in cooling the air and as a result, lowers humidity levels. The process creates condensation that effectively gets rid of moisture from the air. It does so by using gas and compression to extract heat from the air. Nevertheless, large AC units usually operate on brief periods or short cycles that create an unstable environment for your plants. Contrarily, small AC systems can slowly increase the temperature.

Additionally, there’s the issue of regular fluctuations that can cause a spike in the temperature in your tent. A great air-conditioner will substitute hot air with cold air. It can also be paired up with a fan to aid in keeping cool conditions in your tent through the reduction of water vapour.

Therefore, you must opt for an appropriately-sized air conditioner for your grow tent that can draw sufficient water from the air. Don’t forget to clean the filters at least once a month. Clogged filters deter great airflow, raising the humidity.

Seal and Insulate Your Grow Tent

One of the things that can aid in controlling humidity is making sure your grow tent is properly sealed and insulated. Use foam insulation to create a thick barrier between your tent and the outside environment. By doing so, external factors that can damage your plants become the least of your worries.

Use Grow Equipment Appropriately

Keep in mind that grow equipment such as grow lights can boost the temperature in your grow tent. If your tent has a warm environment, switch off the lights to lower the temperature. In turn, you also cut down on your power bill.


Indoor gardeners must regulate temperature, humidity, and how they interrelate. As a result, you can grasp how environmental factors impact survival and plant growth.  Usually, plants will find it an uphill battle to transpire if temperature and humidity levels are high. In turn, that slows down their development and growth. Additionally, airflow is one of the considerable determinants of humidity in a grow tent.


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