how to lower humidity in a grow room

How To Lower Humidity in a Grow Room

It’s important you keep the climate of your grow room at the right level, but should this change it’s important you know how to lower humidity in a grow room so that your plants can thrive.

Why Humidity is Important

Plants breathe like humans do but in order to breathe they require a specific level of humidity. Plants create this humidity by breathing out water vapour – known as transpiration – but if it is too humid the plant will not breathe properly and it will ultimately not grow very well. The level of humidity also affects how much water they take in and thus how many nutrients they take in.

If it’s too humid, plants will try to breathe water vapours back in from the air and will drink less water from the reservoir. This can also have a negative effect on the plants growth because it’s not taking in the nutrients needed to develop. Also, bacteria tends to develop and thrive in more humid grow chambers and this can harm your plant.

How to Lower Humidity in a Grow Room

There are four main ways to bring the humidity levels back down so that your plant can develop well. Knowing how to lower humidity in a grow room is extremely important and it’s quite common to have to combine the following methods.

Air Circulation

Installing a good air circulation system is vital to reducing the humidity level if it gets too high and also maintaining a good level of humidity in the grow room.

An air circulation system works by releasing hot air out of the top of the grow chamber, moving it through the air circulation system and returning it into the grow chamber (via a hole in the bottom) as cooler air. This helps to reduce the temperature in the chamber and thus reduce the humidity as the plant will breathe out less in a cooler environment.

Reducing the Heat

Although an air circulation system will help to reduce the humidity and the heat in your grow chamber by removing the hot air and replacing it with cooler air, it’s important that you prevent your chamber from getting too hot.

how to lower humidity in a grow room
How Temperature Affects Humidity

The type of grow light you use can cause the humidity to increase as they emit heat – which is why I recommend using T5 grow lights as they give out such little heat that they can be placed 2 inches away from the plant. If you’re not using T5 lamps, then I recommend that you position your lights further away from your plants so they don’t feel the heat as much.

Another great way to reduce the heat is to buy an oscillating fan as it will help with the air circulation whilst cooling the plant down. Remember, the best way to reduce humidity is to cool the plant down as the plant creates humidity by breathing out water vapour – something it does a lot more when it’s too hot.

Stop Watering Your Plants

Excessively water your plants can cause them to release more water vapour and thus make the air more humid so be careful not to over water your produce. Whilst it’s important to have great air circulation, knowing how to lower humidity in a grow room just by making simple changes to your plant maintenance is also useful.

Air Dehumidifier

If you aren’t too sure how to lower humidity in a grow room, an air dehumidifier will do the work for you. An air dehumidifier will pull moisture from the air and thus reduce humidity, allowing your plant to grow as it will be able to breathe more freely.

The best air dehumidifier for a grow room in my opinion is the VonHaus Compact Dehumidifier.

It’s size ensures it will fit perfectly into a smaller grow room but still be just as effective in a larger grow room. It can operate at 30° and 80% humidity, sucking on average 750ml of water out of the air per day.

As it has a 2 Litre water tank, you won’t be required to change the tank too often so you can just leave it to operate whenever you’re busy – you can also see the water level rising so you know when you need to change it. As indicated, the air dehumidifier has an auto switch which will turn the machine on and off whenever the humidity reaches a desired level, so you can leave it running during the night.

Allowing you to lower humidity in a grow room so you can grow high-quality plants even as you sleep.


Now that you know how to lower humidity in a grow room, it’s important that you ensure your grow room has the correct humidity for your plants to grow quickly and well.