How to Lower Humidity in a Grow Tent

Humidity levels in a grow tent can either help or diminish your wonderful plants from performing at their best. You want luscious, full, and very nice green leaves that are moist and lush without being too dry. You want vigorous stems, roots, and vines that don’t wither or break easily. You also want the soil to be a nice soft consistency that isn’t too wet or too dry.

Outdoors, natural wet weather like rain helps create the ideal environment for plants to grow. But indoors in grow tents, there is a big chance you will run into humidity problems.

Plants release moisture through their leaves, so it’s not just the water you’re adding to the soil when you water them that raises moisture levels. There are many other things going on and you may need to know how to lower the humidity in a grow tent.

Tell-Tale Signs of High Humidity

Tell-Tale Signs of High Humidity

How can you tell that you even need to lower the humidity? For those of you who own a hygrometer, there is an easy answer to this question. The hygrometer measures the humidity in a specific square footage area.

Full-grown adult plants will require a humidity level of between 55% and 60%. Younger plants will require a higher humidity level of at least 60% and possibly even up to 70% because their smaller leaves and stems release moisture at a faster rate than adults.

If your humidity levels are much higher than those percentages, your plants will let you know. The soil will feel wet, cakey, and water-logged. The leaves will feel too plump and will droop from having too much water in them. You will also run into the trinity of high humidity – mildew, mold, and rot.

This will also affect your living space outside the grow tent. You might even see mold or mildew on your walls and ceiling above the grow tent. It’s not only ugly and unsightly, it can be hazardous to the people living in the space as well.

You Will Need a Dehumidifier

Both humidifiers and dehumidifiers are wonderful machines that will quickly work to solve all but the most persistent humidity problems. A dehumidifier will work to remove the moisture from your grow tent. You want to find one that has the following two characteristics:

  • Covers enough square footage for your entire grow tent
  • Has a built-in humidistat to control the humidity percentage levels

It’s worth it to invest in a dehumidifier that has these two features. The humidistat is not just a convenience factor. You will program in the lower humidity level that you need. Then set up the dehumidifier to run. Once it reaches that pre-programmed level, the humidistat will alert the de-humidifier to shut off. If the moisture level then starts to run too high again, the humidistat will sense it with its built in sensors. It will let the dehumidifier know to turn back on and suck the moisture out.

A Proper Ventilation System Also Helps

Combine your de-humidifier with a regular air conditioner to keep the temperature down and a CO2 greenhouse regulator that helps ‘breathe’ carbon dioxide over your plants.

A Proper Ventilation System Also Helps

When you encourage more air to circulate among your plants, that encourages the moisture that is emitted through their leaves to move around in the space; this helps lower the overall humidity. You should have proper ventilation through pipes, air conditioners (if feasible), and window fans.

Combined with extraction fans, ducting pipes will bring in cooler air and remove the warmer, moister air. This process is called air exchange. It not only lowers the humidity, it lowers the temperature to prevent that ‘jungle’ feel, and it brings in fresh carbon dioxide for your plants to breathe in. Remember that they have to take in CO2 and then emit fresh oxygen.

These types of ventilation systems are better for smaller grow tents and grow rooms. If you have a larger space and are a serious grower, go the de-humidifier route instead.

The Grow Tent Greenhouse Effect

Unnaturally high humidity levels can start to create big problems in as little as 24 hours. It doesn’t take long for your plants to start to wilt and droop. Invest in a de-humidifier set up to ensure that your plants will have a safe and healthy level of humidity. It will also prevent the need for home repairs, mold removal, and even wood rot. Moisture is your home’s No. 1 enemy.

So keep the grow tent happy and balanced with a humidity level that suits your plants in your miniature greenhouse.

Leave a Reply 5 comments

Terry Parm - January 18, 2019 Reply

Good info. Lucky me I reach on your website by accident, I bookmarked it.

    VapeMaster - January 19, 2019 Reply

    Thanks Terry!

    smoretraiolit - April 15, 2020 Reply

    Hello! I just would like to give a huge thumbs up for the great info you have here on this post. I will be coming back to your blog for more soon.

Burt - February 19, 2019 Reply

That’s not a grow tent that’s a green house. Maybe if you actually grew your own you would know this, or at least have pictures to use.

    VapeMaster - February 21, 2019 Reply

    Hi Burt,
    Thanks for the comment and observation. I concede it does look like a more rigid structure than a grow-tent, but being an external soil based unit I think the structure needs to be better fixed but the poles and non-rigid cladding marks it as a sort of tent.
    I do agree that ‘greenhouse’ has become generic for external structures rather than just the traditional fixed and glass-clad greenhouse of old.
    I think we all agree that internal solutions are ‘grow-tent’ solutions and being protected by walls, can be very lightweight and not so rigid. What we wanted to try and convey is that growing can be contrasted between hydroponic and soil-based systems and soil usually means an external ‘climate- controlled’ environment and usually a more commercial and scaled up approach.
    My growing experience is limited but the purpose of the site is to share information, not just from me and the writing team’s experience, but from many sources of value so that we can give the best information we can to our visitors.
    If we do make, or feature, the occasional mistake, we do appreciate being told about it and I also apologize in advance 🙂
    In reference to valuable information for those able to do more on the growing front where this is now legal (which I am not able to do here in China) I do recommend the ILGM ‘Grow Bible’ by Robert Bergman. Cheers and thanks!

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