Increase and Decrease the Humidity Levels in Your Grow Ten


The humidity levels in your grow tent need to be closely monitored to maximize the results of your yield. If left unchecked, a humidity level that’s too low or too high will destroy your plants and ruin all your hard work.

Even the best grow tents available on the market need to be observed for non-ideal humidity levels.

A good rule of thumb to remember when planning your first operation and to follow forever after is this: growing plants prefer humidity around 60%.

 As we stated above, a level too low or too high is going to cause issues.

If your humidity starts to get below the 60% mark, your plants will begin to dry up, their leaves will curl, and your batch will become bitter and stale.

If your relative humidity gets too high and stays high, then mildew and mold will begin to grow on your plants and ruin the harvest.

In both situations, the plants will be ruined, and you will have wasted precious time. What you should do instead is educate yourself on humidity, and how to control the relative humidity inside your grow room or tent.

In this article we’ll be teaching you exactly that: the most effective ways to control humidity in the confined space you have your grow operation growing in, and talk a little more about the positives and negatives of learning, or not learning, how to control the relative humidity level.


So, keep reading to find out more and make sure you’re not making some disastrous mistakes.

Why Bother Maintaining a Consistent Humidity Level

Some growers tend to believe other factors are more important when it comes to a successful grow. Factors such as temperature level and moisture levels. These factors absolutely do matter. But, humidity is definitely overlooked, and is in fact influenced by and influences these other two mentioned factors (temperature and moisture levels). ,

Take this example: a rise in temperature will cause the air to hold more moisture which in turn leads to a higher humidity level. If these levels increase too much than the plants will be almost “choking” on the high moisture levels, and experience a serious decline in growth. Eventually, they will stop growing and begin to prematurely die.

That would be a waste of good plants!

Do you know how many first-time and novice growers mess up this very important factor during their first few grows?

Too many, and their plants and yields suffer for it. Maybe they get a good looking yield out of these poorly grown plants. But, they won’t realize just how much they left on the table by not paying close attention to humidity levels.

So, why should you pay close attention to humidity levels in your grow tent or grow room?


  • Plant growth slows dramatically
  • Plants will die prematurely if bad levels continue unchanged
  • Best case scenario, your yield is okay, but not the best it could be.
  • Worst case scenario, all plants die and your yield ends up in the garbage.
  • Either way, your time is wasted

Now, what can you do to adjust the humidity, both in terms of increasing the humidity if the level is too low, and decreasing the humidity if the level is too high for plants to grow properly?

How to Increase and Decrease the Relative Humidity in Grow Tent/Room

First off, you need to get a temperature and humidity monitor for your grow room. A monitor is an inexpensive and professional way to track the always changing temperature and humidity levels in your grow room. If you have a serious interest in successful grow operations, you will need one of these monitors.

By the way, it’s called relative humidity because it’s relative to the conditions outside the grow tent or room. In your natural climate the air could be really dry, really wet, or really cold.

You get the idea: to have a proper grow operation with a great yield you need to maintain ideal growing conditions for the plants.

 Plants are similar to humans when it comes to water consumption: they need a lot of water too, but most of the water doesn’t stay in their system. The roots suck up all the water, and it passes through.

If the humidity gets too low in a grow tent, the air becomes dry and the plants won’t grow properly.

Here’s how to increase the humidity in a grow tent.


Humidifier – A humidifier will allow you to add more moisture to the air. There are many differnet types of humidifiers. Evaporative ones work very well for grow operations.


Swamp Cooler – A swamp cooler not only increases the humidty, but also decreases overall temperature. It’s a two for one.


Water Your Plants More – This one will take more skill experience with grow operations. The problem is you may end up watering them too much. On the other hand, your problem could be you’re not watering your plants enough. This is a low-risk way to see.

Here’s how to decrease the humidity in a grow tent:

Increase ventilation – you will need more exhaust fans and this requires the necessary vent holes in your grow tent. If you have the vent holes, additional exhaust fans will send some of the moisture out that helps cause a higher amount of humidity.

Limit the Amount of times you water plants – Unlike increasing the humidity, less watering will do the opposite and should help decrease the humidity.

Slight Defoliation – Keeping your plants trim will help the airflow in the grow tent. Also, the larger leaves encourage higher levels of humidty because of their size.


Increase Size of Grow Tent – A different approach and a good idea if you don’t want to trim your plants too much. You might be expanding too quickly for the size of your grow tent. Those leaving the “beginner stage” of growing will run into this problem faster than they think. Too little space for the plants doesn’t allow them to “breath” as well, and the airflow will also suffer because of this.


Additional Methods

These other methods are less gadget involved, and more slight tweaks you can make to your grow tent to see if any changes are made in the humidity levels inside.

Remember, this is a constant process. Many different factors can affect a grow. It’s your job to figure out the root causes, which there could be many.

Here’ s some small tweaks you can make:


  • Insulate the grow tent more
  • Remove or add heat lamps and lighting
  • Put bowls or plates of water inside the tent or near the fans (to increase humidity, of course)
  • Move bigger plants out of the tent to decrease humidity; reintroduce them inside grow tent if you need to increase humidity.


Final Thoughts

Having a successful grow operation means you will need to watch many different factors while your plants grow.

Temperature inside the grow tent is one.

Moisture levels are another.

Lighting and ventilation are more, and often the most taken care of by beginner growers.

Then there’s humidity, which we went over in length in this article.

If left unchecked the humidity levels in your grow tent could decrease or increase to a point that will affect their growth. Continued neglect will result in dead plants, or a bad yield.

Remember this: The humidity levels in your grow tent need to be closely monitored to maximize the results of your yield. Even if you have one of the best tents on the market you can’t let things go on autopilot until you have a system in place (most likely after years of experience).

Learning about the different environmental factors that can affect your plants will in fact save you time. You won’t waste time growing plants that end up drying up or dying out. You will be saved from getting frustrated and losing time.

Get a humidity and temperature monitor today. Then, once you’ve assessed your situation you can begin to plan what you need next.

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