How to Control Humidity in a Grow Tent

By Millie Traynor

Achieving optimal grow tent humidity levels is critical to the success of your plants. Different crops prefer different levels of humidity and getting the levels wrong can cause a reduction in yield or even plant death. In addition to affecting growth, the wrong humidity can affect the final product of the plant. 

So, you don’t want the humidity in your grow tent to be too high or too low. But what is the right balance and how do you control it? 

Here’s a guide to controlling humidity in your grow tent:


1. Finding Relative Humidity


It is important to understand the science behind humidity. This will give you a solid grounding to understand how to control the humidity in your grow tent.

Ultimately, humidity is the water vapour found in the air.  This is a fancy word for ’how much moisture is in the air’. The more water vapour there is, the higher the humidity. So when you attach a hygrometer to your growing systems and see 70% relative humidity (RH), it means that there is 70% of moisture in the air. This will feel like slightly damp air to the touch.

Relative humidity (RH) is the ratio of the current absolute humidity to the highest possible humidity. It allows us to understand how close the air is to saturation. To determine relative humidity, add the current absolute and dew point together. Saturation occurs when the current amount of water vapour in the air reaches 100%. At this point, any additional water becomes condensed but does not increase the humidity level because it has already reached saturation. Relative humidity is the air that is completely saturated with water vapour and cannot hold it any longer.

Water vapour is always in the air. The air will hold a high volume of water vapour when the temperature in your grow tent is higher. It is relatively easy to understand this when you consider that it gets hotter in your grow tent, the air becomes warmer and can hold more water vapour. Heat causes the water to move faster through the air, resulting in higher humidity.


2. Understanding When the Humidity is Too High


In a hydroponic setup, it’s important to control the environment. This includes everything from pH Levels to humidity. Depending on what you are growing, you will need to ensure you have the correct humidity level in your grow tent. Different plants have different humidity requirements (you will have to research this yourself). However, as a general rule, the humidity levels should be within certain levels at different stages of the plant's life cycle.


Germination/Cloning: Rh 75-85%

The initial growth of the plant’s roots takes place at this point, meaning a high humidity level is necessary.  A higher level of humidity now will help the root system to develop correctly and result in a larger, stronger plant. Humidity domes are often applied to a grow tent to increase the RH of the imminent air above the seedlings.


Vegetation: Rh 40-60%

At this stage, it is important to have a relatively high humidity level. Partial portions of the water consumption are conducted through the roots as well, but since they’re not fully developed, leaves need to keep intaking water.


Flowering: Rh 35-50%

At this point, high RH might start to harm the plant. It’s important from this point in the growing process to ensure there is no rise in humidity. High humidity levels can cause mould, rotten buds, and other plant defects.

To begin with, relative humidity should be within 40-50%. But as the buds start to produce a harvest, you will need to lower the humidity levels down to 35-40%.

Also, remember to reduce the humidity gradually - as opposed to a sudden drop in RH - as this can spoil your grow.


3. How to Lower Humidity in a Grow Tent 


Any step you take to lower your grow tent’s humidity levels will take time. This is important as sudden changes can harm the plants. However, the quickest way to safely lower the humidity is to use a dehumidifier.

Before concluding this is the best process for you, make sure your grow room has the right size implemented. You must consider these things before going ahead with this system:

- Your dehumidifier needs to have the exact dehumidifying capacity that your grow system requires. This is usually measured in how       many litres of water it will pull out of the air every hour.
- If you live in an area with high humidity, make sure your dehumidifier is able to attach to a drainage system. There also needs to be a     large enough water tank for this solution.
- The dehumidifier needs an automatic timer or shut-off feature when the tank is full.
- It should not optimise too much electricity.


      Once you have clarified that your dehumidifier meets the above requirements, your system is good to go. At Ashton Horticulture, we have an extensive range of humidifiers. Here are two of the best humidifiers on the market: 

      Humidistat Station
      Opticlimate 10000 Pro 4 

          4. How to Control Humidity in a Grow Tent 


          Ventilation is an essential part of controlling the humidity in your grow tent. If you don’t ventilate your growing space, then you can’t expect proper air circulation, which means no evaporation or drying out of moisture. As such, it’s important to ensure that there are plenty of holes in the grow tent so that moisture can leave.

          If you’re growing in a cold climate and have a harsh winter, then make sure to seal up all of your vents when it gets too cold outside. This will preserve your temperatures inside the grow tent, which is important for growing plants, keeping them warm enough at night but also allowing them to cool down during the day.

          This will make sure that moisture doesn’t enter or leave your grow tent, so you’ll need to ventilate it at a later point in time. Remember to seal up vents when it gets warm as well. This is important for maintaining the temperature inside the grow tent.

          Check out our grow shop to view our Dehumidifier and Cooling system products

          For assistance with all hydroponic products, contact us here. 

          Older Post Newer Post

          Just added to your wishlist:
          My Wishlist
          You've just added this product to the cart:
          Go to cart page