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How Humid Should a Grow Tent Be and Ways to Control It

Having a grow tent is a very beneficial tool. It does not take up much space, and it allows you to grow plants during any time of the year. If you decide to grow plants in a grow tent, one factor to look at is the humidity of the grow tent and how to control it.

The humidity of a grow tent should be between 40 and 75 percent. The stage of growth correlates to the humidity level: in early stages, you want the humidity to be closer to 70-75 percent. As your plants grow, it’s better to decrease the humidity to 40 percent to create ideal growing conditions.

Read on to find out more about humidity in your grow tent, why it’s important, and how you can control it.

Photo of a blue rain tarp with water droplets shimmering in the sun.
Photo by Rob Van Hal

How Humid Should a Grow Tent Be?

Grow tents are controlled environments. Their design makes them optimal for growing plants inside without worry about pests and other things which may harm them. Humidity is a key factor in making a grow tent viable and successful.

The humidity of a grow tent should only be high during the initial stages of growth. This occurs during the planting stage. During this stage, the seedlings need higher levels of moisture to strive. After this stage, however, the humidity should never be this high.

There are three main stages of the growing process. When you have a grow tent, you need to be aware of these stages as each stage requires a different humidity level. They are as follows:

  • Planting Stage. This early stage requires the moisture level in the air to be around 70 to 75 percent. This high level of humidity allows the seedlings to take root in the soil and these young plants need a lot of water to survive.
  • Vegetative Stage. During this stage, the humidity level should be between 50 and 70 percent. Take note of the gradual decrease in humidity as the plant gets bigger. It is during this stage that the plant is beginning to sprout leaves, so it has more ability to take in the water content.
  • Flowering Stage. This late stage is when the plant is in full bloom. The humidity level should stay between 40 and 50 percent.

If you stick to these guidelines for each growing stage, paired with the proper temperature and light within the grow tent, your plants will strive.

Why is Humidity in Grow Tents Important?

Plants need water to grow and survive, and they absorb water not only through their roots but also through their leaves and their stem. Humidity is the moisture content in the air. In the summer, a lot of plants outside grow because the humidity is higher.

When you have a grow tent, you control the environmental conditions for your plants. Too much or too little humidity will harm your plants, which is why it is important to monitor the humidity level in your grow tent. Make sure that the levels are in the ranges required for each growing stage of your plant.

If you do not monitor the humidity level, the levels may rise above or fall below where they should, which could lead to:

  • Brittle plants. This happens when the humidity level is too low. With not enough moisture being supplied to the plant, the leaves and flowers can become brittle and break.
  • Burnt-looking plants. When the humidity is too low, the plants are working overtime trying to find water. As a result of this exertion, the plants’ leaves can become discolored or burnt.
  • Weak plants. Without enough humidity, the plants are weaker and more susceptible to disease.
  • Mold. If the humidity is too high, the plants become breeding grounds for mold and bacteria of all sorts. Bacteria love moist environments to live and grow in. If the humidity is too high, mold could take over the plant, killing it in the process.

It is important to maintain the proper humidity to avoid these issues. For plants to grow successfully throughout a growing season in a grow tent, an ideal growing atmosphere must be maintained.

How to Increase the Humidity in a Grow Tent?

To measure the humidity in your grow tent, you will need a hygrometer. A hygrometer measures the humidity level in the air and using this reading will help you decide whether you need to raise or lower the humidity in your grow tent.

Depending on which stage of the growing process you are in will determine what constitutes an ideal moisture level. If you find that your levels are too low, you will need to increase the humidity in your grow tent. But how do you do this?

There are a few ways you can increase the humidity in your grow tent.

  • Get a humidifier made specifically for a grow tent. This is the best option to control and raise the humidity in your grow tent. These units are readily available and easy to find. A smaller unit will work better as it will not oversaturate the air, especially in a more confined space like a grow tent.
  • Readjust the ventilation system. Your grow tent has a ventilation system that may need to be readjusted slightly. This will allow more moisture to stay within the tent than being taken out.
  • Water. This is not the best option, but it can be a quick fix while you work on the other methods mentioned here. Simply put a bowl or other container of open water within the grow tent and place a fan in front of it. This is not a precise way of doing it but can be used as a Band-Aid. 

How to Lower the Humidity in a Grow Tent?

If your hygrometer measures a high moisture level, you might need to lower the humidity of your grow tent to the proper level. There are several ways to do this:

  • Use a dehumidifier for your grow tent. As with humidifiers, there are dehumidifiers made specifically for grow tents. These units will decrease the moisture level in the air in your grow tent.
  • Create better ventilation. You can either readjust your ventilation system to allow for more airflow, or you can create your own air holes in your grow tent. Either adjustment will allow more airflow which will help the extra moisture leave the interior of the grow tent.
  • Do not overwater your plants. One way that can help maintain perfect humidity is to avoid overwatering your plants. Some of the water you add to the plants’ soil evaporates into the air. If you find the humidity levels are too high, consider cutting down on how much water you are adding to your plants.
  • Use a different soil. Different soils retain varying amounts of water. There are soils that are more absorbent than others. You want a loamy, well-draining soil that will not be as absorbent, which will cut down on the moisture level within the grow tent.
  • Space the plants apart. If possible, try and space your plants apart. If they are too closely packed, then more moisture can be trapped within them, which can raise the humidity. By spacing them out, you are helping with the airflow between the plants, which will help keep the humidity down.

Closing Thoughts

Humidity plays a crucial role in the success of a grow tent. Plants need moisture to survive, but they require different amounts during different times of their growing process. It is important to keep this in mind when you are maintaining your grow tent.

Make sure to measure your humidity levels consistently with a hygrometer. By monitoring it in this way, you will always know when you need to adjust the humidity, or when it is just right.