How to Increase Humidity in a Grow Tent

by Raymond Archambault
beautiful indoor garden

If you’ve noticed your plants begging for water by curling upwards, it might be time to increase the humidity in your grow tent. All indoor growers understand that humidity and temperature levels are the secrets to providing a great environment for your plants to thrive. Understanding how to boost and regulate the relative humidity (RH) in a grow tent can be the make or break.

Humidity levels that fall anywhere between 45% and 75% are perfect for plants to grow. However, if your tent has a minimum RH of 20% and a maximum RH of 40%, then you might lose your crops. These low levels result in poor development and stunted plant growth. In the long run, it causes lower yields and dampness.

For that reason, increasing the humidity in your tent is crucial by relying on simple techniques or a humidifier. In this guide, we’ll walk you through the ins and outs of how to increase humidity in a grow tent.

The Basics of Humidity

Humidity refers to the amount of water vapour in the atmosphere and can be measured in 3 ways.

  • Specific
  • Relative
  • Absolute

It can also be measured using a hygrometer that should be a gardener’s best friend. When it comes to indoor gardening, relative humidity is of utmost importance. It measures the amount of water in the air versus at a particular temperature. Although plants can thrive at various RH levels, it boils down to the temperature in your grow room or tent. It’s worth keeping in mind that the warmer the air, the greater the water vapour it can hold.

The Repercussions of Low Humidity in a Grow Tent

Plants rely on water as a coolant as they absorb plenty of water, with about 95% going to the plant’s vascular structure, the roots, and making its way out through the stomata. Only about 5% is channelled to cell regeneration and growth. The combination of dry air and high temperatures produces a high vapour pressure shortage between the air and leaves. Nevertheless, plants exchange gasses via the stomata.

As a result, that exposes your plants to the dry conditions of the outside world. Although your plants will attempt to absorb more moisture to counter the dryness, it makes it harder for them to survive. Growing plants feel the strain of the additional pressure they exert on the roots to absorb water and counter the low humidity. Furthermore, plant dehydration causes stomata closure, which prevents water absorption.

While lower humidity levels compel the roots to absorb excess water, it includes excess nutrients that might burn the tips of the leaves. Low humidity or the lack thereof may cause plant desiccation when exposed to spider mites, mould, and mildew.

Why is High Humidity in a Grow Tent Important?

For new growers, the thought of high humidity evokes fear, but seasoned indoor growers understand the benefits of high humidity, particularly during the growth stage. In a nutshell, exposure of plants to relatively high humidity aids in the absorption of more water required for survival. While plants absorb water via their roots, they can take up more through their stem and roots. Plants won’t get the opportunity to get enough water for their entire growth and development with low humidity or the lack thereof.

Grow Tent Size

Relative humidity should be between 20% and 75%. Therefore, if you have a four-by-four grow tent, you should maintain a humidity level of not less than 40%. For a five-by-five tent, the humidity should be at least 65%.

The Most Ideal Temperature for a Grow Tent

The perfect tent temperature differs based on the phases of plant life. It’s a no-brainer that humidity and temperature go hand in hand, which is why indoor growers usually invest in a hygrometer and digital thermometer to monitor readouts.

  • Flowering plants thrive from 75°F to 88°F.
  • Seedlings or clones flourish in 74°F to 78°F.
  • The harvesting stage requires 65°F to 74°F.
  • Vegetative plants thrive from 70°F to 78°F.

What Is The Ideal Humidity Level?

indoor garden with flowers

Source: Pixabay

Just like temperature, plants call for varying humidity levels in different phases of their lives.

  • Clones or seedlings require a humidity level of 70% to 75% as they are growing their root systems. Baby plants require an abundance of moisture in the atmosphere, which you can accomplish via humidity domes or propagation Maintaining high humidity levels elevates the success rate for your seedlings to root.
  • Vegetative plants thrive in 50% to 70% humidity as their roots have already developed. Nonetheless, they still require leaves for moisture absorption. Low humidity levels can slow down growth.
  • Flowering plants flourish in humidity levels ranging from 40% to 50% in a comfortable environment. At this phase, you can curb mould or mildew from growing by maintaining a fairly lower humidity.
  • Harvesting in a grow tent calls for a humidity level of 40% to 50% to prevent your harvest from becoming brittle and harsh.

How Relative Humidity and Grow Tents Can Boost Plant Growth

Using a climate controller and grow tent allows you to regulate the environment of your plants. Furthermore, you get control over the light cycles. Elevating relative humidity is easier in a grow tent with a small air volume. A grow tent allows you to cater to different types of plants year-round regardless of the climate zone, season, and weather conditions. It also provides the perfect environment for plants to take in nutrients.

Your grow tent will help in curbing harmful elements ranging from parasites, insects, and mould to mildew that can potentially harm your plants. Nevertheless, these would all still depend on the relative humidity of your grow tent. For that reason, you must know various ways of boosting the RH in your grow tent.

Best Ways on How to Increase Humidity in a Grow Tent

You can boost the humidity levels in a grow tent in the following ways.

1. Combine Young and Mature Plants

People commonly assume that mature plants take the air, light, and nutrients from younger plants. However, the RH in a grow tent will increase once you add plants, particularly large ones. They respire and generate more humidity. When your larger plants respire, they release water vapour coupled with carbon dioxide.

Resultantly, that feeds their smaller counterparts. Bigger plants boast increased stomata and larger leaves, which means they emit more water vapour after transpiration. Your growing plants can then utilize the water vapour. The trick is to avoid overcrowding bigger plants to make sure your growing plants receive an adequate amount of nutrients, air, and light.

2. Use A Humidifier In Your Grow Room

Investing in a humidifier means you can extract a cool mist and elevate the humidity levels in your grow room. That’s significant in the healthy development of your plants. Based on the size of your tent, you can increase the moisture level of your humidifier to between 50% and 65%. If your tent has a bottom and top shelf, position the humidifier at the bottom to prevent it from directly spraying mist on the grow lights.

However, it’s worth keeping in mind that you must regulate your humidifier because leaving it on maximum power in a confined space can result in excessive moisture in the atmosphere. If possible, we recommend investing in a humidifier with a built-in humidistat that allows the device to automatically shut off, or you can adjust it as per your desired moisture settings.

Additionally, invest in a unit that can house at least 6 gallons of water and has long-running power. The best humidifier for your grow tent will allow you to regulate the moisture output, temperature, and airflow.

3. Utilize Propagators

Although seedlings can naturally germinate, you can acquire a better success rate of healthy plant growth by increasing the humidity in your tent by utilizing propagators. Seasoned indoor gardeners protect their cuttings and seedlings in propagators such as those with a glass or polyethylene cover. It prevents the seeds from becoming excessively dry. These handy devices retain high humidity levels in your tent, making sure your seedlings won’t stress their root systems during their growth and development.

4. Set up Your Propagation

Buy an adjustable extractor that has a built-in thermostat. It controls the temperature by drawing the air. Next, put a bucket of water on your grow tent that will be transported into a humidifier via a hosepipe. Keep in mind that the method is best suited for cuttings and seedlings. The humidifier will elevate the RH in your tent through the extraction of a cool mist in it.

5. Hang a Set of Water Trays or a Wet Towel near Passive Air Holes

Putting a pan of water or hanging a wet towel next to the airways is a no-brainer. It will elevate the humidity by misting down your walls. As a result, abundant moisture can be absorbed into the air. Nevertheless, it’s worth noting that a towel typically dries up quickly and will need you to wet it again after a while. Additionally, a pan or pot of water won’t create your desired RH.

6. Eliminate Half of your Fluorescent Tubes

The typical solutions are the most overlooked. You can lower the temperature by getting rid of half of your fluorescent lights. Fret not as light intensity shouldn’t be an issue because your baby plants only require minimal light.

7. Adjust Your Extraction Fan Setting To Minimum

Venting a grow tent is crucial as it allows you to control or manage RH for your plants. With ideal ventilation, there’s an exchange of air out of and into your grow tent. Furthermore, fans facilitate proper air circulation to your growing plants. Resultantly, you avoid bacteria, fungi, and other harmful microorganisms from multiplying and being trapped in your tent. You can set your fan to a moderate speed to preserve the moisture at various phases of plant growth. However, the air will dry quicker than usual if your fan is set at a high speed.

Likewise, setting fans at high speed will curb the water vapour from settling on the surface of your plants’ leaves for absorption. Therefore, moisture doesn’t get to the plants, causing desiccation and dehydration. Additionally, you can reduce the number of fans required to increase the humidity level in your grow tent. We recommend 60% to guarantee relative humidity.

8. Utilize a Water Spray Bottle

Growers typically own spray bottles, so that should be a non-issue. It comes in handy for spraying water on the walls of your grow tent every evening and morning.

9. Lower the Surrounding Temperature

Learning the ropes of how to cool a grow tent to elevate the water vapour is the secret for indoor gardeners, yet it becomes an uphill battle when temperature regulation is involved. It’s worth noting that cold air sinks at the bottom due to its high intensity compared to hot air. A lower temperature usually implies that the air is fairly moist with a considerable amount of water vapour. Likewise, the intensity of UV light can aid in increasing water vapour. However, that’s only if it’s sufficient to allow water evaporation.

10. Choose a Swamp Cooler

It’s a lifesaver in reducing the temperature in your grow tent. A swamp cooler aids in cooling down the air while boosting the levels of humidity. It functions optimally in low humidity and overly high temperature.

11. Increase the Sources of Water in Your Grow Tent

It’s a cost-effective way of increasing the humidity in your tent. You can place trays filled with water right next to passive air holes or air intake tubing. Similarly, positioning damp sponges adjacent to growing trays gets the job done. The heat emanating from an air conditioning system or grow lamp can slowly evaporate the water in the sponges, increasing the humidity of your grow tent. Remember to utilize clean water to curb harmful bacteria or fungi from staying in your grow tent.


High humidity levels in your grow tent are the key to healthy and young plants. Keep in mind that regulating humidity means factoring in other aspects of indoor gardening such as light, temperature, and ventilation. Now that you know how to increase humidity in a grow tent, the ball is in your court to determine the most suitable conditions.


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