Have you seen your plants begging for water? Have you noticed the leaves of your plants curling upwards?
Knowing how to control and increase the relative humidity in a grow tent is something that indoor gardeners must learn. Checking temperature alone won't suffice because overlooking humidity can affect your produce.
Humidity levels of around 45% to 75% are ideal for growing plants. But if your grow tent is only at 20% to 40%, you must now take action or risk losing your plants. I remember having no knowledge about how to increase humidity in my grow tent or grow room, which resulted in my plants drying out.
Low humidity inside a grow tent causes stunted growth and poor development of your plant. It could lead to dampness and lower yields in the long run.
This is why you must raise the humidity in a grow tent. This can be achieved by relying on a humidifier or simple tricks using materials found in your home.
In this post, we're going to explore the different, yet cost-friendly methods I've tried over the years to ensure your plants grow in relatively high humidity.
Humidity is the amount of water vapor held in the air. There are three ways to measure humidity-- absolute, relative, and specific. You can also measure it using a hygrometer, which actually should be one of your best friends when gardening.
Since we're into indoor gardening, we focus on the relative humidity. RH measures how much water is in the air versus the maximum amount of water that can be held in the air at a certain temperature.
Plants can thrive at different relative humidity levels, but it would still depend on the temperature in your grow tent. Remember, the warmer the air, the more water vapor it can hold.
Consequences of Low Humidity in a Grow Tent
Okay, time to review general science! Plants use water as a coolant. They absorb a lot of water, with about 95% going to the roots, the plant's vascular structure, and then exiting through the stomata. Only about 5% goes to building new cells.
A combination of high temperatures and dry air create a high vapor pressure deficit between the leaves of your plants and the air. However, plants need to exchange gases through the stomata.
This then exposes your plants to the dry conditions of the outside world. Your plants will try to get more moisture to counter the drying effect, but this measure makes it harder for plants to survive.
Growing plants become stressed from the extra pressure they exert on the roots to take up water and counter humidity deficit. Plant dehydration also leads to stomata closing, which causes the plant to unable to get more water.
Lower levels of humidity force the roots to take too much water, but it includes excess nutrients that could burn the tips of the leaves.
Lack of humidity also poses the possibility of plant desiccation, where the plant becomes exposed to infestation by insects such as molds, white powdery mildew, and spider mites.
Importance of High Humidity in a Grow Tent
For new growers, high humidity could sound frightening. Take it from experienced indoor growers, we've witnessed how high levels of humidity in a grow tent is beneficial, especially during the growing phase.
Basically, exposing your growing plants to relatively high humidity helps your plants absorb the water they need to survive. Plants take up water through the roots, but they could also get more through their leaves and stem.
As mentioned earlier, plants suck up water through water vapor in the air through the tiny opening on the leaf surface called stomata.
Plants will not have the chance to get sufficient water for their complete development and growth if there's little to no humidity.
Things to Review
Grow tent size
Heads up, relative humidity shouldn't be lower than 20% and must not exceed 75%. So, if you have 4x4 grow tent, you probably have to maintain at least 40% humidity while a 5x5 grow tent might need 65%.
The Best Temperatures for an Indoor Grow Room or grow tent
Ideal grow tent temperature varies on the stages of plant life. As I've emphasized earlier, temperature and humidity work hand in hand.
Indoor gardeners naturally invest in a digital thermometer and hygrometer to help them track readouts.
- Clones or seedlings prefer 74-78 degrees Fahrenheit.
- Vegging plants prefer 70-78 degrees Fahrenheit.
- Flowering plants prefer 88-75 degrees Fahrenheit.
- Harvesting phase normally requires 65-74 degrees Fahrenheit
What Is The Right Humidity Level?
Similar to temperature, plants require different levels of humidity in various stages of their life.
- Clones or seedlings must have 70% to 75% humidity because it's the time where they grow their root systems. Your baby plants need plenty of moisture in the air, which can be achieved using propagation trays or humidity domes. Keeping high levels of humidity increases the success rate for your clones to root.
- Vegging plants require 50% to 70% humidity since they've already developed their roots. However, they still need the help of leaves to absorb moisture. Low humidity levels can result in slower growth.
- Flowering plants yearn for 40% to 50% humidity to thrive in a comfortable environment to thrive. In this stage, you can prevent mildews or molds from forming by maintaining a relatively lower humidity.
- Harvesting in grow tent usually requires 45% to 50% humidity to ensure your harvest will not become harsh and brittle.
How Grow Tents and Relative Humidity Can Help You Grow Plants
Using a grow tent gives you more control over the growing environment of your plants. It also helps you control the light cycles.
Furthermore, increasing or lowering relative humidity levels is easier in a grow tent that has a small volume of air.
A grow tent allows you to take care of several plant varieties throughout the year regardless of the season, weather conditions, and climate zone. It also provides an ideal environment for plants to absorb nutrients.
Your grow tent will aid in preventing potentially harmful elements such as insects, mildew, mold, and parasites from causing harm to your plants.
However, these would all still depend on the relative humidity of your grow tent. This is why it's crucial you must know different ways of raising the relative humidity in your grow room or grow tent.
12 Easy and Cheap Ways to Raise Humidity in a Grow Tent or grow room
1: Combine Mature and Young Plants
It is a common notion that larger plants will take the light, nutrients, and air from the younger ones. On the contrary, the relative humidity in a grow tent will elevate once you start adding plants, especially large ones, because they respire more and produce more relative humidity.
When your bigger plants respire, they release products such as carbon dioxide and water vapor, thus feeding their smaller counterparts.
Larger plants boast bigger leaves and more stomata, meaning they can discharge more water vapor after evapotranspiration. Your growing plants can then use this water vapor.
The key is not to overcrowd the larger plants to ensure your growing plants get a fair share of air, light, and nutrients.
Use a Humidifier inside grow room
Buying a humidifier has been one of the best investments I've made. A humidifier aids in elevating humidity levels in a grow tent by extracting a cool mist, which is significant for the development of your growing plants.
Depending on the size of your grow tent, raise the moisture level of your humidifier to at least 50% to 65%.
If your grow tent has a top and bottom shelf, place the humidifier on the bottom part so it won't directly spray mist on the grow lights.
But I have to warn you that you must control your humidifier because leaving it on full-power in a confined space could cause too much moisture in the air.
If possible, buy a humidifier that has a built-in humidistat, which enables the machine to automatically shut off or cut in according to your desire moisture settings.
I strongly recommend buying a humidifier that can take up at least six gallons of water at a time and has a long-running power.
If you find the best humidifier for your grow tent, it will definitely help you in controlling the temperature, airflow, and moisture output.
Make Use of Propagators
Seedlings can naturally germinate on their own, but you can attain a greater success rate of growing plants by raising the humidity in your grow tent using propagators.
Notice how indoor growers protect their seedlings and cuttings in propagators.
Propagators such as EarlyGrow 70738 Medium Domed and a sheet of polyethylene or glass cover seeds from drying out.
They can retain high levels of humidity in your grow tent, ensuring your seedlings will not stress their root systems while developing and growing.
Build your own propagation set-up
Here's a little experimentation that worked for me. I've bought an adjustable extractor with a built-in thermostat that controls the temperature by pulling out the air.
I then placed a bucket of water on top of my grow tent. The water is transported into a humidifier using a hosepipe.
This method is suitable for seedlings and cuttings. The humidifier will raise the relative humidity in the grow tent by extracting a cool mist inside the grow tent.
Hang a wet towel or set trays of water near passive air holes
One of the obvious options you can take is hanging a wet towel or putting a pan of water near air intakes, which will mist your walls down and raise humidity. This allows a large amount of moisture to be absorbed into the air.
However, a towel has the tendency to dry up fast and will require you to wet it from time to time. In addition, a pot or pan of water won't necessarily create your desired relative humidity.
Remove Half of Your Fluorescent Lights
Alas, the common solutions are the most overlooked. You can reduce temperatures by eliminating half of your fluorescent tubes.
Don't worry, light intensity should not bother you since your baby plants don't need much light yet.
Set your extraction fan setting to minimum
Venting a grow tent is vital because it can help you manage or control relative humidity for your plants. Proper ventilation makes sure that there is an exchange of air in and out of your grow tent.
Moreover, fans let the air circulate well and get distributed to your growing plants. As a result, you can avoid harmful microorganisms such as fungi and bacteria from increasing or staying inside your tent when there's proper circulation of air.
I normally set my fans at a moderate speed to conserve moisture at different stages of plant growth. A word of caution, the air will dry faster than normal if you set fans at high speed.
Similarly, setting fans at high speed will prevent the water vapor from settling on the surface of your plants' leaves for absorption.
As a result, moisture is kept away from the plants, which can cause dehydration and desiccation.
You can also try reducing the number of fans to raise your humidity in your grow tent. I suggest setting the fans at 60% to ensure relative humidity.
Buy a water spray bottle
Growers usually own spray bottles, so this shouldn't be a problem. Another easy method you can do is by spraying water on the walls of your grow tent every morning and evening.
Lower the surrounding temperature
Learning how to cool a grow tent to raise water vapor is a know-how for indoor gardeners, yet it becomes challenging when temperature regulation is involved.
Keep in mind that cold air sinks at the bottom because of its high density than hot air. A lower temperature usually means that the air is relatively moist and has a substantial amount of water vapor.
Similarly, dropping the light intensity of ultraviolet light can help increase water vapor, but only if it is sufficient to facilitate water evaporation.
Opt for a swamp cooler
I use a swamp cooler sometimes to lower the temperature in my grow tent. The device helps to cool down the air and increase humidity levels simultaneously. It operates when humidity is very low and the temperature is extremely high.
Stock up on water sources in your grow tent
Another cheap way to increase humidity in a grow tent is by boosting up your water resources and distribute them accordingly. I usually place water trays next to an air intake tubing or passive air holes.
Likewise, putting damp sponges next to growing trays works well. The heat from a grow lamp or an air-conditioning system can gradually evaporate the water in the sponges, adding more humidity in your grow tent.
A friendly reminder to use clean water to prevent harmful fungi or bacteria from staying in your grow tent. It goes without saying, do not place damp sponges near lighting materials and fans for safety. Fans and grow bulbs use electricity and may short circuit when they come in contact with water.
Reduce temperatures by adding an air conditioner to your tent
To attain high humidity in your grow tent, gardeners simply increase an air-conditioner's temperature or reduce the temperature of the heater.
Well, it could be costly, but it's another way to try if you are out of options.
In conclusion, high levels of humidity in your grow tent is essential for the growth and health of your plants. Bear in mind that controlling humidity means considering other indoor gardening aspects such as temperature, ventilation, and light.
All of the options I've explained above are cost-effective, and you just have to determine which is more suitable for the conditions of your grow tent. You can buy a humidifier or air-conditioner, yet you may also use the tools commonly found in your home.
Generally, higher temperatures will make a humid environment while cooler temperatures will cause less moisture in the air. So, you might have to experiment on the different ways of increasing humidity in a grow tent. But surely, you'll discover what works best for you.
Lindsey Hyland grew up in Arizona where she attended University of Arizona’s Controlled Environment Agriculture. She has supplemented her formal education by working on various organic farms, including spending a semester abroad in India.
Growing and/or raising just about anything gets her excited. She is especially passionate about environmental justice and low-tech, sustainable ways to better run small-scale farms and homesteads. Lindsey started Urban Organic Yield to discuss gardening tips and tactics.