How To Control Humidity When Growing Indoors?
- Combining Young and Mature Plants
- Using A Humidifier in The Grow Room
- Using Propagators
- Building and Customizing Your Propagation Set-Up
- Hanging A Wet Towel or Setting Water Trays
- Getting Rid of Half Your Fluorescent Lights
- Setting Your Extraction Fan Setting to The Lowest Level
- Using the Water Spray Bottles
- Lowering the Nearby External Temperature
- Swamp Coolers Are Also Beneficial
- Stocking Up Water Sources in Your Grow Room/Tent
- Installing Air Conditioning systems
The use of grow tents is increasingly becoming popular today. It brings a range of benefits such as space maximization, year-round gardening, and conversation of energy. Besides, the farming technique also ensures the circulation of clean air, eliminates pests, and optimizes lighting. Some people opt for it due to ease of set-up and operation.
Grow tents primarily put you in complete control of your farm regarding water, lighting, and other requirements of efficient farming. As a great farmer, you can quickly realize when your plants begin facing water insufficiency. But if learning how to increase humidity in grow room or how to raise the humidity in grow room is one of your goals, then read on to determine some of the practical tips.
In summation, to keep your grow room humidity in check, you must:
- Ensure it is properly sealed and insulated.
- Monitor lighting and maintain a specific temperature range.
- Increase the cool air supply.
- Make sure stagnant water pools don’t form.
- Use an appropriately sized dehumidifier.

Humidity Basics
Humidity refers to the amount of water vapor held in the air. As an indoor grower, you can measure the element in three ways, namely relative, absolute and specific. You should also invest in a good hygrometer as it comes in handy in your gardening tasks, including measuring humidity.

Indoor farming majorly focuses on relative humidity, RH. The humidity section entails measuring the amount of water in air vs the maximum amount of water that can be held in the air at a specific temperature.
Plants flourish at different RH levels. However, the temperature of your grow room is still crucial considering that warmer air holds more water vapor. It would help if you also remembered that plants use water as a coolant. Minimal (about 5%) of the water they absorb goes into the building of new cells while the rest is lost into the air via the stomata.
Combining high temperatures and dry air results in a high vapor pressure deficit between the air and plant leaves. The plants, on the other hand, need to exchange gases through their stomata. The situation exposes the plants to dry conditions similar to the external world. Despite the plants’ efforts to acquire more moisture to deal with the drying effect, they find it difficult to survive and grow.
The optimum humidity in the greenhouse, grow box or indoors is 65%.
Effects of Low Humidity in Grow Tent
Water plays a significant role in the growth and development of plants. As a farmer, you must ensure an adequate supply of water in your grow room. Low humidity in the grow room causes stunted/poor growth and development of the plants. You should understand how to lower humidity in grow tent even though it results in dampness which lowers your yields in the end. Therefore, it would help if you worked towards raising the humidity in your grow tent anytime your plants show indications of water insufficiency. Several signs indicate low humidity in grow tent. There are three major ones that you should look out for, as highlighted below.
Low humidity in your grow tent forces your plants to draw excess water from the medium. When the humidity levels in the grow levels run too low, your plants eventually suffer insufficient humidity effects. They are forced to close their stomata to minimize excessive loss of water which results in a growth halt.
Low relative humidity (RH) forces your plants to draw too much water from the growing medium via the roots. The increase in water uptake by the roots comes with more intake of nutrients. Excess nutrients are not suitable for your plants as they eventually result in nutrient burns on the leaves. Plants that experience low RH also weaken and may die with time.
You can learn how to raise the humidity in grow room using a humidifier. Some simple tricks that require readily available materials at home should also be handy. Through this post, I explore a range of different but cost-effective techniques that I’ve used to create and raise the humidity in grow room. Discussed below are my favorite options that you should try out.
Simple Ideas on How to Increase Humidity in Grow Room
As mentioned above, getting a maximum harvest from your grow tent entails ensuring an optimum supply of all growth requirements. Some of them include water, lighting and warmth. This post primarily focuses on how to lower humidity in grow tent, create and raise it as well.
Before setting up your grow room for your next project, you should take time to understand how to create and increase humidity in grow room. It would help if you tried out some of the tricks and ideas I have used over the years, as highlighted below. Please find a few within your budget that meets your needs and focus on them for outstanding results.
Combining Young and Mature Plants
There is a common notion that bigger plants deprive the younger plants of water, light, air and nutrients. The case is different with grow tents, whereby the relative humidity increases with an increase in plants (especially the bigger ones). Bigger plants respire more which translates to higher relative humidity. Higher respiration by the bigger plants increases the amount of carbon (IV) oxide and water vapor utilized by the smaller plants.
Bigger plants also have bigger leaves. The leaves have more and bigger stomata which allow them to lose more water via evapotranspiration. Your grow room eventually boasts of more humidity which the smaller plants can utilize. When adding your plants into the grow room, you should be keen not to overcrowd them. Proper spacing of your plants is essential to ensure adequate access to the necessary resources. Overcrowding results in competition for resources among the plants, which compromises your yields in the end.
Combining Young and Mature Plants – Using A Humidifier in The Grow Room
One of the most significant investments that you should make as a grow room farmer is buying humidifiers. Humidifiers promote the humidity levels in grow tents by extracting cool mists, which is vital in the growth and development of plants. Based on the size of your grow rooms, you can increase your humidifier’s moisture level to between 50% and 65%. For grow rooms with both top and bottom shelves, the bottom shelf is the ideal place to place your humidifier. That way, it does not directly spray the mist on your grow lights.
Pro-Tip: You should always control your humidifier to over-humidifying the air in the grow tent. Leaving the equipment one full-power under confined settings causes too much moisture in the room.
Humidity Controller
It is also advisable to choose humidifiers with inbuilt humidistats. The feature is responsible for automatically starting and cutting machine operations based on your humidity needs. Over the years I have been doing grow room farming, I have found humidifiers with a long-running power and high-water holding capacity (at least six gallons at a time) ideal. It would be best if you were so keen on the choice of your humidifiers as the most suitable ones are responsible for controlling the airflow and temperatures besides the moisture output.

Using Propagators
While seedlings are capable of germinating naturally, raising their access to humidity enhances their success rate. Using propagators is another valuable technique for increasing- humidity levels in your grow tents. It would help if you were keen to protect your cuttings and seedlings when using this technique.
Propagator Set
Pro Tip: Consider reputable brands of propagators that come with extra valuable features. Some are designed with glass covers and polythene sheets which prevent seedlings from drying out. By maximizing the humidity levels in your grow room, the humidifiers prevent your seedlings from stressing their roots during growth and development.

Building and Customizing Your Propagation Set-Up
There’s a little experiment that perfectly works for me. I have an adjustable extractor designed with an inbuilt thermostat responsible for controlling temperatures by sucking out the air. I place a bucket of water on me grow tent’s top shelf, which is then siphoned into the humidifier via a hosepipe. The technique is ideal for cuttings and seedlings. The humidifier increases the relative humidity in the grow room through the extraction of the cool mist inside the room.
Pro-Tip: There’re many experiments that you can create based on the available resources. Find what works for you and maximize on it.
Hanging A Wet Towel or Setting Water Trays Close to The Passive Air Passages
Another simple trick suitable for increasing humidity in your grow tent is to hang a moist towel or place a water pan near the air intakes. The technique works by increasing mist down on the walls, which eventually raises the tent’s moisture.
Pro Tip: Be sure to wet the moist towels as they quickly dry up constantly. Pots and pans may not necessarily create your desirable relative humidity levels in the grow room.
Getting Rid of Half Your Fluorescent Lights
This is one of the proofs of how the common and most straightforward solutions are most overlooked. Fluorescent tubes increase temperatures in the grow tent. Eliminating about half of them reduces the temperatures, which means more moisture in your tent. The light intensity should be the least of your worries as baby plants do not require lots of high-intensity light to grow.
Setting Your Extraction Fan Setting to The Lowest Level
Venting your grow tent is an effective way of managing and controlling the relative humidity for your plants. Proper ventilation ensures a perfect exchange of indoor and outdoor air in the grow room. Besides, fans promote the circulation and distribution of air to the growing plants, which enhances their growth and development. Additionally, the constant circulation and distribution of air should help prevent harmful microorganisms. The microorganisms such as bacteria and fungi cannot survive or multiply in the tent due to proper air circulation.
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When using this technique, I aim at creating a balance between proper air circulation and the conservation of moisture in the tent. The most effective way of attaining the balance is setting my fans to run at a moderate rate. That way, my grow room remains adequately moisturized and ventilated.
Pro Tip: Setting your fans at high speed makes the air dry faster, lowering the grow tent’s humidity. High-running fans also prevent water vapor from settling on the plant leaves surfaces which reduces the absorption amounts. Your plants are susceptible to desiccation and dehydration due to a lower supply of moisture.
Minimizing the number of fans in use is also a significant way of raising the humidity in your grow tent. I recommend running the fans at 60% for ideal relative humidity.
Using the Water Spray Bottles
Water spray bottles are another vital but straightforward investment for you as an indoor grower.
You can use them to increase the relative humidity in your grow tent by spraying water on the walls of your tent regularly.
Doing so every morning and evening is the most effective schedule, especially for busy people.

Lowering the Nearby External Temperature
Understanding how to cool your grow room to raise the water vapor is essential for every indoor grower. It is, however, challenging to attain the goal anytime temperature regulation is involved. It would be best if you understood that cold air is denser than hot air.
Lowering the temperature makes the air in the grow tent relatively moist, which translates to higher humidity in the space. You can also increase the amount of water vapor by decreasing the intensity of UV light. If you choose the technique, you should be keen to ensure that the light allows water evaporation.
Swamp Coolers Are Also Beneficial
My experience as an indoor grower has also taught me the importance of swamp coolers. I primarily invested in the devices as a means to lowering the temperature in my grow room. The devices are suitable for cooling down air which increases humidity levels in the tent. The best time to use these coolers is when your grow tents are experiencing low humidity and extremely high temperatures.

Stocking Up Water Sources in Your Grow Room/Tent
Another simple and cost-effective way to raise the humidity in a grow room lies in filling your water sources and distributing them adequately. My schedule entails placing the water trays next to passive air passages and air intake tubes.
I also place damp sponges next to the growing trays, which work perfectly as well. The heat from the AC system or grow lamps gradually evaporates the water from the sponges. The air in my grow tent absorbs the water vapor evaporating from the sponges making the space more humid and moisturized.
Pro Tip: Always use clean water in the grow tents to avoid the growth and habitation of fungi and bacteria in the space.
For safety reasons, I do not recommend dampening sponges close to fans and lighting items. Grow lights and fans use electricity, and their contact with water may result in short-circuiting.
Installing Air Conditioning systems in your grow tents to reduce temperatures
You can also increase the humidity in your grow room by raising the temperature of the AC or reducing the temperature of the heater. Despite being one of the most effective, it is also costly, especially if you are cautious about your energy bills. It is worth considering by indoor growers with limited options.
Reasons Why High Humidity Is Essential for Your Grow Tent
High humidity may sound frightening or unbelievable to most new growers. Based on my long-term experience as an indoor grower, I assure you that high humidity levels are essential for your grow tent. The growing phase is the most critical and requires the highest levels of humidity.
Maximizing the humidity levels in your grow tents allows your plants to absorb adequate moisture that they need for survival and growth. Plants primarily take up water via their roots. Their stems and leaves may also be helpful for absorption in some particular cases.
Plants absorb water in water vapor from the air through small openings on their leave surfaces known as stomata. Lowering humidity in the grow tents thus reduces the amount of water absorbed by such plants. Insufficient water supply, as mentioned above, results in stunted growth and development and eventually lower yields.
High relative humidity levels are essential for the fast growth of healthy plants in your grow tent/room. As an indoor grower, you are in control of moisture, light, and warmth to ensure your plants’ incredible growth and development. Taking good care of the plants guarantees you satisfactory yields as well. Controlling and managing humidity in your grow tent involves a range of other gardening factors. The factors include ventilation, temperature, light and warmth.
There are various cost-effective and straightforward techniques that you can use on how to raise the humidity in grow room, as outlined above. Since every indoor farm is unique and has different needs, what works for another person may not work for you. I’d advise you to find what works for you from what I’ve explained above and maximize on it.
It would help if you also were keen on how to lower humidity in grow tent when it becomes excess for optimum growth of the plants. Both too high and too low humidity are dangerous for the growth of your plants. Strive at keeping your grow tent humidity levels at optimum for proper growth and development of the plants.
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Humidity in grow tent during flower?
It is rather subjective. If you want your plants to stay shorter, then keep the RH lower (I use 50% when growing outdoors). Higher percentages tend to favor lateral growth instead of height. The higher the RH, the more dense your yield will be also so don’t go over 70%. You can get by on less than that if necessary however.
Can thermostat control humidity?
The thermostat can control humidity by turning on dehumidifiers and fans.