Indoor Humidity Control for Medicinal Plants

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. Grow tents primarily put you in complete control of your farm regarding water, lighting and other requirements of efficient farming. If learning how to increase humidity in grow room or how to raise humidity in grow room is one of your goals, then read on to determine some of the practical tips.

Learning how to control humidity in a grow tent is an essential part of indoor growing.

Why Does Humidity Control Matter?

Plants are constantly taking in water to absorb nutrients and grow to their full potential. Humidity changes how much water your plants take in. Since humidity changes how much water your plants drink, and the water you give your plants have nutrients in them, being in control of humidity gives you increased control over your plant’s nutrient intake.

Signs of High and Low Humidity

Too high humidity can cause mold and bud rot (ruining plants). Bud rot is the single biggest problem when it comes to humidity and growing. It makes plants completely unusable. 

White powdery mildew can show up on leaves in areas with high humidity environments. 

Too low humidity means slow growth and poor leaf development. 

Additionally, for optimal growing and plan production, the early stages require higher humidity levels than the rest of the growing cycle. It’s common to add a humidifier to grow spaces during the early clone growing stage, while a dehumidifier may be required later in the growing process. 

The Correct Humidity Levels for Different Grow Stages

Germination/Cloning: Rh 75-85%

At this stage, the initial growth of the plant’s roots takes place. So a high humidity level is mandatory. Humidity domes are often used to increase the Rh of the imminent air above the seedlings.

Vegetation: Rh 40-60%

Humidity has to be a bit high because grow plant leaves would require enough water in the air. A partial portion of the water consumption is done through roots as well. But as they’re not fully developed yet, leaves have to keep intaking water. 

Flowering: Rh 35-50%

This is the stage where high Rh starts to show it’s bad signs. So it’s very crucial from this point to ensure no raise in humidity. Otherwise, molds, rotten buds, etc will start to take place. 

At the beginning of the flowering stage, the Relative humidity should be kept within 40-50%. But as the buds start to produce a harvest, growers lower it down to 35-40%. And this has to be done gradually without any major, sudden drop in the Rh. 

Harvesting/Drying: 30-40%

At this stage, crops start to dry and result in harvest. But still, we have to keep a 30-40% humidity level not to let the buds dry too fast. Some growers love to stick to a bit higher humidity(50%) in order to let his buds dry slower. This is anyway, improves the quality of the cured buds. 

How To Lower Humidity In A Grow Tent

1. Do not flood your plants

At times, you may overwater your plants, probably because you feel the plants don’t get enough water. However, over-watering your plants will reduce their efficiency in carrying out transpiration depending on the temperature in the tent. When the atmosphere is saturated with water vapor, the rate of transpiration is slowed down to an extent that may not be healthy for the plants.

2. Use a dehumidifier

Wouldn’t it be wonderful if science came up with a machine that was designed specifically to remove moisture from the air, where all you would have to do is plug it in and walk away?

A dehumidifier is the simplest way to tackle the humidity problem, but they can be expensive if you have a large tent or bigger room. If you decide to go this route, just make sure to do your research and match the size of your area to the right kind of unit.

3. 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.

4. 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.

 5. Ventilate Your Grow Tent

Bring new air into the tent from the outside can help lower the humidity, assuming you do not live in an extremely high humidity area. Of course, if you are going to bring in new air from outside, this means you will also be exhausting air from the tent.

For small tents, you actually only need to blow air out of the tent. The resulting negative pressure will automatically suck new air in. To exhaust the air, you’ll want a good inline fan for your grow tent.

With larger tents, or to avoid tent suck, you need a fan to blow fresh air back into the tent, to replace the air you are sucking out.

Humid air is heavier than dry air, so if humidity is a huge issue and temperature is not a big problem, you might consider setting up an exhaust fan down low. Generally, it is better to put them at the top of the tent, though, since that is where hot air gathers.

How To Raise Humidity In A Grow Tent

 1. Using A Humidifier in The Grow Room

The easiest way to increase your humidity level or maintain a specific humidity level in a room with low humidity is to add a humidifier.

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.

2. 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. 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.

3. 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.

4. 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.


Humidity levels must be controlled to ensure quality growth and greater yields. Excess humidity at any stage of your plants’ growth can cause problems such as mold and mildew. Remember, understand the environmental factors first; then decide whether you can spend extra cash and invest in an air-conditioner or dehumidifier.

You can experiment on which methods I’ve shared will be suitable in controling humidity levels in your grow tent. Your plants will thank you for investing in proper gardening equipment, ensuring excellent air flow, and controlling relatively low humidity for them.

If you have more issues with your plants, do not hesitate could contact us freely.

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