How to control the humidity in Grow Tent?

How to increase humidity in grow tent is one of the most important issues faced by indoor gardeners. In this article, we will tackle how to control humidity in grow tent and also provide you with measures that will help protect your plant from dampness and drying out.

If you decide to raise your plants indoors, there are many things you should take into consideration. This is especially true when you raise them in a grow tent.

Grow tents gives you an opportunity to take care of different plant varieties all through the year without minding of the seasons. With them, you can grow any plant regardless of the climate zone or weather conditions.

Grow tents help you have a controlled environment which even allows you to make use of hydroponics instead of the conventional soil.

One of the major benefits of grow tents is that they provide a more efficient environment for nutrients absorption by the plants. Grow tents also keep at bay all potentially harmful elements of mother nature such as mold, parasites, mildew, extra dirt and insects larvae or eggs that would cause harm to your plants.

You will realize that majority of indoor gardeners concentrate on factors such as seed or seedling quality, growth PH, fertilizers, and system cleaning overlooking humidity of the grow tent. Moisture or amount of water vapor in the air is an essential factor you should keep in your mind to make sure you have healthy plants.

This article will take you through the role humidity plays in the growth of plants and all steps you should take to raise the humidity in hydroponics grow tent, in case the levels go too low. Since too high humidity is dangerous for your plants, you will as well learn how to lower humidity in grow tent.

Why Humidity Matters To YOU

In all stages of cannabis growth your plants will have a constant need to intake water, and the amount of water they need fluctuates with the humidity in your grow room. When the humidity is high, cannabis plants use their leaves to absorb moisture from the air which causes them to drink less water from their roots. Conversely, when the humidity is low, they will pull more water in through their roots.

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.

But controlling humidity isn?t just about prevention?having the right humidity encourages strong, healthy, leafy plants with vigorous growth. In fact, growing with DWC (Deep Water Culture) / Bubbleponics during vegetation with the correct humidity can actually turn into a struggle to tame out-of-control plant growth!

Additionally, after your plants start making buds in the flowering stage and get close to harvest, you can manipulate the humidity of your grow area to get your plants to produce more resin (trichomes/glitter which contain THC and other cannabinoids) while preventing plants from being attacked by mold. High humidity can sometimes cause mold or bud rot ? a grower?s worst nightmare for those fat, dense main colas.

How to Control Humidity in the Growroom

Control Your Temperature

When you grow marijuana outdoors in a suitable climate, you don?t have to worry as much about how the weather impacts your crop, unless of course there is an unseasonable spell of weather. For indoor growers, lighting is all-important. While it is tempting to blast your room full of powerful lights, you need to be wary because too much lighting causes the temperature in your grow room to soar.

A common mistake is to purchase an air conditioning system that?s far too large or small for the grow room. As a result, frequent fluctuations play havoc with the temperature. When it comes to AC and temperature change, short cycling and the deadband are the two key factors.

In case you?re not aware, the deadband is a 3?5? Fahrenheit range around the temperature that you have set the room?s thermostat to. When the temperature reaches the upper end of the deadband, your AC unit will turn on to keep the room at the right temperature. When the temperature reaches the lower end of the deadband, the AC switches off to stop the room getting too cool.

If your AC system is too large, it will run in ?short cycles?, which means it consumes a ton of energy and creates an unreliable growing environment where humidity and temperatures rise and fall rapidly several times a day. If your AC unit is too small, the grow room temperature will increase to an uncomfortable level for your plants. Above all else, marijuana plants thrive in a consistent climate, so short cycles can be disastrous for their growth.

Short cycles cause unwelcome spikes in temperature. As humidity levels are inverse to temperature, a boost in temperature leads to lower RH, and a fall in temperature leads to a reduction in RH. The resultant unstable growing environment becomes an ideal breeding ground for mold and mildew.

Therefore, the challenge for growers is to find a properly sized AC unit for their grow room. In an ideal world, your grow room?s temperature will look like a lengthy and shallow wave on a graph. Once you find the right size AC unit, it will pull enough water from the air to ensure there is minimal strain on your dehumidifiers.

Ventilation and Humidity in the Growrom

The most practical method of controlling humidity is often through ventilation. Humidity can easily be lowered by increasing, or raised by decreasing, the amount of air being exchanged throughout the room.

This is usually done by adding a can-style exhaust fan. To increase the effectiveness of the exhaust fan, an intake hole can be added or widened, resulting in an increased amount of air being moved through the room.

A light baffle may need to be constructed around the intake hole to prevent light leakage and still allow plenty of airflow.

For more reliable automation and increased efficiency, a hygrometer controller can be used to power the fan rather than a timer or thermostat. Because plants technically need fresh CO2 rather than constant fresh air, many rooms configured with CO2 injection systems have little or no ventilation.

Rooms configured in this fashion use dehumidifiers to control humidity and extra air conditioning to control temperature. The enclosed area and lack of ventilation causes a rise in humidity.

Furthermore, the increased metabolic rates the plants achieve from the added CO2 lead to increased transpiration and an additional increase in humidity. In this situation, a humidifier would not be needed.

Seal and Insulate Your Room

If you?re trying to grow marijuana in a dilapidated building, or else you live in an old, relatively uninsulated building, you?re doing it wrong! One of the key tenets to successful indoor marijuana growth is to ensure your grow room is properly sealed and insulated. In the modern era, commercial builders use foam insulation and other materials to create a thick barrier between the marijuana grow room and the environment outside.

If you live in an area where outdoor humidity is relatively low, you may think this tip doesn?t apply to you. However, it remains a necessity regardless of whether you live in Colorado or New Mexico because it stops external factors such as humidity, wind, and sunlight from adversely impacting your weed.

These three factors, along with a few others, have a significant impact on temperature. As we mentioned earlier, temperature and humidity levels are closely related. If you insulate your grow room properly, you don?t need to worry about outside factors damaging your crop.

Transpiration of Plants and Its Effect on the Growroom Environment

Plant density also impacts humidity levels. The air in the room is displaced by increasing the number of plants, which also act as windbreaks and prevent other areas of the room from receiving fresh air and CO2.

In addition to air displacement, additional plants cause a rise in humidity due to increased transpiration. Without proper ventilation or dehumidification, the water vapor transpired by the plants has nowhere to go. For this reason, as plant density increases in the garden, so too will ventilation needs.

In this scenario, if the exhaust fans cannot keep up with the high humidity created from increased transpiration, a dehumidifier may also be necessary. If the high level of humidity is not corrected, transpiration is hindered, and overall plant metabolic rates decrease.

To prevent lowered metabolism and the slowing of plant growth, keep in mind the impact of plant density and transpiration and be proactive by controlling humidity levels before these issues arise.

The Importance of Air Movement

Although humid air holds more water, it is actually lighter than the air that surrounds it. Therefore, it rises toward the ceiling of your grow room. Meanwhile, CO2, which is a critical component for plant growth, remains near the floor. As a consequence, your grow room must have excellent air circulation.

A lot of growers assume that oscillating wall fans are sufficient. In reality, they only reduce the temperature on the canopy and completely fail to provide air circulation. If you want a successful harvest,you need good air flow throughout the room. It must be coming from the walls and the top and bottom of the room.

If you can afford them, we recommend purchasing floor fans. They pull air through the canopy of your marijuana plants and guarantee balanced humidity levels, equal CO2 distribution, and a stable grow room temperature.

Humidity During Germination & Propagation

While germinating seeds or rooting cuttings, it is extremely important to keep humidity levels much higher than normal (80?90%) to promote initial root growth.

If humidity is too low, the vapor pressure deficit will encourage transpiration to occur too rapidly to allow energy for root development. A humidifier or ultrasonic fogger may be added to ensure relative humidity remains at an appropriate level.

Another useful tool to keep humidity levels high enough for seedlings or cuttings is a humidity dome, which can be placed over the young plants to create a micro-climate where humidity levels remain higher than ambient levels.

Another thing to consider while germinating seeds or rooting clones is that although the relative humidity needs to be kept much higher than ambient levels, the moisture level at the roots should be treated normally by giving them plenty of oxygen in between waterings.

Use a Correctly Sized Dehumidifier

One would imagine that purchasing a high-quality dehumidifier is near the top of a grower?s list of new equipment. In reality, however, too many individuals bizarrely go cheap and invariably end up paying twice. Does this sound like you?

As it happens, residential dehumidifiers are a waste of money because they are not designed to handle the level of moisture in a marijuana grow room. Also, they use a lot of energy and are extremely inefficient. For many growers, the cost of a commercial dehumidifier seems too high, but they are forced to pay eventually because of problems with humidity in their grow rooms.

Bear in mind that plants transpire all but 3% of the water they absorb. Therefore, you need to correctly size a dehumidifier to pull the right amount of moisture from the air. If you have a large grow space, you?ll probably need several dehumidifiers. Make sure you design the system so that if one unit stops working, the rest continue to operate smoothly. Although it probably seems expensive at first, you will save a lot of money on electricity compared to residential units.

We hope that this guide has proved helpful. It is important to remember that plants with Indica genetics tend to have dense buds and are more susceptible to bud rot in humid conditions than their Sativa counterparts. We recommend checking your plants regularly, and you should also invest in a high-quality thermometer and hygrometer. There are all-in-one thermohygrometers available.

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 a properly sized dehumidifier.


Gardeners need to pay close attention to temperature and humidity levels, as well as how they affect each other, to fully understand how environmental factors can impact plants. If both temperature and humidity levels are high, plants are not encouraged to transpire and growth slows.

To encourage transpiration and maximize growth potential, a greater VPD must be reached by either decreasing relative humidity or increasing temperatures. Because increasing temperature levels can further raise humidity levels and stress plants, the former is the most optimal choice.

If both temperature and humidity levels are low, plants are not encouraged to transpire and growth slows. To encourage transpiration and maximize growth potential, a greater VPD must be reached by increasing temperatures to a safe level while maintaining lower humidity levels.

Understanding VPD will not only enable a grower to make necessary corrections to the environment, but also anticipate environmental problems before their effect has negatively impacted their crop.

For maximum yields and quality, humidity levels need to be controlled with the use of a hygrometer controller, fans, and/or a dehumidifier or humidifier.

It is important to understand how temperature affects relative humidity and their combined effect on transpiration rates. Your plants will thank you for learning the roles these environmental factors play in the garden, and how and when to control them.


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