Importance of Humidity for Growing Cannabis

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Added 27 March 2023

Ever visited a tropical island during the summer? The days are hot but they feel a lot hotter, making you sweat a lot, thanks to all that high humidity. 

On the other hand, when humidity is low, your skin starts feeling dry and itchy and even your lips may start flaking. 

If that is what humidity does to you, it’s easy to guess what it can do to your cannabis plants. Sure, it won’t make your plant itchy or lose its skin, but it can cause other problems like nutrient deficiencies, mold infestation, slow growth, etc. 

Humidity is one of the crucial factors that a grower needs to account for when growing cannabis, especially if they are growing the plant indoors. 

But how do you do that? 

Learn everything you need to know about humidity for cannabis plants in this article below.

Understanding Humidity for Cannabis

Understanding Humidity for Cannabis

Humidity is the amount of moisture present in the air, i.e., the higher the vapor quantity, the higher the humidity in your grow room. When growing cannabis, humidity mostly refers to relative humidity (RH), which is the percentage of humidity in the area. 

Relative humidity is a measurement that is directly related to the temperature — hot air contains more moisture than cool air. So, relative humidity is the moisture content in the air relative to the moisture content it can hold at its saturation point. 

The relative humidity is crucial for your plant’s transpiration, nutrient uptake, and terpene and cannabinoid production. It is one of the primary forces that drive your plant’s growth, health, and even potency. 

This relative humidity can have a tremendous impact on how your plant grows along with its potency, effectiveness, flavor, and much more. 

For example, if your grow room has high relative humidity, your plant is at a higher risk of developing mold or fungal infections. On the contrary, low humidity levels can cause your buds’ trichomes to dry out, reducing their potency.

Considering the importance of humidity in cannabis cultivation, you need to monitor and control humidity. Otherwise, if the humidity is left as is, your plant may continue to absorb the moisture even when it’s not needed, which can lead to further damage. 

If you are growing cannabis, you must know how and when to control humidity, but before we get into that, let’s take a look at some of the factors that affect relative humidity in your cannabis grow room. 

The Role of Humidity in Cannabis Growth                                 

The Role of Humidity in Cannabis Growth

The relative humidity is crucial, no doubt, but it can have a drastic impact on your plant if it is not set to the ideal levels. When you set the relative humidity right, your plant benefits and grows well due to better nutrient uptake and produces more terpenes and cannabinoids.

Cannabis needs to convert sugars into energy during the photosynthesis process, and in doing so, it also produces oxygen, which is released into the environment via the stomata. At the same time, it absorbs carbon dioxide. Some water is lost to the environment during this exchange. 

Relative humidity comes into action here to dictate how much water your plant will give out to the environment. Here, two situations can occur. If the air is too humid, the water concentration gradient decreases — your plant loses less water and stays in shape.

When the relative humidity is too low, the water gradient goes up, leading to more water loss, which can hamper crucial respiration processes. Relative humidity regulates your cannabis plant’s respiration and other subsidiary processes.

Factors that Affect Relative Humidity for Cannabis

Factors that Affect Relative Humidity for Cannabis

While many factors can affect relative humidity in your cannabis garden, the three primary factors that affect it are your location, your plant’s genetics, and its growth stage. These three factors tend to have the biggest impact. 

1. Region or Local Climate

The first factor that affects relative humidity is your region’s climate. For instance, if you live in a colder region, the air is less humid, and you need to increase the relative humidity in your grow room for optimal growth of your plant. 

On the other hand, if you live in a tropical region, you need to reduce the relative humidity since these areas tend to be more humid than what’s best for cannabis plants.

2. Genetics of Your Cannabis

Even if you have the most optimal relative humidity in your grow room for most cannabis plants, some cannabis strains may not fare well due to genetics. Some strains grow better in low or high humidity since they have evolved in those conditions. 

So, the relative humidity in your grow room also depends on the type of cannabis you are growing, i.e., its strain. You must know the humidity levels your strain prefers and finetune your grow room accordingly.

3. Growth Stages

The third primary factor that affects relative humidity is the growth stage your plant is in. When your plant is a seedling, it requires higher humidity levels since the roots have not grown so much, but as the root ball develops, you need to reduce the relative humidity in your grow room.

The relative humidity must be decreased further when your plant enters the flowering stage to keep the buds dry and free of mold or fungal infestations. 

Other factors that affect the humidity in your grow room include the number of plants, plant size, tent seals, air circulation systems, and light intensity. 

Ideal Humidity Levels for Cannabis

Ideal Humidity Levels for Cannabis

Relative humidity depends on the strain you are growing and your local region. For example, strains that originate from arid regions fare well in dry conditions and those from tropical ones require higher relative humidity for the best growth.

However, you can stick to a rough guideline, to begin with, and finetune the relative humidity from there. Here, you need to set the humidity levels depending on the growth stage your plant is in, which is divided into four stages. Let’s take a look at each one of them and their ideal humidity levels.

1. Seed Germination 

Humidity levels that are either too low or too high can impact the germination rate of cannabis seeds. For best results, cannabis seeds should be germinated in a humidity range of 70-90%.

2. Seedling Stage

When your cannabis plant is in its seedling stage, the best humidity levels are 65% to 70%. This high humidity allows the plant to consume water through the leaves since the roots are still developing. At the same time, high humidity allows the roots to grow faster.

This range applies to clones, too.

3. Vegetative Stage

When your cannabis plant enters the vegetative stage, the best relative humidity is between 40% to 70%. During this time, the roots of your plant will have developed enough to sustain the plant, so your plant will no longer need to consume water through the leaves. 

However, do not reduce the humidity levels from 70% (of seedling) to 40% in a day — that can cause shock to your plant. Instead, decrease relative humidity by 5% every week until you reach the 40% mark, and at the same time, gradually increase the temperature. 

If the leaves on your plant look too moist, you need to further reduce the humidity as that is a sign of high humidity. 

4. Early Flowering Stage

The ideal relative humidity level for a cannabis plant in early bloom ranges from 40% to 50%, which is relatively low but not low enough. During this time, your plant will get most of the water from the roots and some from the leaves. 

Do not keep the relative humidity above 50% as that can lead to mold or fungal infestation in your cannabis buds, which can completely ruin the yield.

5. Late Flowering Stage

When your plant transitions into the late flowering stage, the buds will start putting on weight and growing bushy. There won’t be enough airflow within the buds, so the chances of them getting mold increase.

This is why you need to further reduce the relative humidity between 30% to 40% during the last 6 to 12 weeks. Low humidity will also improve your cannabis buds’ flavor and potency!

6. Post Harvest

Once you have harvested the buds, you still need to monitor the humidity levels in your grow room. During this time, as your buds gradually lose moisture, maintaining the humidity is crucial. Here, if the humidity is too high, the buds may not dry fast enough and even develop mold. 

On the other hand, if the humidity is too low, the buds may dry a lot faster, which can result in a loss of potency and flavor. 

So, when you start out with the drying process, stick to a relative humidity of around 50%. After a few days, increase the humidity to 60% while lowering the temperatures. And during the curing process, stick to a relative humidity of 60% to 65%. 

The Effects of Wrong Humidity Levels on Cannabis

The Effects of Wrong Humidity Levels on Cannabis

As mentioned earlier, humidity is crucial for your cannabis plant. When it is not maintained to the optimal levels, it can cause significant issues for your plant that show up in various ways. Here are some of the ways wrong humidity levels can hamper your cannabis plant’s growth and even threaten the yield.

1. Bud Rot

One of the most infamous crop killers in the cannabis community is bud rot — it can easily destroy your entire crop with no chance of recovery. Bud rot occurs when the cannabis buds on your blooming plant develop mold in the cores. 

This mold infestation generally begins in the bud stem and spreads further outward, quickly overtaking the entire bud and covering it in white flakes (spores). This is caused due to the relative humidity being too high.

What makes bud rot worse is that it is often difficult to spot with the naked eye, and once it has infested your cannabis bud, it is almost impossible to get rid of it. It will turn your buds white, gray, and eventually black, and turn them into slimy balls. 

When bud rot occurs, the only thing you can do is cut your losses and toss the infected buds as the mold can spread to other buds in the vicinity quite easily. Plus, smoking or consuming rotten buds is never recommended — it can have nasty health effects on the user

2. Mildew

A similar predicament to bud rot is white powdery mildew, which is a fungal infection that can also occur when the humidity is set a little too high. Similar to bud rot, even this fungal infection can damage your buds to a great extent. 

Similarly, it is not recommended to use buds with mildew on them. It is best to toss the buds, cut your losses, and protect the buds that have not yet been infected by this fungus. 

3. Nutrient Deficiencies

When the relative humidity is low around your plant, your plant consumes water through the roots to keep itself healthy, especially if the weather conditions are warm. However, when your plant consumes too much water through the roots, it can suffer from nutrient deficiencies or lockout.

When this happens, your plant’s leaves develop burnt tips or start turning yellow. In severe cases, your plant may also lose vigor and mass, which will further affect its ability to produce energy via photosynthesis. This problem is more common during the flowering stage for cannabis.

4. Low Vigor and Growth

If the humidity levels are not maintained at ideal levels, your plant may eventually experience restricted growth as its nutrient and water absorption capabilities, along with photosynthesis, will get affected.

The result would be that your plant will not grow as fast as you would expect it to, and in severe scenarios, it may even stop growing entirely. This can significantly affect the quality of your plant’s yield, too. 

Here’s a quick summary of what happens when the humidity levels are wrong:

Wrong humidity levels can affect your cannabis plants negatively and ultimately impact the overall yield and quality of the crop. 

  • Low Humidity: Low humidity can cause cannabis plants to dry out and become stressed. Eventually, it can lead to wilting, leaf curling, and reduced growth. In severe cases, low humidity can cause the leaves to turn brown and crispy, and can even kill the plants.
  • High Humidity: High humidity levels can promote the growth of mold and mildew, which can quickly spread and damage the crop. Excessive moisture can also lead to root rot, which can weaken the plants and cause them to wilt.
  • Inconsistent Humidity: Fluctuating humidity levels can stress the plants and make them more susceptible to pests and disease. It can also impact the quality and potency of the final product.
  • Reduced Yield: Incorrect humidity levels can impact the overall yield of the crop. Low humidity can reduce the size and weight of the buds, while high humidity can cause the buds to become less dense and less potent.

As you can understand by now, maintaining the correct humidity levels is crucial for healthy cannabis growth and maximizing yields. Growers should monitor and adjust humidity levels regularly to ensure optimal growing conditions.

Ways to Control Humidity in Your Cannabis Grow Room

Ways to Control Humidity in Your Cannabis Grow Room

Growing cannabis is easy, but one of the aspects that can pose a challenge is controlling the humidity of your cannabis plant. If you’re growing outdoors, this is even more difficult since you virtually can’t control the environment.

But if you’re growing cannabis indoors, you can control the humidity, whether it is to make it lower or higher. By controlling humidity, you can ensure your plant grows well, avoid the risk of bud rot and mildew, and even improve the quality of yield. 

Here are some of the best ways to control humidity in a cannabis grow room.

How to Increase Humidity in the Grow Room?

If you want to increase the humidity in your cannabis grow room, you should try out some of these tips:

  • Use a spray bottle or a mister to manually increase the humidity in your grow room — not recommended since this won’t last long, but can work in a jiffy
  • If you’re using soil as a growing medium, keep it moist — not wet — to increase the humidity of the roots 
  • Increase the frequency of watering to increase humidity levels in the grow room. Watering the plants more frequently will increase the moisture in the air as well. However, be careful not to overwater the plants as this can cause other issues like root rot
  • Keep open water containers or hang damp towels around your grow room. The water will evaporate and add moisture to the air. Be sure to monitor the trays and refill them as needed.
  • Turn down the fans in your room, including the exhaust, so the warm air is not circulated 
  • Invest in a humidifier and ensure it has a large tank so you don’t have to refill it very often. There are various types of humidifiers, including warm mist, ultrasonic, and cool mist humidifiers

How to Decrease Humidity in the Grow Room?

On the other hand, if you want to decrease the humidity in your grow room, try out some of the following tips:

  • Turn up your fans and exhausts to push more fresh air inside and warm air outside. Increasing ventilation in the grow room can help to reduce humidity levels. By improving the air exchange rate, excess moisture can be removed from the room
  • Increasing the temperature of the grow room can also help to reduce humidity levels. Warm air can hold more moisture than cool air, so by increasing the temperature, you’re reducing humidity levels. However, be careful not to raise the temperature too much as it can affect the health and growth of your plants
  • Water your plants before you turn the lights on
  • Overwatering the plants can contribute to excess humidity in the grow room. Reduce the watering frequency and use pots with good drainage to prevent excess moisture buildup in the soil.
  • Invest in a dehumidifier. There are several types of dehumidifiers, including desiccant, refrigerant, and thermoelectric dehumidifiers

Follow these tips and you can easily tune the relative humidity of your grow room. 

How to Measure Humidity in the Grow Room?

How to Measure Humidity in the Grow Room?

Wait, how will you know what the relative humidity is before you fine-tune it?

You can do so in many ways. And this is an important step that must not be skipped. For this, you need a hygrometer, i.e., a humidity meter. This meter can help you detect the relative humidity in your grow room with ease. 

You can even invest in digital hygrometers that connect to other sensors and apps — these will help you monitor the humidity levels at a glance, and you can even connect them to smart devices to automate the process entirely. But even manual ones work just fine if you don’t want to invest a lot or bother with setting up an entire ecosystem. 

On the other hand, if you use devices like a humidifier or a dehumidifier, they usually have a humidity reader built-in that will let you know the exact relative humidity in your grow room.

When measuring the humidity levels in your grow room, it is advisable to measure it in multiple locations of the room instead of a single location to get a more accurate reading. 

More Tips on Controlling Humidity in Your Grow Room

To help you achieve better results, here are some nifty tricks that you can use to improve your grow room’s humidity regulation and control. Follow these tips and tricks:

  • Remove the lower leaves of the plant as soon as they begin to fade — this will improve the aeration within the lower canopy
  • If you’re cloning cannabis, the cuttings need to retain a lot of moisture so the roots develop well. Therefore, keep that in mind when controlling humidity during the rooting period for clones 
  • Invest in automated climate control, especially if your region experiences drastic temperature and humidity changes between day and night — this will drastically reduce the burden on you and streamline the process a lot more. 
  • Always keep a log of the temperatures and relative humidity in your grow room even if you are not facing any problems; this will help you figure out any problems and fix them soon 
  • Many growers use two hygrometers in a single room to measure relative humidity at better accuracy — not required but quite helpful 
  • Make sure your pots or containers drain well to avoid high humidity at the root zone even if the relative humidity of the room is low 
  • Always use humidity control systems that are designed for plants and not humans 
  • Always do in-depth research on the strain you are growing and the levels of humidity it prefers because some strains prefer high humidity whereas others do not

Relation Between Humidity and Temperature

Relative humidity must not be factored in on its own, it should always be considered along with temperature — both are closely related to each other. As mentioned earlier, warm air holds more moisture than cool air. So, your cannabis plant will grow well at different relative humidities as per the temperature of your grow room. 

If you want to learn more about this, look up vapor pressure deficit (VPD), which measures the temperature and relative humidity together. For example, the ideal VPD for cannabis is between 0.8 to 0.95 kPa. 

So, when you control the humidity in your grow room, you also need to control the temperature. Generally, cannabis plants thrive best in temperatures between 70°F to 80°F( 21°C to 27°C) during the day and slightly lower temperatures during the dark hours. 

Summary: Importance of Humidity for Growing Cannabis

Humidity must not be overlooked, especially in an indoor grow room or a greenhouse. The principles stay the same — if you can control the humidity, do it. Your goal as an indoor grower is to create ideal artificial conditions for your cannabis to grow well, and humidity is a part of it. 

While it may look overwhelming, monitoring and controlling humidity isn’t so hard. Know the ideal ranges (as mentioned above) and use a hygrometer to check the relative humidity in your grow room.

If the humidity is too low, use the tips mentioned earlier to increase the humidity and vice versa. And when you do so, make sure you regulate the temperature as well. 

Remember, humidity can either make or break your plant and its yield. Worst case scenario? Your buds develop mold or your plant does not grow well. No one wants that.

This is why you should always pay attention to humidity when growing cannabis for the best-case scenario. What is it? Flavorful, potent cannabis buds that will not give you a lung infection and a plant that grows fast without any nutrient problems. 


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Nice one!! 💚
Excellent text.
Nice info!
Interesting read, Was hoping it would have some info about RH when the light goes out, as what i witnessed is an increase of 10% to 18% of RH when the girls goes to sleep 💤 .... sensors in app sounds like my next expense 😆😂