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The Importance of Controlled Humidity Levels for Growing Cannabis
Ever wondered how cannabis growers get the perfect aroma? From growing cannabis to consuming it, it all comes down to humidity.
The marijuana industry is booming – generating ~$34 billion every year. As more legal growers take on the challenge, Americans are on the hunt for the best indoor grow rooms (under strict governmental rules & regulations) to obtain the best yield and improve plant growth!
Many factors need to be controlled in a grow room, such as CO2, temperature, and humidity. Controlling humidity and temperature levels is a precise science and is essential for growing cannabis, from planting the first seed to harvesting the end product.
As you probably know, all plants carry out photosynthesis, respiring CO2 from the surrounding environment via their leaves. During this process, the cannabis plant loses some water. If the air is not humid enough, the moisture content within the plant will be depleted. If this continues, the plants will lose more water than they can hold within the foliage, closing the pores in the leaves resulting in cell death.
Some people think that watering their cannabis plants will help, however, this will decrease the amount of air in the soil, causing asphyxiation to the plant and likely root rot. But, with the correct humidity levels, they will thrive!
Controlling humidity levels is not difficult, but getting it right will boost your production levels. This article will tell you everything you need to know regarding humidity, from controlling it, to what equipment you can buy.
Temperature & Relative Humidity (RH)
Humidity and temperature are closely related and play a vital role in harvesting cannabis. Humidity measures how humid the air is in a given area, in your case, this will be the grow room. Obtaining the ‘perfect’ amount of humidity (relative humidity, or RH) is crucial.
When we talk about RH, it refers to how much water air holds at a certain temperature over time. When the RH reaches over 100%, surplus water is no longer detained by air, forming water droplets as condensation occurs on the leaves. The water droplets are usually in 3 forms: fog, dew, or rain.
NOTE: During the growing process, RH should fall slowly.
Temperature is just as important as RH when growing cannabis so controlling both is essential for the best yield. It is important to note that hotter air holds more humidity than colder air. So what happens if the growing area conditions become too hot or too cold?
If temperatures are too high, especially in the flowering stage, the plant’s buds will appear fluffy. This is likely to reduce potency while the growth rate will slow down.
If the conditions inside the growing area are too cold, the cannabis plant will grow much slower. If the temperature goes near freezing (32°F) the plant will be in extreme shock, potentially fatal.
Ideal Humidity Levels for Growing Cannabis
The million-dollar question asked by many grow enthusiasts is: “What should my humidity levels be to optimize cannabis growth”.
Well, the RH level depends on the plant. Plants that originate from warmer/tropical regions thrive with high RH levels as they are well-adapted to these conditions. However, plants from colder regions prefer a less intense RH level.
Cannabis is thought to be native all around the world with Indica cannabis originating from dry mountain regions where temperatures are lower. However, with Sativa cannabis, this strain grows best and is thought to originate from much hotter, humid, subtropical regions.
Nowadays, the seeds you will find are a Sativa-Indica hybrid plant. These hybrids have emerged from heavy cross-breeding which is why most growers will assess the plants’ morphology, and run trials using different RH levels to find the best yield or end product.
Humidity Levels & Growth Stage
Depending on what stage your cannabis plants are at, will depend on how much humidity they require to grow.
There are 4 stages to cannabis growth that every grower should familiarise themselves with: seedling/clones, vegetation, early flowering, and late flowering.
- This stage involves clones or seeds from the parent cannabis plant
- Relative humidity level = high (65-70%)
- High humidity is required to establish root growth & for water uptake in the leaves
- Day temperature = 77°F
- Night temperature = ~70°F
- This stage involves the plant growing well-structured leaves
- Relative humidity level = moderate to high (40-70% depending on the strain of cannabis) – if the leaves look too wet during this stage, the humidity is too high
- During the vegetation period, the plants develop strong root systems that increase the uptake of water. You may need to reduce the humidity levels during this period
- Every week during this period, it is recommended to reduce the humidity levels by 5% and increase the temperature because, at this stage, the cannabis plant’s leaves will be absorbing and evaporating more water.
- Day temperature = 71-82°F
- Night temperature = 64-75°F
- Early Flowering
- At this stage, the cannabis plant has established a strong root system, meeting its water requirements, however, it still uses its leaves to absorb water
- Relative humidity level = low (40-50%)
- Low humidity is required to prevent mold and mildew (see below for more details on this issue)
- Day & night temperatures = 68-78°F
- Late Flowering
- This stage usually lasts 6 to 12 weeks as the cannabis plant fully matures
- Relative humidity level = low (30-40%)
- Low humidity improves the plant’s yield, taste, and overall appearance
- Day temperature = 64-75°F
- Night temperature = 60-68°F
Giving plants the correct amount of humidity, allows their pores to open up inside the leaves, respire more CO2, and grow faster. However, exposing them to too much humidity can cause diseases such as bud rot due to water build-up encouraging bacteria and fungi to overrule the foliage.
Benefits of controlling humidity include:
- Reduces bud rot from happening
- Ensures the cannabis plant will survive
- Improves potency
- Improves taste
How to Increase Humidity
- Reduce the power of your exhaust fan – this traps warm air inside the growing area
- Increase the temperature in the room
- Gently spray/mist your plants and soil to keep them moist – avoid flowering plants as this can cause the buds to rot
- Surround your plants with water (in open containers)
- Use a humidifier to trap moisture in the growing area
How to Reduce Humidity
- Increase the power of your exhaust fan – this pushed warm air outside the growing area
- Plug in a dehumidifier
- Water the plants at the start of their light period/when lights are turned on
- Increase the amount of cool air in the growing area
Keeping the humidity at the right level throughout your cannabis plant’s life cycle can be difficult, however, it is vital to monitor the plant’s growth during its 4-stage lifecycle.
At Atlas Scientific, we have a humidity sensor that not only reads relative humidity for accurate humidity monitoring, it also measures the dew point and air temperature.
Signs of Poor Humidity Levels
You hear some horror stories from cannabis growers where things have gone wrong, and this is generally from poor humidity management.
Below are a few issues that can occur, and what you can do to prevent them from happening to your stock.
White Powdery Mildew (WPM)
This fungal infection occurs in high humidity environments, which can be difficult as high humidity levels are required for the early stages of cannabis growing. When the cannabis plant is infected, it will be covered by white powder or mildew, which can be prevented if caught early on.
If you notice this taking over your plants, ensure there is ample airflow in the growing area – you can use a swinging fan.
Another fungal infection, which affects the dense cores (inner part) of the plant, making it turn white or brown with mold/rot. If you notice this on the plant’s buds, you will have to throw them away as they are now unusable.
Ensure there is enough air circulation, plenty of space between plants, and inspect the plants daily to prevent it from occurring.
Plants need nutrients to grow but give your cannabis plants too much, they will get nutrient burn, also known as nute burn. This is when the leaves turn yellow and the edges and tips turn brown looking burnt.
This process occurs when the plants take up too much water due to high temperatures and low humidity in the growing area. As they drink more water, the uptake of nutrients via their roots is excessively increased causing a nutrient burn.
When cannabis plants are young, they require higher humidity levels than mature plants (these grow best in lower humidity levels). If these requirements are not met, your cannabis plants will not reach their potential growth and optimum health.
Summing Up Humidity, Testing Equipment, and Advice
Whether it is personal or commercial use, humidity levels play a vital role in growing cannabis. By controlling relative humidity (RH) levels, you will maximize your yield and reduce issues such as white powdery mildew and bud rot.
At Atlas Scientific, we have the perfect solution to control RH levels and make growing cannabis stress-free! We understand finding the perfect humidity sensor is a mission itself, that’s why we have built our own.
Remember to check your plants daily and keep a close eye on both temperature and humidity throughout the growing process.
Hopefully, after reading this, you will be well on your way to growing healthy cannabis plants, but should you have any questions, please do not hesitate to reach out to one of our staff at Atlas Scientific, part of our world-class team.
Ideal Humidity Level for Cannabis
The humidity of your cannabis grow room plays a large part in how your plants function. It can effect the growth and final yield as well as having implications in the spread of disease and mildew. Through an understanding of exactly what your plant needs and how to make sure it has it, you will increase the quality of your grow and subsequently the marijuana you end up with. Knowledge is power!
Firstly, what is humidity? Well, humidity refers to the amount of water vapor present in the air (water vapor is simply water in its gas form). It is often referred to as a percentage, for example, a humidity of 75% means that the air currently contains 75% of the total maximum water vapor it can hold at that temperature. Also, as air increases in temperature it becomes capable of holding more water vapor, meaning temperature and humidity is related. As a result the percentage used to measure humidity is referred to as Relative Humidity (RH).
A lot of novice cultivators try to maintain a low humidity; this is a common mistake and is largely down to the idea that high humidity encourages disease amongst plants. Whilst partly true, this “play it safe” attitude can have its own adverse effects on how your cannabis plants grow.
The reason it is so important to your plants is because it will affect the rate at which they transpire. During transpiration plants release water vapor into the air, it functions along the same lines as osmosis – that the water levels inside and outside the plant will try to level out to equilibrium. This means that if you have a low humidity, your plants will rapidly transpire as water is drawn out into the air, reducing the amount of water within the plant and potentially having detrimental effects when water levels reach to low. If humidity is high then plants will transpire at a much slower rate and have a lesser potential for loss. It should be noted that cannabis plants have a “humidity” rating of pretty much 100%, so they will always transpire (which is OK as it is an essential part of its functioning).
So why do plants transpire? Well basically, they do it for a number of very important reasons. It is done for temperature control, it is how plants cool themselves and regulate their own temperature. It is also how the cannabis plants move minerals and nutrients about, as water leaves the plant it draws more up from the roots, allowing for the absorption of nutrients from the soil. Finally it is how your cannabis plants get the carbon dioxide they need out of the air – Plants open their stomata to let water vapor out, and in the process carbon dioxide gets in.
If the humidity is too low, then your cannabis plants are going to do a lot of transpiring and it will play havoc with their transportation systems. They will lose a lot of water and begin to exhibit the damage usually caused by dryness – stunted new leaves, shriveling old leaves and dying flowers.
As mentioned, whilst low humidity is usually the pitfall of most novice growers, it is for good reason – they have heard or read somewhere that high humidity is likely to cause the spread of disease, and they are not far off. High humidity has its own perils. In a grow room with excessive humidity and very little air movement (ventilation) you run the risk of exposing your plants to fungal disease, mildew and root rot. However, it is very easy to avoid, with careful grow room planning and management you should not find yourself in a situation where this happens.
The best way to monitor the RH of your grow room is to use a hygrometer, this should give you an accurate read out of the exact water vapor content of the air.
Humidity effect cannabis plants throughout their entire life cycle, below explains how it affects them at each stage and what the optimal humidity is.
At this stage the ideal RH is 70-80%. This RH will ensure that the seedlings do not put too much of their energy into their transpiration process, as there is not much of an imbalance. This will allow your seedling to focus their energy into root and leaf growth. Your little ones will also need to maintain some level of transpiration in order to draw up nutrients from the growing medium.
A great way to control the humidity of you grow room is with good ventilation, and the use of a humidifier when humidity are beginning to get a bit low. A humidifier is an easy to obtain, cheap bit of equipment that simply introduces more water vapor into the air. When used in conjunction with a hygrometer you should easily be able to keep RH within your cannabis plants’ safe limit.
In this stage the RH can be 50-80%. Now that your plants have entered their main growing phase the RH can be a lot more varied. This is because your plant will now have a much bigger surface area with which to transpire, meaning less stress is put on it through faster transpiration.
However, this does mean your plants can transpire at a much greater rate, be sure to keep an eye on your plants. If the levels of humidity drops below a safe level then your plants will transpire so rapidly that they run the risk of over fertilization from their fast uptake of nutrients drawn in from the soil.
Once your cannabis is flowering you will want to consider dropping the RH greatly. This is in order to reduce the risk of the dreaded rot. You ideally want you grow room to have a relative humidity of 40-50% now.
Keeping track and controlling your grow rooms humidity is important if you want to really get the most out of your plants. It is another important factor that is usually overlooked by less experienced cultivators. Now that you have a better understanding of its impact you should be able to utilize the knowledge to improve the quality of your grow.