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Resolving Common Grow Room Humidity Issues: A Detailed Guide 2023

Controlling the humidity in your cannabis grow room is more than just a prerequisite—it's a science. Understanding and managing grow room humidity is fundamental to successful cannabis cultivation. As plants mature, their requirements change, making it a challenge to maintain optimal conditions in your grow room. With too much humidity, your plants become susceptible to mold; with too little, they may suffer dehydration.

This comprehensive guide takes you through the ins and outs of resolving common grow room humidity issues. From the basics to the common challenges and their respective solutions, we will empower you with the knowledge to ensure your cannabis plants thrive in just the right conditions.

Whether you're an experienced grower or just starting, the following content will provide invaluable insights to overcome over-humidity and under-humidity issues.

So, let's dive into the world of cannabis cultivation humidity control. Your optimal harvest awaits.

Grow Room Humidity Basics for Cannabis Cultivation

Before diving into the solution, let's start by unpacking some definitions related to humidity.

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Absolute Humidity

   It's the actual air moisture volume measured in grams per cubic meter.

Relative Humidity

It's the ratio of the current moisture in the air to the maximum moisture the air could potentially hold at a specific temperature.

Specific Humidity

This one is also called the humidity ratio and compares the weight of the water vapor and that of dry air.

Why Grow Room Humidity Matters in Cannabis Cultivation

When controlled effectively, humidity can be a key to success in cannabis cultivation. It can promote healthier plants, faster growth, and higher yields. However, achieving this balance requires careful monitoring as both high and low levels can create issues.

So, let's take a closer look at how both excess and deficient humidity conditions can impact cannabis growth if not addressed promptly.

Impact of Over-Humidity on Cannabis Growth

Excessive humidity can result in several issues:

  1. Mold and Fungus Development: High humidity levels create the perfect conditions for mold, mildew, and fungus, damaging the cannabis plant and ruining its harvest.
  2. Stunted Growth: Over-humidity slows down the plant's transpiration rate, limiting nutrient uptake, stunting growth, and ultimately leading to lower yields.
  3. Pests Infestations: Pests, such as spider mites and fungus gnats, are more likely to infest cannabis plants in an over-humid environment.

Impact of Under-Humidity on Cannabis Growth

Conversely, under-humidity can lead to its own set of complications:

  1. Dehydration: With low humidity, plants lose water quickly, leading to wilting or drooping leaves.
  2. Nutrient Burn: Rapid water loss can cause an over-concentration of nutrients in the plant, resulting in nutrient burn.
  3. Slow Growth: As with over-humidity, under-humidity can also stunt the plant's growth, as it struggles to maintain hydration.

Recognizing the Signs of Humidity Issues in Your Plants

Identifying symptoms of humidity imbalance in your plants early can save you from catastrophic loss:

  • Over-Humidity Signs: Slow growth, persistent dampness in the grow room, mold or mildew on plants or equipment, frequent pest infestations.
  • Under-Humidity Signs: Wilting or drooping leaves, curling or yellowing of leaves, nutrient burn signs such as brown spots or 'burnt' leaf tips, plants needing frequent watering.

By monitoring these symptoms and adjusting humidity levels accordingly, you can safeguard your cannabis crops from potential damage and optimize their growth conditions.

The Connection Between Temperature and Grow Room Humidity

Temperature and humidity: two key players in the world of cannabis cultivation, each capable of impacting your plant's health and potential yield. These variables are far from independent; their interplay is paramount in your grow room.

As temperature increases, the air's capacity to hold moisture also rises. When temperatures fall, the air's moisture-holding capacity decreases, causing changes in humidity levels. But it's a delicate balance. High temperature coupled with high humidity can foster unwanted mold or mildew, whereas low temperature with low humidity can dehydrate your plants, stunting their growth.

Diving deeper, we encounter Vapor Pressure Deficit (VPD). VPD describes how temperature and humidity interact to impact plant transpiration. Achieving the optimal VPD encourages plant health and robust growth. Remember, different growth stages of cannabis plants may require different VPDs.

To give you a clear picture, let's take a look at the following chart which outlines the ideal VPD for different stages of cannabis growth.


Factors Influencing Grow Room Humidity in Cannabis Cultivation

Managing the humidity in a cannabis grow room depends on a complex interplay of multiple elements. Let's take a closer look at these contributing factors.

The Impact of Grow Room Size and Design on Humidity

Your grow room's size and layout aren't just about fitting your plants - they also influence your control over humidity.

Larger rooms take longer to become overly humid than smaller ones, which can quickly become too humid.

The design features of your grow room, such as ceiling height, insulation, and material choices, can also affect your grow space's humidity dynamics. A carefully thought-out grow room design makes humidity control more manageable.

The Role of Plants in Modulating Humidity

Your plants don't just experience the room's humidity - they contribute to it. Through transpiration - plants releasing water into the environment - they can increase the room's overall humidity levels.

As your plants grow and their leaf surface area expands, the amount of water they release and, thus, the room's humidity may increase.

Ventilation and Airflow in the Grow Room

Ventilation and airflow aren't just about keeping your plants oxygenated but also about humidity control. A well-designed ventilation system can maintain an even temperature and balance your room's humidity.

Consistent airflow distributes temperature and humidity evenly across your grow room, supporting ideal plant transpiration rates and warding off mold and pests. However, too much airflow can stress your plants, making it crucial to find the right balance.


Colder regions have less moisture in the air due to the temperature relationship mentioned earlier. Therefore, when growing cannabis in such areas, increasing the relative humidity to an optimal level is essential.

In contrast, hot or tropical regions generally require less humidity control. Because many cannabis plants thrive in relatively higher humidity levels.


Over time, numerous cannabis varieties have been developed. Some cannabis species are better suited to warmer, more humid environments. But others are adapted to colder, less humid conditions.

Other Environmental Factors

Moving beyond the previously discussed factors, we should not overlook other vital elements influencing humidity in the cannabis cultivation environment.

  • Lighting: Various grow lights produce different heat levels, affecting room humidity. For instance, HID lights create more heat than LED lights, possibly raising humidity.
  • Plant Density: The number of plants in a space impacts humidity. More plants lead to higher transpiration and humidity levels.
  • Watering Practices: Overwatering or poor irrigation can cause high humidity. Careful watering and using moisture meters help maintain the right humidity levels.

Equally important to these factors is the stage of growth of the cannabis plant, which carries its own unique influence on humidity requirements. Next, we will delve into the humidity needs at different growth stages of cannabis.

Ideal Grow Room Humidity Levels for Different Cannabis Growth Stages

Just like humans, cannabis plants have different needs at different stages of life. In the case of cannabis, these needs even extend to preferred humidity levels.

Seedling Stage

In the seedling stage, cannabis plants are just beginning their journey to maturity. To support their development, they require a specific set of conditions:

  • Humidity levels: Seedlings and clones thrive in high humidity levels of 65-70%. High humidity reduces transpiration through the leaves, easing the burden on their developing root systems.
  • Temperatures: With lights on, the temperature should be between 68–77°F. When the lights are off, temperatures should be 8-9°F lower.
pc-altaqua grow room humidity-grow room humidity and temperature-seedling stage

Why these conditions? At this stage, cannabis plants are developing their root systems and absorbing water primarily through their leaves. By maintaining high humidity and the appropriate temperature range, we can help the seedlings to establish their root systems without undue stress.

If you're growing seedlings in a room with mature plants, consider using humidity domes. These domes help maintain the high humidity levels that seedlings love. Just make sure the domes are properly ventilated to prevent excessive moisture build-up and to ensure adequate CO2 exchange.

Vegetative Stage

As your cannabis plants transition into the vegetative stage, their humidity and temperature need to change. It's time to tweak the conditions in your grow room accordingly:

  • Humidity levels: You should gradually reduce humidity by about 5% each week, keeping it within a 40-70% range. This change helps prepare your cannabis plants for their eventual transition to the flowering stage.
  • Temperatures: During the vegetative stage, maintain temperatures between 71-82°F when the lights are on and 7-8°F lower when the lights are off.
pc-altaqua grow room humidity-grow room humidity and temperature-vegetative stage

The rationale behind these changes lies in the development of your plants. By now, the root systems are more mature and capable of absorbing most of the necessary water. The evaporation from the leaves now serves to cool the plants. Reducing the humidity level in increments allows the plants to adapt and further expand their root systems while focusing on leafy growth and stem elongation.

Remember not to drop the humidity below 40%, as this could stress the plants and hinder their growth. Just like in the seedling stage, ensure that your environment adapts to the changing needs of your cannabis plants for optimal growth.

Early Flowering Stage

As the cannabis plants blossom into the early flowering stage, your attention should now turn towards preventing mold and mildew while promoting resinous bud growth:

  • Humidity levels: It's recommended to lower the humidity to 40-50%. Be vigilant and ensure it doesn't exceed 60% to prevent the onset of mold and mildew.
  • Temperatures: Maintain temperatures within 68-79°F when the lights are on and 8-9°F lower when they're off. High temperatures above 84°F should be strictly avoided as they can quickly dehydrate your plants and stress them, adversely affecting yield.
pc-altaqua grow room humidity-grow room humidity and temperature-flowering stage

The shift to a lower humidity environment during this stage is crucial in staving off mold and mildew. Accommodating these changes with cooler temperatures will also help maintain an optimal VPD (Vapor Pressure Deficit) for your cannabis plants. These conditions create an environment conducive to bud production and overall plant health.

Be mindful of the temperature limits, as high heat coupled with low humidity can lead to dehydration and stress in your plants, which is detrimental to your final yield.

Late Flowering Stage

As your cannabis plants transition into the late flowering stage, the environmental conditions must be adjusted to facilitate the maturation of the dense, resinous buds you've been diligently working towards:

  • Humidity levels: Further decrease humidity to 35-50%. This reduction is pivotal to deter mold formation while the buds develop and become denser.
  • Temperatures: Aim for temperatures in the range of 64-75°F when the lights are on and around 8°F lower when they're off.
pc-altaqua grow room humidity-grow room humidity and temperature-late flowering stage

During the late flowering stage, your plants are in their final push to produce the aromatic, resin-rich buds that are the hallmark of quality cannabis. Lower humidity levels are necessary to prevent molds that could threaten your crop in this critical phase. These conditions and appropriate temperature control will pave the way for your cannabis plants to yield the bountiful harvest you've been nurturing them for.

Post-Harvest Humidity Control: Curing and Processing

Humidity control doesn't stop after harvest - it's crucial during the curing and processing stages as well.

The Role of Humidity in Curing Cannabis

Once your cannabis has been harvested, the curing process begins, a phase just as critical as the growing stages. This is where your control of humidity becomes key once again:

Humidity levels: Aim for a 45-60% range. This balanced humidity level ensures your buds dry out gradually, preserving their quality and preventing them from becoming brittle and harsh.

Temperatures: Keep the temperatures between 60-72°F. Lower temperatures aid in a slow, even drying process, which is ideal for preserving the flavorful terpenes in your buds.

Curing cannabis is an art form in itself. The right humidity and temperature settings can make the difference between a successful harvest and a subpar one. It's about finding the right balance - too dry, and the buds become brittle; too damp, and you risk mold formation.

pc-altaqua grow room humidity-grow room humidity and temp chart

Maintaining Optimal Humidity During Cannabis Processing

Even after harvesting and curing, it's essential to maintain optimal humidity control during the processing and storage of your cannabis:

Humidity levels: Try to maintain a steady humidity level of around 59-65%. This prevents the buds from drying out too quickly, preserving their potency and freshness.

Temperatures: Stick to temperatures around 60-72°F. High temperatures can damage terpenes and cause rapid drying, which can degrade the quality of your cannabis.

In the processing stage, the climate control principles you've learned during cultivation still apply. Humidity and temperature control continue to be crucial factors in preserving the quality of your cannabis. By maintaining these conditions, you're ensuring that your cannabis stays fresh, potent, and ready for your clients to enjoy.

How to Monitor Grow Room Humidity

Now, let's focus on how to track and adjust the humidity in your grow room consistently, a key aspect of maximizing the yield and quality of your cannabis crops.

Essential Tools for Monitoring Grow Room Humidity

Choosing the right tools for tracking and managing your grow room's humidity can make a world of difference in your cultivation journey.

Understanding the Different Types of Hygrometers

A hygrometer, your go-to instrument for measuring humidity, comes in different types, each with its strengths and weaknesses. Here's a quick comparison:

Why Use a Digital Thermometer-Hygrometer

A digital thermometer-hygrometer is a powerful tool that allows you to monitor both temperature and humidity in one go. Considering these two factors are interlinked and crucial to your cannabis growth, having a device that tracks both can make your cultivation process more streamlined and efficient.

Interpreting Humidity Readings in Your Cannabis Grow Room

Merely knowing the humidity level isn't enough; understanding its impact on your plants and making informed decisions is the real game-changer.

Reading Humidity Levels Accurately

The relative humidity is expressed as a percentage, so an accurate reading from your hygrometer is vital. You'll need to compare these readings against the ideal levels for your current growth stage and adjust your humidity control measures accordingly.

Understanding the Meaning of Humidity Fluctuations

Changes in humidity can be a warning sign of potential problems. A sudden spike may indicate a water leak, while a rapid drop might mean your dehumidifier is overworking. Recognizing these fluctuations and their potential causes can help you preemptively address issues, saving your plants from unnecessary stress.

How to Make Adjustments Based on Humidity Readings

Armed with an understanding of your humidity readings and what they mean for your plants, you can make the necessary adjustments to your grow room.

These changes might involve tweaking your HVAC settings, deploying dehumidifiers or humidifiers, adjusting irrigation schedules, or even introducing plant-friendly humidity-absorbing materials into your grow room. This proactive, data-informed approach will ensure your plants flourish in the best conditions possible.

How to Control Grow Room Humidity

Successful cannabis cultivation requires diligent attention to your grow room's humidity. Let's explore how to resolve both high and low humidity issues.

How to Resolve Low Grow Room Humidity Problems

If your grow room's air is too dry, there are several strategies you can adopt to increase humidity:

Utilizing Humidifiers for Maintaining Grow Room Humidity

Just as dehumidifiers extract moisture, humidifiers add it. But remember, moderation is key. Even if your grow room's air is dry, over-humidifying can swing the pendulum too far in the other direction, leading to the issues associated with high humidity. Therefore, select a humidifier with a built-in humidistat to maintain a balanced environment.

Plant Spacing and Canopy Management

Crowded grow rooms aren't just unsightly; they're also humidity traps. When plants are placed too closely, they hinder air circulation, leading to a damp microclimate ripe for mold and other fungal infections. So, make sure there's enough space between your plants to allow air movement.

Canopy management is another effective strategy. Regularly trimming and pruning your plants allows light and air to penetrate through the leaves and branches, reducing the chance of humidity accumulation.

Manipulating Plant Transpiration to Increase Humidity

Plants aren't just passive recipients of care; they're active participants in their environment. Through transpiration, plants release moisture, thereby naturally increasing the room's humidity. So, if your grow room has space for a few more plants, consider adding them to help boost humidity. Larger plants tend to transpire more, so they can be particularly helpful in this regard.

Employing Water Features to Boost Humidity

Incorporating water features in your grow room can also help increase humidity. For example, a tray of water placed inside the grow room can enhance humidity through evaporation. Place it near the intake vent for better moisture distribution across the room. Just be cautious to avoid standing water for prolonged periods as it can become a breeding ground for unwanted pests or pathogens.

This technique can be especially useful in smaller grow rooms where investing in a humidifier might be unnecessary.

How to Resolve High Grow Room Humidity Problems

On the other hand, high humidity in your cannabis grow room isn't a hopeless situation. Here are a few methods you can employ to bring your moisture levels back down to the sweet spot:

Optimizing Ventilation and Airflow

Taming high humidity starts with boosting airflow. Enhanced ventilation halts moisture build-up, ensuring your grow room breathes in fresh, dry air. Equip your space with inline and oscillating fans, or even an air conditioner. The key? Strategic placement to maximize their breeze-sweeping power and maintain a dry haven for your plants.

Don't skimp on installing sturdy exhaust fans, either. They're your ticket to pushing out hot, damp air and inviting cool, fresh air in through purposeful vents. And if you've got an air conditioner, maintenance is a must. Clogged filters can jam your airflow and crank up humidity. Stay ahead with regular cleaning and you'll keep the airflow smooth and humidity in control.

Timely and Proper Irrigation

Wise watering can throw a punch at humidity woes. Overdoing the water not only opens the door to root rot but also cranks up the humidity dial. So, keep a keen eye on your plants' water needs, and always have a way for the surplus to drain off.

Exploring Heat Control

Raising the temperature notch by notch could be your secret weapon since warmer air can retain more moisture. But, don't let the heat off the leash. Like us, plants have their temperature comfort zones, and overheating could set off a domino effect of other issues.

Deploying Dehumidifiers to Reduce Excess Moisture

Dehumidifiers can be your last resort when all else fails. For smaller, entry-level grow rooms, basic dehumidifiers can come in handy. They act as moisture magnets, pulling extra water out of the air.

However, for larger, high-end grow rooms, HVAC (Heating, Ventilation, and Air Conditioning) systems might be a better fit. They are not just about heat control, they also balance humidity, providing a full-circle solution to your grow room climate needs.

Dealing with humidity issues may feel overwhelming, but with the right tools and strategies, you can create the ideal growing conditions for your cannabis plants.

HVAC System's Advantages in Controlling Temperature and Humidity

While numerous tactics to control humidity in grow rooms hold their merit, a shift towards more efficient, comprehensive solutions is discernible in today's advanced cultivation practices. That's where HVAC (Heating, Ventilation, and Air Conditioning) systems come into play, excelling in their ability to regulate both temperature and humidity with finesse.

Let's unpack the unique advantages HVAC systems bring to the table in terms of maintaining perfect climatic conditions within your grow rooms. When we talk about HVAC systems in the context of indoor cultivation, a few names resonate with industry expertise. QUEST and Surna are two such frontrunners that have proven their mettle, widely recognized for their superior-quality HVAC solutions.

However, when balancing high performance and affordability, another contender stands out—Altaqua. A relatively new yet rapidly growing player, Altaqua offers cost-effective HVAC solutions that don’t compromise on functionality, making it an increasingly popular choice amongst cannabis cultivators. Let's dive deeper into what sets Altaqua apart.

HVAC Systems for Large-Scale Grow Rooms

Running a large-scale grow room? Standalone dehumidifiers and fans may no longer suffice. You need a powerhouse that's built to cater to the demands of commercial operations. That's where Altaqua's HVAC systems prove their mettle.

These systems amalgamate heating, cooling, and ventilation into one single, efficient package. Unlike smaller, discrete devices, Altaqua's HVAC solutions can handle larger spaces with finesse, ensuring uniform climate control across your vast grow room.

Precision Control with HVAC Systems

Altaqua's HVAC systems offer precision, a factor that's crucial for maintaining optimal growing conditions. These systems let you fine-tune temperature and humidity levels to perfection. With Altaqua, say goodbye to erratic climate fluctuations and hello to consistent, trustworthy control.

Altaqua's HVAC systems come equipped with smart controllers or programmable thermostats. These tools allow you to set precise conditions for various growth stages or times of the day, basically putting your climate control on autopilot.

Balancing Cost and Efficiency with HVAC Systems

Investing in an HVAC system can feel hefty at first glance. But consider this: they’re not just a purchase, but a long-term investment. In the cost-efficiency department, Altaqua's HVAC systems earn their stripes.

By keeping your grow environment in the sweet spot, these systems promote healthier crops and bolster yields, directly enhancing your bottom line. Moreover, compared to using a medley of standalone devices, Altaqua's HVAC systems consume less power and offer energy-saving modes and programmable schedules, resulting in trimmed down utility bills.

The cost benefits don't stop there. Altaqua's HVAC systems also help dodge costly disasters like bud rot or mold growth. This not only saves you the expenses for damage control but also spares you the cost and hassle of plant replacement. In essence, Altaqua offers a cost-effective route to climate control without compromising quality.

Maintenance and Daily Management of Cannabis Grow Room Humidity

Ensuring optimal humidity for your cannabis plants doesn't end with installing the necessary equipment. It requires ongoing attention and maintenance to keep things running smoothly and your plants thriving.

Routine Checks for Grow Room Humidity Levels

Just like how you regularly check your plants for health signs, the humidity levels in your grow room need frequent monitoring too. Keep an eye on your HVAC or humidity control system's digital readouts, and calibrate them periodically to ensure their accuracy. Regular checks allow you to make timely adjustments if the humidity level deviates from the ideal range.

Long-Term Maintenance Tips for Humidity Control Equipment

To keep your humidity control equipment in prime condition, adopt a routine maintenance schedule. Regularly clean and replace filters, check for leaks, and ensure all components are functioning as they should.

For Altaqua HVAC systems, refer to your user manual or consult with Altaqua's expert support team for the best maintenance practices.

Conclusion: Mastering Grow Room Humidity in Your Cannabis Cultivation Journey

Mastering grow room humidity is crucial for successful cannabis cultivation. It impacts plant health, growth rate, and final yield. We've discussed the implications of both high and low humidity, different solutions to manage humidity, and the advanced control you can achieve with HVAC systems, particularly those from Altaqua.

If you need help with your HVAC system or any other aspect of humidity control, don't hesitate to reach out to Altaqua. With extensive expertise in advanced climate control solutions, Altaqua can assist you in achieving an optimal grow room environment.


1.What are the ideal grow room humidity levels for different cannabis growth stages?

Ideal humidity varies with each stage of growth. For seedlings, keep humidity around 65-70%. For the vegetative stage, 40%-70% is ideal. During the early flowering stage, aim for 40%-50%, and in the late flowering stage, maintain around 35%-50%.

2.How can I effectively monitor my grow room's humidity?

Tools like hygrometers, humidity controllers, HVAC systems, and digital thermometer-hygrometers are essential for monitoring humidity levels. Regularly check these tools and interpret the readings to make necessary adjustments.

3.What impacts could over-humidity and under-humidity have on my cannabis plants?

Over-humidity can lead to mold, mildew, and other moisture-loving problems, while under-humidity can cause slow growth, yellowing leaves, and diminished yield.

4.How can I resolve high or low grow room humidity problems?

For high humidity, invest in a quality dehumidifier, improve ventilation, and manage your plant canopy effectively. For low humidity, use humidifiers, manipulate plant transpiration, and employ water features to increase humidity levels.

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