Does Humidity Rise or Fall: A Comprehensive Guide for Plant Growth

A houseplant's health significantly depends on the puzzling question, "does humidity rise or fall?" As indoor growers, it's crucial to comprehend why humidity levels are prone to fluctuation.

In this article, we'll delve into the conditions that make humidity rise or fall and how these fluctuations impact your plants. Armed with this knowledge, you'll learn how to maintain optimal humidity levels for your indoor plants, ensuring their health and growth.

Understanding "does humidity rise or fall" is the key to unlocking the full potential of your indoor gardening efforts.

What is humidity, and why is it essential for indoor growing

The term humidity refers to the amount of moisture in the air. A plant's ability to transpire or release water is affected by humidity when growing indoors. Low humidity will cause plants to dehydrate and wilt. A high humidity will cause mold and other fungal diseases. Proper humidity levels are essential to plant growth.

Temperature, ventilation, and watering time affect humidity in the grow room. Lighting equipment can raise temperatures, but turning them off can drop them and cause moisture to accumulate.

The humidity level should be around 65~70% during the seedling/clone stage. Germination should be in a humid environment of 40~70% and gradual reduction to 55~60% before flowering. When flowering, the humidity should be 40~50%, and when harvesting, 45~60%. A humidifier increases humidity, while a dehumidifier decreases it.

And the latest technology, the grow room hvac system, can automatically control well the humidity with suitable temperature together.

Relatively speaking, why is humidity a problem

A greenhouse or grow room's humidity fluctuates constantly, making it difficult to maintain the right level. Understanding relative humidity (RH) is fundamental. RH represents the ratio between moisture in the air and the maximum amount of water air can hold at a given temperature. Air temperature changes affect humidity levels, so they must be monitored.

Humidity levels vary with temperature in indoor grow rooms. 'Relative' refers to how much water air can hold at different temperatures. High temperatures allow the stand to hold more water, resulting in higher humidity. Lower temperatures result in less moisture in the air, resulting in lower humidity. It's essential to maintain a consistent temperature and humidity level in your grow room.

Plant development determines the optimal humidity level. A humidity level of 40 to 70% is recommended during plant growth. For mold and mildew prevention, reduce humidity levels to 40~50% during flowering. Humidity levels are affected by temperature, with warmer air carrying more moisture. Therefore, monitoring the temperature and humidity is essential to ensure optimal growing conditions. Using the Altaqua grow room HVAC system is the perfect solution.

Indoor grow rooms must maintain proper humidity levels. In high humidity, plants have difficulty cooling themselves through transpiration. Water cannot evaporate from leaves when the air is too humid, reducing nutrient uptake. Too much humidity can alos multiply mold spores and damage crops.

Powdery mildew and botrytis are common pathogens that can quickly spread and cause bud rot, resulting in reduced crop yields.

does humidity rise or fall

How does humidity affect plant growth and health

Plants depend on humidity for growth and health. Stunted growth occurs when humidity levels are too low. Plants may lose water faster than they can absorb moisture from the soil. Alternatively, too much humidity can lead to mold and other fungal diseases. Moisture encourages fungi growth.

Factors Affecting Humidity Levels in a Growth Chamber

Various factors can affect humidity levels in growing rooms. A key factor is temperature. As temperature rises, moisture concentration in the air increases. Likewise, humidity levels will decrease as the temperature decreases.

Other factors affecting humidity levels include:

  • The size of the grow room.
  • The number of plants produced.
  • The type of ventilation system used.

How to Control Growth Room Humidity

Maintain Proper Humidity Levels in Your Indoor Grow Room

When it comes to maintaining ideal humidity levels in your indoor grow room, improving your irrigation methods is essential. This means ensuring that all the nutrient solutions go directly to the roots without any excess loss.

Regardless of the specific growing medium or technique used, the key to reducing moisture in the air is to introduce less water throughout the growth chamber. By taking these steps, growers can help prevent excessive humidity and create the optimal environment for plants to thrive.

measure humidity

Controlling humidity starts with measuring it accurately. Moisture meters can give pretty accurate readings, but more expensive psychrometers are the best option for precise information for severe growers. By knowing and monitoring humidity levels, growers can make adjustments to ensure optimal plant growth conditions.

Installing a humidistat is essential when maintaining the humidity levels in your indoor grow room. Unlike a thermostat, it controls humidity. It will activate the ventilation system when the humidity level rises too high.

In many cases, proper ventilation and the heat generated by grow lights are sufficient to regulate the humidity levels in the grow room.

Strategies for controlling humidity levels in the growth chamber

Indoor growers can use various strategies to control humidity levels.

A dehumidifier can effectively remove excess moisture. Keeping the plants clean is especially important during flowering when mold is more likely to occur.

Another strategy is to use ventilation fans to circulate air and prevent stagnant moisture pockets from forming. Growers can also use a moisture meter to monitor and adjust levels. Finally, choosing the right plant strain for the environment can help maintain optimal humidity levels.

A grow room's temperature can also control humidity levels. Increase the temperature for more moisture, or decrease the temperature for less moisture.

What humidity level should you maintain

A successful indoor grow room requires the right temperature and humidity levels, which depend on factors such as strain, stage, and pressure applied. Cannabis strains require different levels of humidity. Alfalfa and alfalfa-dominant strains originating thrive at high humidity levels. 

Indica varieties from the inland areas, on the other hand, prefer slightly drier conditions. Optimal growth and yield require constant monitoring and adjustment of humidity levels.

As the intake and exhaust force change, humidity levels in indoor grow rooms can either rise or fall. As a result of this stress, the leaves' stomata are also affected, ultimately affecting the exchange of air and the growth of the plant.

Therefore, many growers control the pressure and carbon dioxide levels in the grow chamber to optimize growth.

The importance of monitoring and adjusting humidity levels for optimal plant growth

Indoor plant growth and development are influenced by humidity levels. In low humidity, plants can wilt, while in high humidity, mold and mildew can grow. Maintaining optimal humidity levels is key to plant growth.

Different tools and strategies can be used to accomplish this, such as grow room hvac systems, dehumidifiers, ventilation fans, and hygrometers. Maintaining the right humidity levels can aachieve high-quality yields and help their plants thrive.


Growth and health of plants are heavily dependent on humidity levels. Humidity levels between 40~60% are recommended for plant growth. With a dehumidifier, you can remove excess moisture. The cooling elements in a dehumidifier condense water. A heating element retains heat after air passes over it. Using this process, we can regulate humidity levels and create a healthy environment for plants.

Humidity levels can be crucial to the success of indoor grow rooms. High humidity can lead to mold and mildew growth, while low humidity can cause plants to dry out. Dehumidifiers help growers regulate moisture levels in the air. These devices are portable or wall mounted and come in different sizes. Some dehumidifiers offer air filtration to reduce mold and mildew risk. Moreover, unlike air conditioners, they won't increase heating needs.

As humidity is closely related to temperature, maintaining a proper level in an indoor grow room can be challenging. Therefore, humidity levels can fluctuate and cause frustration, but by monitoring your plants and using the right equipment, you can achieve optimal growing conditions.

In indoor grow rooms, humidity levels can be controlled through cooling and heating. Complex methods have both advantages and disadvantages.

In a closed-loop chilled water system, humidity levels can be controlled by passing the air in the grow chamber through conductive coils filled with cold or hot water. This process transfers heat between the waves and the atmosphere, helping to regulate humidity levels. While this method is energy efficient and precise, it is also more expensive and requires a skilled installer to avoid leaks and other potential problems.

And choosing the type of HVAC system can play an essential role in controlling the humidity level. This HVAC system can achieve the dual purpose of precisely controlling temperature and humidity simultaneously and is easy to install. The indoor and outdoor units only need to be connected through copper pipes. For more information, you are welcome to contact us to provide you with a plan.

Controls and Automation

It may be worth investing in a conditioning system that can communicate with other equipment and make adjustments as needed to maintain a consistent humidity level. While these systems may be more complex, they can create a more cohesive and energy-efficient climate solution for your grow room.

Our HVAC has ModBus-compliant systems allowing centralized control via a software interface. By monitoring and adjusting temperature, humidity, CO2, ventilation, and lighting, growers can ensure optimal plant growth. Moisture levels can rise or fall depending on ventilation, temperature, and the stage of plant growth, so be vigilant.

At Altaqua, we offer various products and services to help growers manage their climates effectively. Contact us today to learn more.


1. Is humidity higher at ceiling or floor?

Humidity is generally higher near the floor due to cooler temperatures and condensation.

2. Is humidity higher upstairs or downstairs?

Humidity can be higher downstairs as warm, moist air tends to rise and then cool and condense in cooler areas.

3. How does humidity disperse in a room?

Humidity disperses in a room through air movement. It can vary due to temperature differences, airflow, and the presence of water sources.

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