Everything you need to know about growing cannabis at home

How to Manage Humidity when Growing Cannabis Plants

by | Jun 6, 2022 | Cannabis, Environmental Threats, Getting Started, Troubleshooting

Humidity is a tricky thing to manage, especially in the world of cannabis cultivation. Cannabis humidity levels can be affected by outdoor humidity, humidity caused by overwatering, humidity caused by under-watering, and many other factors. If you’re not careful about managing your humidity levels it can lead to mold or fungus problems that will destroy your plants. This article outlines how you can maintain proper humidity for the different stages of cannabis plant growth as well as what happens if you have too much or too little humidity and how to prevent humidity problems overall for indoor growers with marijuana plants.

What is humidity?

Humidity is the amount of water vapor in the air. The humidity level, or humidity percentage, tells you how much moisture content there is in the air relative to what would be present if it were saturated at 100%. Humidity can be defined as high humidity if there is a lot of water vapor in the air and low humidity if there just isn’t that much moisture.

What is the difference between humidity and relative humidity?

Relative humidity tells you how moist the air actually feels to your skin. It’s usually given as a percentage, with 100% being completely saturated at whatever temperature it happens to be at. Relative humidity is a measure of the current humidity level as compared with what it feels like when saturated. It can help growers determine whether their plants are getting too wet or not enough.

For example, if your humidity is 100% and the temperature is 70°F (21°C), then the air actually feels like it has a higher temperature to you than if the humidity was at 30%. If you take two identical plants in two different rooms where one room’s humidity was 90% and another’s 40%, even though both are completely saturated, the humidity in the second room will feel like it’s much lower to your skin.

Why does my cannabis plant need proper humidity?

The cannabis plants you grow indoors require humidity for all stages of their growth cycle to maintain plant health; however, humidity requirements change during different parts of marijuana flowering and growing stages.

During the vegetative stage, which is the stage after being a seedling but before flowering, high humidity levels are beneficial for humidity regulation and to help stimulate vegetative growth. Humidity helps the plant grow strong, lush stems and leaves.

During the flowering stage, which is the final stage before harvest when your plant is growing buds, humidity plays an important role in the reproductive process of cannabis plants, as humidity is a major player in pollination. But when it comes time to harvest your weed, you should dry out all trichomes prior to curing them if you want high THC content in your finished product.

What is the ideal humidity for the different stages of cannabis plant growth?

The optimal humidity for cannabis plants will vary during the different stages of growth.

When your plant is germinating or a seedling, the relative humidity (RH) levels should be around 80%.

During vegetation, humidity can range anywhere between 40-70% relative humidity (RH) with 50% RH being optimal to make sure plants get enough moisture without getting too wet or damp; however, during flowering humidity levels should be maintained around 50% RH for the first half of flowering and then gradually decreased to 40-50% RH as your buds begin to develop.

This humidity level should be maintained until harvest time when humidity levels can return back down to around 30-40%. These are our ideal conditions for the perfect level of moisture throughout your indoor grow, however, there are many different methods available for cannabis growers and others may use different measurements for their optimal range.

What happens if my cannabis plant has too much humidity?

If humidity is too high during vegetation humidity can lead to humidity problems. These problems can lead to humidity toxicity, humidity burn, and damage to the plant roots with root rot. In other words, too much humidity for your vegetation-stage cannabis plants can lead to lots of problems as it interferes with the plant’s ability to absorb essential nutrients from its growing medium which can affect growth rates but doesn’t improve quality or yield. If you give a young plant high humidity levels during vegetative growth, humidity can cause you to get bigger and taller plants that lack the essential lateral branching needed for good yields.

If humidity is too high during flowering humidity it will also cause your plants to become susceptible to bud mold or fungus, which can ruin an entire crop in a couple of days if not caught early on.

What happens if my cannabis plant does not have enough humidity?

But too much humidity is not always a bad thing; it’s actually possible for humidity levels to be too low during vegetation which means your plant may stretch more than necessary due to low humidity levels. If the humidity levels are too low for vegetation they may lead to humidity stress. When a plant suffers humidity stress it can lead to nutrient deficiency, slow growth rates, and humidity burn. In other words, if humidity levels are too low for your cannabis plants during vegetation it leads to a whole host of problems that you definitely don’t want.

How can I prevent humidity problems when growing cannabis plants?

There are many different steps you can take to help control your humidity issues such as humidity control fans, humidifiers, and dehumidifiers. If humidity levels get too high during the vegetation stage it’s best to use a humidity-controlled fan or multiple humidity-controlled fans if necessary, but make sure you keep an eye on humidity levels; otherwise, your plants can dry out quickly.

Dehumidifiers also work well during any stage to reduce humidity levels and prevent bud mold or fungus from forming on your plants.
If humidity levels remain low during the vegetation stage, humidity control humidifiers can be a great option to control humidity for indoor cannabis growers. Other ways to raise humidity levels include humidity trays, humidity domes, humidity monitors, and humidity control foggers.

Airflow also plays a crucial role in preventing humidity problems by creating air movement through your grow space. This creates an updraft that prevents humidity from accumulating at the top of your growing area, thus preventing humidity problems and humidity-related issues like bud mold or fungus.


No matter where you live humidity will always be the same amount of water vapor in the air…right? Well, not exactly!

When it comes to growing cannabis humidity can mean everything or nothing at all depending on how much humidity there actually is and what type of humidity we’re talking about. Humidity is the amount of moisture in the air while relative humidity is a percentage of the moisture in the air compared to if that same air had the maximum amount of moisture. Humidity is needed to help grow healthy plants, although it should be at different levels during the different stages of plant growth.

If your plant has too much or too little humidity it will lead to various problems. However, having excess moisture in humid conditions during flower is a great way to promote mold and fungal problems. Ensuring your plant has enough airflow is beneficial to preventing humidity problems and using humidity monitors and controls will also help regulate it.

Should you have any further questions, please refer to our other articles about mold, bud rot, and vapor pressure deficit, also known as VPD.

To learn more about growing cannabis at home consider checking out our guides on: Getting Started, Troubleshooting, and Optimizing your Grow or search our Knowledge Base.

We strive to help your plants thrive.