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How To Manage Humidity & Prevent Mold In Your Cannabonsai Grow

Maximizing Cannabonsai success with Optimal Humidity

Maintaining the proper humidity levels in a small cannabis grow tent can be crucial for the success and quality of your cannabonsai projects. Luckily cannabonsai follow the same general requirements for other cannabis plants. The primary reason to care about optimizing humidity in cannabonsai grows is to prevent mold growth and maximize the results of the time and effort put into growing and maintaining or flowering a cannabonsai.

The Importance of Monitoring & Adjusting Humidity

During the seedling and clone stages, it’s best to maintain a humidity level of 65-70%. This allows the plants to take in water through their leaves while their root systems are developing.

As the plants enter the vegetation period, the humidity levels can be lowered by 5% each week, with an acceptable range of 40-70%. This is because the roots are now more developed and able to take up most of the water needed, with evaporation through the leaves providing cooling for the plants.

During the flowering period, it’s important to lower the humidity levels to 40-50%. It’s crucial to never allow the humidity to rise above 60%, as this can lead to mold and mildew growth. 


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Max (65% min)​


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Max (40% min)​


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Max (40% min)​

Maintaining the Proper Temperature

Without diving in deep on how temperature and humidity are connected, it’s worth noting that temperature and humidity are two factors that are closely related. When the air gets warmer, it can hold more moisture or humidity, so the relative humidity will be higher. When the air gets cooler, it can hold less moisture, so the relative humidity will be lower.

The optimal temperature for different stages of cannabis growth can vary depending on the specific strain and the conditions of the grow environment. In general, cannabis plants prefer temperatures that are cool during the seedling and clone stages, and slightly warmer during the vegetative and flowering stages. 

Here are some guidelines for the different stages of cannabis growth:


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Max (68°F min)


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Max (71°F min)​


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Max (68°F min)

Late Flowering

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Max (64°F min)

It’s important to monitor the temperature in your grow environment and make adjustments as needed to ensure that your cannabis plants are getting the optimal conditions for growth.

Seedling & clone stage: The temperature with the lights on should be 68-77 F°, with the lights off it should be 8-9 F° lower.

Vegetative period: The temperature can be slightly increased if desired, with the lights on it should be 71-82 F° and 8-9 F° lower with the lights off.

Flowering period: The temperature with the lights on should be 68-79 F°, avoiding high temperatures.

Late flowering period: The temperature can be slightly lowered to 64-75 F°.

Achieving Optimal Humidity & Temperature with the Right Equipment

To achieve the optimal humidity and temperature levels in your cannabonsai grow, it’s important to have the right equipment. A hygrometer and thermometer can help you accurately monitor the conditions in your tent. Humidifiers and dehumidifiers can be used to adjust the humidity levels as needed. Here are some products to consider:

Humidity and temp for cannabis

Raising Humidity

Generally speaking, you shouldn’t have to raise your humidity. If you’re working with fresh cannabonsai seedlings or clones, it’s easiest to simply make a tent out of a zip lock bag or clear storage bin than it is to blast your tent with moisture. If it’s a dry winter environment or some other reason more moisture is needed, start by adjusting your watering cycle to be when the lights first come on to encourage evaporation into the environment.

If that doesn’t work, there are a few products to consider:

  • Ultrasonic Cool Mist Humidifier: This compact humidifier is perfect for small grow tents and can be easily adjusted to maintain the desired humidity levels.
  • Evaporative Humidifier: This type of humidifier uses a wick, filter, or foam to absorb water from a tank and then blow it into the air as a cool mist.

Lowering Humidity

Humidity over 60% is almost certain to cause headaches during flowering or a cannabonsai. There are a few options for reducing the humidity in your grow tent however. There are a few other options I didn’t list like DampRid, rock salt, baking soda, other solutions I just don’t think work that well or are less environmentally friendly that those below.

  • Dehumidifier: This device removes excess moisture from the air, helping to lower humidity levels in your grow room. There are small ones that may fit right in your tent, but all must be drained and not many of the cheap ones seem to be well made.
  • Desiccant Dehumidifier: This type of dehumidifier uses a special material to absorb moisture from the air, making it a great option for small grow tents. This is what I’ve been using lately, though I opted for the clear kind. It’s “rechargeable” via drying out in the sun or oven and I like that it’s analog and inexpensive.

Additional Considerations

Clean air circulation is the cornerstone to optimizing any cannabonsai grow space. If you have a contained area, a circulating air system with a HEPA filter intake and a carbon filter exhaust are key.

You don’t need to break the bank however, as many DIY options are available for anyone willing to make it work. 

Just check out this HEPA air intake from Shan1784 on Grasscity

DIY HEPA Air intake for cannabis grow

Final Thoughts

By using the right equipment and properly managing humidity levels, you can successfully prevent mold growth and consistently produce healthy cannabis on your cannabonsai art. Investing in the right tools and monitoring your humidity levels will pay off in the long run and set you up for success if you want to get some bigger plants growing. That being said, if your grow is in the right ranges because you live somewhere temperate and dry or already have a climate controlled space, you may be off the hook.

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