Is 70% Humidity Too High for Cannabis?

70% humidity is generally too high for cannabis, especially during the flowering stage. Here's a breakdown of why and what the ideal humidity levels should be:

 

Ideal Humidity by Cannabis Growth Stage

Stage:	Ideal RH (%):
Seedling/Clone	65–70%
Vegetative	50–70% (60% sweet spot)
Flowering	40–50%
Late Flowering	30–40%
Drying & Curing	50–60% (drying), 58–62% (curing)

 

Why 70% RH is Too High for Cannabis

Increased risk of bud rot (botrytis) — a mold that starts inside dense buds and ruins the crop.

Encourages powdery mildew.

Weakens overall plant structure due to excess moisture.

 

Management When Humidity is too High in Grow Room

Lower the humidity:

Use a professional industrial-size grow tent dehumidifier. Dehumidifier is the key and the most effective way to control the humidity. The selection, installation, and control of the wall mounted dehumidifier with drain hose are interlocked without any errors. A slight negligence may lead to a reduction in marijuana production. If growers want to achieve efficient planting and maximize profits, they need the help of professional dehumidifier manufacturers.

 

Increase airflow with oscillating fans:

Improve exhaust ventilation to remove humid air.

 

Monitor RH and temperature together:

Aim for a VPD (vapor pressure deficit) balance — too much RH with warm temps creates mold-prone conditions.

 

Use a hygrometer:

Place one at canopy level to get accurate readings.

 

Let me know what stage your plants are in, and I can help you dial in the perfect environment. The use of grow room dehumidifiers requires professional instruction. Preair has accumulated many precious production, installation, and control experiences of cannabis dehumidifiers. Need help to precisely control humidity in your grow rooms? Please get in touch with us as soon as possible.