Galenas, in Akron, Ohio, keeps its RH levels around 65% during vegetation before gradually lowering between weeks three and eight of flowering.
Photo by Patrick Williams

Managing the humidity levels in a cultivation operation is absolutely critical to maintaining a growth schedule and getting optimal production out of plants. If humidity levels creep too low during the vegetative growth phase, plants will be stunted, and you will lose weeks of production waiting for them to pull through. If humidity is too high, you are at risk for disease outbreaks, including the infamous bud rot.

Here are six tips to help you better manage cultivation facility humidity.

1. Track indoor and outdoor environmental data.

Humidity changes inside a grow are not dependent upon just the actual relative humidity (RH) of the incoming air, but also the grow room temperature. Many cultivators have struggled because they have taken plans from a cultivation operation in California or another western state and dropped them into the Midwest or Northeast without accounting for the differences in ambient outdoor conditions. Tracking outside environmental data throughout the year is the best way to anticipate patterns and make changes in advance.

2. Steam your way through veg.

Plants like a lot of humidity in the vegetative growth phase. Of course, each cultivar likes a slightly different environment, but generally speaking, at our Galenas facility in Akron, Ohio, we keep relative humidity around 65% to maximize transpiration and keep plants healthy and growing at their maximum rate. This humidity level keeps the plant’s stomata open, which keeps water and nutrients pulling up through the plants. Nutrient mobility is the key to healthy plants.

3. Stage your dehumidifiers based on other environmental changes.

Humidity levels tend to spike right after the lights go off. One way to offset this spike is to ramp up dehumidifiers from a half hour before to a half hour after lights turn off. Pay attention to those environmental logs.

4. Transition gradually.

Plants can tolerate lower humidity as they move through the flowering period. We like to keep our RH at 65% for the first week of flower. This minimizes plant stress during a naturally stressful part of their life cycle. Between weeks three and eight, we gradually lower the RH.

5. Avoid swings to prevent disease.

Sporulation of powdery mildew can occur if there are large swings in humidity. Avoid creating humidity from flood-style watering, and make sure to remove any standing water if overflows or leaks in irrigation systems occur.

6. Work with your product manufacturers.

We use LED lights throughout our facility, and the supplier provided a cultivation guide. It provides mounting heights and dimming percentages at specific distances, as well as temperature, photosynthetic photon flux density (PPFD), CO2 and RH management guidelines. Also included is a great Vapor Pressure Deficit chart.

Geoff Korff is founder and CEO of Galenas, a Level II cultivator in Ohio’s medical cannabis program, operating out of Akron. Christine DeJesus is director of cultivation at Galenas.