19 Tips for Regulating Humidity in Cannabis Grows

Special Advertising Section - Special Report: Humidity and Climate Control

November 22, 2021

Note: This article originally was published in the July 2017 issue of Cannabis Business Times as part of its “Special Report: Smart Humidity” supplement sponsored by Quest Dehumidifiers.

As part of this research project, Cannabis Business Times asked cultivators to share their strategies for maintaining optimal humidity levels. Here’s what they said:

1. “The use of a dehumidifier has been critical for my operations. Removing lower leaves as soon they begin to fade and adequate spacing between plants coupled with excellent air circulation. … Also, keeping the humidity level below 50% outside of the rooms.” — Scott Stanley, Owner/Operator, Artisan Greenery, Minnesota

2. “… A humid drying room could cause the plant to not properly dry. … I find that AC units work well. [So do] fans and dehumidifiers, but [they] require monitoring.” — Jaymie Vacura, Owner, CannaVision, Washington

3. “Cuttings need to retain moisture until roots show. Then, VPD [vapor pressure deficit] plays a role in veg and flower. And in flower, we do not want to invite molds or mildew of any kind with thick buds forming. … [Use the] correct equipment [fans, dehumidifiers, temperature control].” — Max White, Production Manager, Aroma Cannabis, Oregon

4. “We are located in a dry, high-altitude environment where day-to-night temperatures can swing 50 degrees difference. There was a learning curve understanding how to set up our automated greenhouse controls to properly deal with humidity spikes during our monsoon season. Keep an eye on incoming weather and make proactive adjustments to [automated] environmental control settings.” — Scott Holland, Director of Operations, Durango Organics, Colorado

5. “Dehumidification, circulation fans at top and sides of the greenhouse or room. Proper intake and outtake of fresh air. [Use] an automated environmental control system.” — Michael Redmond, Owner/Cultivator, Red Bud Harvest, Michigan

Note: Exceeds 100% because participants could select more than one option. The study was conducted during May and June 2017. Results are based on 104 research participants who indicated that they own or work for a cannabis cultivation business. The survey was conducted online with a link provided for participants.

6. “Final results of an indoor grow are greatly influenced by the way growers keep in control of parameters that influence their plants’ growth. There are two basic factors that can easily be forgotten when we’re busy thinking of other ways to increase yields, size and overall health of our plants: temperature and relative humidity. [Use] humidity and temperature data loggers and recorders.” — (preferred to remain anonymous, state not provided]

7. “Keeping VPD in the optimal range, especially in the early stages of plant lifecycle, ensures optimal growth rates. Stomata on the leaves are more open, allowing the plant to uptake more CO2, and growth rates increase. PM and other issues are less likely to occur in the optimal RH/temperature range. [Use] a humidifier during ‘lights on,’ and have enough dehumidification power when lights are off in flowering rooms. Hygrometer, constant monitoring, and dehumidifiers/fans are automated.” — (preferred to remain anonymous, Washington)

8. “Your grow/flowering room should have at least two temperature and humidity gauges.” — [preferred to remain anonymous, California]

9. “We change watering strategies slightly when we have days where we will fight high humidity.” — Trey Anderson, Director of Production, IESO, Illinois

10. “Keeping optimum soil moisture. Containment of run-off, air flow to reduce micro-climates.” — Eric Edgerton, Owner, Tilth LLC, California

11. “I use a HOBO data logger that monitors and records both temperature and relative humidity every 5 minutes. The data is accessible via Bluetooth on my iPhone. … Lots of air movement, large dehumidifiers and drip watering systems.” — Rick Harder, Owner/Grower, Oregon Cannabis Authority LLC, Oregon

12. “Keep your equipment clean and serviced.” — Mark Robertson, Owner, Going Green, Washington

13. “Use commercial HVAC/humidity control systems designed for plants, not people.” — [preferred to remain anonymous, Illinois]

14. “Dehumidify and ventilate the greenhouse while irrigating the crop to prevent trapping any unwanted humidity.” — Samuel Thoman, Chief of Business Development, Strawberry Fields, Colorado

15. “Have a dehumidifier or two for the night hours. Run the AC at a bit lower temperatures at night to extract moisture.” — Jason Roberts, Owner, Loving Kindness Farms, California

16. “Great air circulation.” — [preferred to remain anonymous, California]

17. “The more water (plants) I have in the room, the more humidity reduction I need.” — (preferred to remain anonymous, state not provided)

18. “As an organic dirt grower, I found that the more I paid attention to watering throughout flower and went light (i.e., let them get a bit thirsty from time to time), the less of a humidity problem. I use AC and a 90-pint dehumidifier for a 32-plant flower room of approximately 15 feet by 40 feet. And I run four 16-inch ... fans on low 24/7, oscillating.” — Keith James, Detroit High-Ons, Michigan

19. “Different strains may need different humidity levels.” — [preferred to remain anonymous, Washington]