Welcome to ‘Smart Humidity’

Humidity. It’s one of the most critical elements in cannabis cultivation. But how many growers truly understand best practices when it comes to controlling humidity and what levels are ideal not only for minimizing disease, but also for maximizing plant health and yield? What are the benchmarks that can help guide you in your own facility, especially if you’re facing challenges with regulating humidity?

Cannabis Business Times (CBT) set out to find some answers. Our first-ever “Smart Humidity Special Report,” made possible by support from Quest Dehumidifiers, is packed with data from proprietary research, and insights from cultivators and experts on just these topics. The report will give you an idea where your humidity-control practices fall among your peers, tips for controlling humidity, why it’s so important to apply smart strategies and more.

Note: Totals may be slightly lower than or exceed 100% due to rounding.

Humidity control can be the bane of some cultivators’ existence. Rapid temperature drops into night cause humidity to jump upward, often into the danger zone. Daytime heat, or heat from lighting, causes humidity to drop; thirsty plants can wilt under that stress. But temperature is just one consideration toward controlling humidity; there are other factors that come into play, too. We will dive more deeply into many of these factors on the following pages.

When humidity levels aren’t just right, cannabis crops and your employees suffer. Many growers know that low humidity and dry conditions can create an appealing environment for spider mites, and high humidity can create an environment ripe for Botrytis, among other diseases.

What some may not know, however, is that in addition to the obvious risks to crops, you and your staff could also face health risks. “The combination of warm temperatures and high humidity found in many indoor marijuana grow operations can fuel extensive mold growth,” stated Dr. Martyny in a press release from National Jewish Health, regarding a study of the potential hazards of cannabis cultivation. “Airborne levels of mold spores that we found inside these structures may subject the occupants … to significant health hazards, especially allergies, asthma, hypersensitivity pneumonitis and other respiratory diseases.”

With these risks, it’s not surprising that more than three-fourths of cultivators who participated in CBT’s research said that humidity control is either very concerning (48%) or concerning (30%). And just 3% of participants said it is not a concern.

Growth Stages and Humidity Control

While most growers agree that humidity is a concern, they are not in agreement on the optimal humidity levels at various growth stages of the cannabis plant. And while many growers admit to being unsure of their humidity-control practices, others say that their optimal room humidity levels absolutely work for them.

For clone rooms, 19 percent of research participants said the ideal humidity level is 56%-60%. The same number of respondents said that, ideally, the humidity level should fall in the range of 76% to 80%. In all, the research showed that desired humidity levels in clone rooms varies from 40%-45% to above 80%.

For veg rooms, study participants’ responses varied almost as much, with the same number of respondents (10%) saying the ideal humidity level in these rooms is 40%-45% as those who said 71%-75%. The largest number of respondents (22%)—well shy of any kind of majority—indicated that their ideal humidity level in veg rooms is 56%-60%, followed by 18% who said ideal humidity in these rooms is 61%-65%.

In the flowering stage, growers came closer to a consensus. Nearly three-fourths (73%) of respondents said the optimal humidity level in flowering rooms is in the range of 40% to 55%. Eighteen percent said 56% to 65%. While 3% of cultivators said that their ideal flower-room humidity level is in the range of 76% to 80%, none said that above 80% humidity was ideal.

The late flowering stage saw even more consensus among cultivators in the study. Nearly two-thirds (64%) indicated that the optimal humidity level in the final stages of flowering is in the range of 40% to 50%. Within that range, more cultivators (39%) said that 40%-45% was optimal than those who said 46%-50% was ideal (25%).

Just 4% said that humidity levels during late flower are ideally above 70%, while just 1% said they prefer humidity above 80% in this stage.

Humidity and Mold Prevention

If there is any agreement about humidity in cannabis cultivation, it’s that its role is crucial. More than 80% of research participants said that humidity control helped them prevent or resolve a mold issue in their grow. Here’s what some cultivators reported:

“In addition to maintaining strict cleanliness protocols, we have found that by keeping the humidity down during flowering, we have no mold issues,” commented Rick Harder, owner/grower of Oregon Cannabis Authority, LLC.

“Molds are part of the natural environment, and can be found everywhere—indoors and outdoors,” commented another cultivator who wished to remain anonymous. “Mold is not usually a problem, unless it begins growing indoors. The best way to control mold growth is to control moisture.”

“It helps keep the mold and pest problem down. Drastically,” said Jeff Lobdell, assistant grower at Strainwise in Colorado.

“By creating a vapor pressure deficit [VPD, the difference between the amount of moisture in the air and what the air can hold at that temperature] in the flowering bays of our 2-acre greenhouse with our … automated environmental control system, Strawberry Fields has been able to prevent the growth of powdery mildew and Botrytis on over 25,000 lbs. of cultivated marijuana and has passed roughly 200 microbial tests, making it safe for consumption and available for wholesale,” explained Samuel Thoman, chief of business development for Strawberry Fields in Colorado.

19 Tips for Regulating Humidity

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

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 the VPD in the optimal range (or as close to it as possible), especially in the early stages of the plant’s 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. [Using] a humidifier during ‘lights on,’ and having enough dehumidification power when the lights are off in the 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]

How We Did It: 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. Participants are readers of Cannabis Business Times or subscribers to Cannabis Business Times’ weekly enewsletter. The link was also distributed via Cannabis Business Times’ social media channels.

Cannabis used to be so colorful: Acapulco Gold, brown Colombian, bright green Oaxaca big bud and, our personal favorite, redder-than-red Thai stick. The colors were the result of a variety of drying techniques that often involved drying the product under the sun, whose energy enacted chemical changes in the plant material, changing its color. This change is not something we see much of today because everyone cures in the dark to purposely avoid color change. Maybe it’s time to turn back the hands of time and see if we can learn anything.

Ask anyone what is happening in the drying room, and they will all answer “moisture removal.” Ask them what is happening in the cure room, and the answer, more often than not, is going to be “burping.” Despite a lack of specific knowledge about what is actually happening to the plant during the process, some growers say they are able to change and enhance the potency and effects during cure. If they can, there must be some chemical reactions going on. This would be really exciting because if we can identify and understand those reactions, we can leverage them. Let’s see if we can find any signs of those reactions.

A Cure-ious Comparison

The current wisdom on cannabis curing seems to be borrowed from tobacco curing practices. Cannabis producers use the same terminology used in tobacco processing. But under the hood of tobacco curing, terminology is where the similarities with cannabis curing end.

Being the most researched horticulture commodity in the world, there is plenty of tobacco curing research to dig through. The Wikipedia entry on tobacco curing has a good summary: “Curing and subsequent aging allow for the slow oxidation and degradation of carotenoids in the tobacco leaf.”

The oxidation of carotenoids produces color changes, which explains why tobacco curing is often called color curing. If we are looking for signs of chemical reactions, the color change is a clear sign of them. In contrast, cannabis that comes out of cure the same color it went in suggests that compared to tobacco, cannabis is not undergoing significant chemical changes in the typical dry and cure process. Compared to four to eight weeks of tobacco drying and curing, sometimes followed by a fermenting process, we can guess that the chemistry of cannabis material dried in one week does not change much before moisture levels drop below where biological processes and many chemical reactions can continue.

Tobacco curing does not just change the color of the leaves, it changes the flavor and aroma as well. As carotenoids degrade, they produce aromatic compounds that contribute to the tobacco’s distinctive aromas and flavors. Curing also changes the amount of sugars in the leaves, which also affects flavor. Add practices such as flue curing (heat treatment) and fermentation to the picture, and we can see that tobacco manufacturers employ a wide range of processes to produce leaf-chemistry changes. In comparison, the quick drying processes we use with cannabis have little chance of inducing chemical reactions.

In tobacco, the color-change period happens first and at humidity levels of 80 percent to 90 percent, and temperatures up to 105°F. The drying phase happens next at temperatures up to 140°F, and the final drying phase happens at temperatures above 140°F.

Tobacco leaf is commonly 25-percent sugar by weight, according to “Guidelines for Temperature, Humidity and Airflow Control in Tobacco Curing” by researchers at the University of Georgia. Flue-cured tobacco produces higher sugar content, while air and sun curing produce lower sugar content in the leaves.

If sugar levels can affect smoking smoothness in tobacco, maybe controlling it in cannabis could provide similar effects. To find out, we would need to look at using slower dry-down rates and heat applications, and, possibly even try to ferment the product to see exactly what changes we can induce in the plant’s chemistry. We would also need to examine whether any of those treatments produces a clearly superior cannabis product.

One thing is abundantly clear, whatever we are doing in our cure spaces, it’s not the same thing happening in tobacco curing barns.

Calling All Experimenters

The drying step for cannabis removes the majority of moisture from plants, and the humidity and temperature of the drying environment controls how fast moisture migrates out of the plant material. As opposed to cannabis, tobacco curing happens under the influence of heat, so here is something for someone to experiment with: heat curing. For that matter, someone should also try cold curing.

During the drying phase, water lost from the plant material carries with it aromatic compounds including ketones, alcohols, esters, terpenes and more. These terpenes are not the ones we typically talk about in the plant’s resin. They are contained in the plant material, like tobacco. It is reasonable to expect that as the “plant tissue” aromatics diminish, the aroma of the dried material becomes dominated by the terpenes contained in the resin on the trichomes.

This causes us to wonder if the dreaded “grassy” or “hay field” smell is the signature aroma of drying plant tissues, while the lasting aromas we get even after a year in storage are due to the terpenes contained in the resin that exists outside the plant material. Evaporation is not a chemical reaction (it’s a state, or phase change), so we don’t see much that suggests chemical reactions happening in during drying. We can, however, recommend a test for growers to vary the dry/cure conditions and monitor how long it takes for unwanted odors to dissipate, and which variable is responsible for the difference.

Test #1

Chlorophyll is a great place to look for chemical reactions. Popular literature ascribes unpleasant tastes to chlorophyll in leaves, and many people talk about getting rid of chlorophyll as a key goal of dry and cure. The green product rolling out of the typical cure room tells us chlorophyll is clearly not being destroyed, and people don’t seem to be turning it down, so does chlorophyll really play a role in aromas?

To find out, take some material and dark-cure it. Also cure some of the same material in sunlight, or under lights, until you get to the desired moisture level. Odds are that the light-cured material will not be the same color as the dark-cured material. The loss of the green color is the indication that the chemistry of the material has changed as the sunlight broke down the chlorophyll molecules, removing the “green.”

Now for the taste test. If the light-cured material gets higher marks from testers than the dark-cured material, we have fairly conclusively shown that chlorophyll is an important variable in the aroma equation—and that maybe we should be adding lights into our drying spaces immediately. If the tastes and aroma are largely the same for both green and not-green product, we will know chlorophyll is not the place to look for taste and aroma enhancements.

Test #2

Where does this leave us? In need of testing that enables cultivators to relate drying and curing techniques and schedules to aroma. First, dry some flower quickly, and compare that to flower dried over a six-day period. This will quickly establish how important the dry period is and provide feedback for fine-tuning.

We are very aware that the typical quick-dry times for cannabis are driven by a financial pressure that is never going to let up. That pressure is going to require anyone trying to lengthen their dry and cure time for better quality to have some pretty strong evidence that a longer dry/cure process is going to produce more revenue. A few simple tests seem reasonable to validate the current dry time and resulting quality, or indicate that minor changes in dry and cure have a potential worth that warrants further experimentation.

The Lab Test

What about the claims of better potency and altered effects? With labs now readily available to growers, claims can be validated or bounced easily. So when looking to dial-in a cure room, lab results will tell us if product chemistry is significantly different before and after cure. No more guessing.

Drying and curing processes are not insignificant to production costs, and that makes them a lever. Since you can move anything with a big enough lever, we need to find out if dry and cure offers us a little leverage on quality—or a lot.

The “Emerald Triangle,” an area in northern California comprising Humboldt, Mendocino and Trinity Counties, has a reputation as the mecca of cannabis cultivation for its highly fertile soil, ideal climate and the scores of cannabis farming experts who have made the region their home.

Siobahn and Adram Darwish, owners of Blessed Coast Farms, are such experts, with second-generation experience growing cannabis.

I first met Siobhan and Adram at the Marijuana Business Conference in Washington, D.C. Siobhan, who has 15 years of cultivation experience, spoke with pride in being the first licensed farm in Humboldt County. She was relaxed, but had an edge about her that let everyone know she meant business: a true “Humboldt chick,” as another cultivator later referred to her.

Adram spoke about how he stepped away from the day-to-day of the farm to focus on the couple’s other business: Darwish Building and Consulting. That company helps other cannabis farmers in the Emerald Triangle get their businesses up to regulatory standards and assists them in the municipal licensing process.

“We are forever grateful to our community and state that we have this opportunity for our small family farms to be able to grow legally,” they said after the show.

Here, Siobhan discusses details about their organic farm, the licensing process in Humboldt County and provides perspectives on the future of the Emerald Triangle.

Brian MacIver: What can you tell me about your farm?

Siobhan Darwish: Our farm is licensed for 10,000 square feet of mixed-lighting cultivation and associated processing. We have two additional farms that are in their last stages of permit approval. One, also mixed lighting, is under construction ... and will feature approximately 200 lights and will be a fully perpetual production model. The last farm is off-grid and is natural-lighting only.

Blessed Coast Farms is full-sun and organically grown. The majority of the farm hands here are female, and we are proud to produce high-quality, clean medicine. … We do not use synthetic fertilizers or pesticides. We track water usage closely and utilize efficiency measures. When possible, we practice permaculture principles, and use local resources as often as we can. We believe that sustainability extends to setting a high standard for conduct, and we are working to educate the community that the emerging legal cannabis industry is contributing to society, not taking from it.

BM: You were the first grower in Humboldt with a local permit (awarded in June 2016). How was the licensing process there?

SD: The licensing process here in Humboldt County is based on land usage. We had been watching the ordinance drafts and worked hard to be in the right place at the right time when the final draft finally passed. Because we are a ‘new’ farm, meaning that cannabis had not been cultivated here before, we didn’t have any legacy infrastructure that needed to be improved before permitting. It’s a challenging process for many farmers to suddenly bring their infrastructure, farms and operations plans into compliance.

BM: How has being licensed affected how you do business?

SD: Being licensed affects every single decision that we have to make as a business. We have to plan and document everything, and make sure that we are not stepping out of bounds for any of the regulations or agencies involved. … With regard to our cultivation operations, we document water usage and rates, fertilizer applications, pest controls, etc. We try to include as much data into our garden journals as possible so that we will have a record later for things that we may not have thought would be important.

BM: What led to your decision to team up with your sister on your business?

SD: I have been living and growing in Humboldt County for 15 years and have since gained a great amount of knowledge on the topic of cultivating cannabis. Once our farm … became permitted, we needed help. Who better to help than your family? I called my little sister, Sloan Reed, and invited her and her partner out here from Utah to work on our farm. Sloan had no prior knowledge of farming, the culture in Humboldt or the cannabis industry.

BM: Many growers try to keep their growing methods secret, but you and your sister launched an educational YouTube channel called Grow Sisters to teach people how you cultivate. Why was that important to you?

SD: Grow Sisters came to life once Sloan and I realized how unique our story was. The opportunity to document our journey together was too golden to pass up. As Sloan learns how to farm, we will share our experiences with our viewers with the hope of helping to educate them in the world of growing cannabis. We aim to share knowledge and spread love.

For far too long, the farmers who believe in cannabis as a medicinal herb have been looked down upon in our society. We are honored to share our story with the world in hopes of shedding a positive light on the subject. Grow Sisters is designed to share knowledge, highlight women in the industry of agriculture, and express that there are many different ways to grow your own medicinal cannabis. Many lives, many different paths, because you can grow your own way.

BM: What are your plans for “Grow Sisters” this year?

SD: We plan on filming our 2017 Grow Season with instructional videos that we will be posting on our YouTube channel [bit.ly/grow-sisters-videos].

This project is important to us because sharing knowledge and educating people to grow their own promotes keeping cannabis in the hands of the farmers and not large corporations. Farming must be shared from generation to generation, or we all will perish.

BM: Many growers in Humboldt, Mendocino and Trinity counties were opposed to MCRSA and Proposition 64. Do you know of any other growers who have applied for the local license?

SD: There were nearly 2,500 applications submitted in Humboldt County for commercial cultivation. As of recently, of those 2,500, maybe 150 were complete applications. More applications will be completed as farmers are able to complete infrastructure improvements and engineering requirements. It’s difficult for many of these applicants to move forward because all the ancillary services, like engineering and surveying, were suddenly overwhelmed with demand. Many fly-by-night service providers are trying to fill the voids, and some farmers are paying a lot for very little progress.

BM: How are you preparing for the launch of the recreational market?

SD: We are sitting on the edge of our seats to see how California implements the recreational market. We have yet to see state-licensing details, but are preemptively preparing the documents and plans that we are anticipating will be required.

There are some conflicting laws in California about water sources and storage that puts many farmers between a rock and a hard place. We know that the state is working on legislation to solve this, but for those of us out in the fields, we have to have a solid solution now in order to be in full compliance.

BM: What has been your biggest challenge as a cannabis cultivator?

SD: Our biggest challenge in the past has been that organic cannabis sells at the same price as non-organic. Growing organic is much harder than growing conventional. We believe with the farm-to-table movement gaining momentum that consumers will become more aware of their medication and seek out organic.

These cultivation practices are what set us apart from other growers. We are blessed to be able to plant directly into the earth from Humboldt County native-grown soil. We pride ourselves on being a sustainable farm. Everyone who works here lives on-site; we reuse all plastics, recycling what we cannot. We make compost teas over buying chemical fertilizers in plastic bottles, and cultivate organically.

BM: What do you think the future holds for the Emerald Triangle?

SD: It’s a wide spectrum. Some people are going to do great, others are already struggling. Most are somewhere in the middle. As a whole, Humboldt County, Mendocino County and Trinity County hold the most experienced cannabis cultivators in the United States. The Emerald Triangle will thrive with its perfect growing climates and knowledgeable cultivators.

Responses were edited for length and clarity. Additional reporting by Cassie Neiden.

A number of techniques exist for increasing cannabis yields, including watering, lighting, fertilization and timing of vegetative and flowering periods. Here, we’ll highlight 5 of the most common pruning and training techniques used to maximize cannabis yields without significant capital investments. Most pruning and training should be undertaken while the plant is the vegetative stage, whether you’re employing these techniques indoors or outdoors. These techniques may be used independently or in various combinations to achieve maximum yields, depending upon the layout of your cultivation facility.

1. Removal of lower branches.

Most every style of cultivation operation will rely on pruning that includes removal of lower non-productive branches. This is best done early on in the vegetative stage and will encourage the plant to focus on the taller and more productive branches, increasing weight and size of colas the plant produces.

2. Removal of dead or moribund leaves.

This is especially important in an indoor cultivation operation, as lower leaves tend to begin to die as higher leaves grow and block light from reaching them. Removal of dead and dying leaves will minimize risk of disease and pests that can reduce yields, and allows the plant to focus energy on productive leaves and bud formation.

3. Regular pruning.

The continued removal of branches with long internodes or space between nodes on the lower part of the plant throughout the vegetative cycle is another common practice for indoor and outdoor cultivators.

4. Topping plants.

Topping is a pruning technique in which the main shoot is snipped down to encourage secondary shoots to grow with greater vigor. A plant may be topped multiple times, and each time it is topped, the number of dominant shoots will double.

5. Low-stress training.

This is a training method where instead of topping the main shoot, it is tied down and trained to grow in a horizontal fashion, which causes the other shoots to grow more rapidly.

With careful monitoring and experimentation, you can determine which pruning and training techniques work best for your operation and cultivar selection. And check out the August issue of Cannabis Business Times for 5 more tips on maximizing yield with little investment, including fimming, SCROG and super cropping.

Crystal Oliver is co-owner/founder of Washington’s Finest Cannabis, an outdoor cannabis farm licensed by the Washington State Liquor and Cannabis Board since August 2014. She also serves as executive assistant for Washington NORML and sits on the Cannabis Farmers Council Executive Board.