Dehumidification – It’s All About the Dew Point

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Humidity is a critical factor in cannabis cultivation, one that is much discussed but also often misunderstood. It's about time we set the facts straight. DryGair explains...

The DryGair Writing Team
Hadar Fuchs-Rubal | Yanor Yazma | Rom Meir

The following is an article produced by a contributing author. Growers Network does not endorse nor evaluate the claims of our contributors, nor do they influence our editorial process. We thank our contributors for their time and effort so we can continue our exclusive Growers Spotlight service.

We want to help you keep your buds dry and healthy, so this article may be a bit long-winded. Take a deep breath, but don’t sweat. Or condense.


WHAT IS HUMIDITY?

Air is comprised of many different gases, one of which is water vapor - the gaseous form of water. The amount of water vapor in the air can measured via relative humidity (RH). This is basically the amount of water vapor in the air, as a percentage of the amount of water the air can contain.

RH is determined by two factors: the amount of water vapor in the air and the air temperature. With this in mind, we can understand the importance of relative humidity in a growing facility.


WHY DO WE NEED TO MAINTAIN A CERTAIN RELATIVE HUMIDITY LEVEL?

Humidity is a major factor in the cannabis industry due to the dreaded Botrytis, a moisture loving fungus, most commonly known as "bud rot", elsewhere referred to as gray mold.

Humidity control means bud rot prevention. That's the bottom line.

Due to the dense nature of the cannabis bud, it's highly susceptible to a build-up in humidity. This is because plants are their own internal humidifiers, continuously emitting water vapor through their leaves. In cannabis buds, this internal humidification is amplified because the buds themselves contain leaves, commonly referred to as "sugar leaves". Because the bud is dense, this humidity gets trapped in the air contained within and around the bud.

While humidity is water vapor in the air, the real enemy is liquid water on the plant, because Botrytis needs liquid water to prosper. As temperatures vary between day and night, and different places around a grow change in temperature, water will condense on cold surfaces. And this is the tricky part, as the plant itself may be the cold surface! Plants transpire as they cool themselves off, sort of like sweating, rendering them colder than their immediate environment. The humidity inside a dense bud will condense on cold surfaces, creating liquid water that is great for mold and a major concern for growers.

To better understand the relationship between humidity and air temperature, we should take a look at the dew point.


DEW POINT – THE KEY TO CONDENSATION PREVENTION

The dew point is the point at which air becomes saturated with water vapor, forcing the water to condense out of the air, from a gas into a liquid. Basically, it's the point at which temperature has dropped enough to force water to appear out of thin air (literally).

Click to see full size.

This may not seem intuitive because water vapor is invisible, so we'll use an everyday life example:

When you pour a cold drink into a glass, you'll notice water forming on the outside. This happens because the cold drink lowers the temperature of the glass, pushing it beyond the dew point. The water vapor from the ambient air condenses onto the outside surface of the glass and that’s where you get the formation of water droplets.

This is the basic concept. The dew point is the temperature at which water vapor in the air (humidity) turns into liquid water.


HOW IT WORKS

Temperature and relative humidity are intertwined. It's easy to think of air as a sponge in this scenario; it contains water up to a certain point and once it is full, water begins to appear (or condense). If the temperature is constant, we can reduce the relative humidity by removing water vapor from the air. This would stop the appearance of water.

But when temperature changes, the size of the sponge changes. If we continue the analogy, hotter air means a bigger sponge, and colder air means a smaller sponge. As a result, the amount of water in the sponge remains the same, but the relative amount changes. Likewise, hotter air can contain more water than colder air can. When temperatures rise, relative humidity drops, reducing condensation. As such, water condensation can be managed and prevented through control of both humidity and temperature, such as with DryGair's dehumidification systems.

This is the important part - the dew point is basically a breakdown of this relationship. The following graph represents the dew point as a function of RH at a given air temperature:

Graph of Dewpoint vs. Air Temperature at 70% Relative Humidity. Based on the Magnus-Tetens approximation.

This graph represents 70% RH. You may notice that at an air temperature of 70°F (X axis), the graph aligns with 60°F dew point temperature (Y axis). This means that if your greenhouse air is currently at 70% relative humidity at 70°F, you can go as low as 60°F before liquid water will appear in the greenhouse. If any surface in the growing facility reaches 60°F or below, water will condense onto it. Cooler surfaces are typically ceilings and walls, which have greater contact with the outdoors, metal pipes and railings, which can sit at different temperatures, or as we mentioned earlier, the plants themselves.


A SMARTER APPROACH

A combined approach, based on knowledge, allows us to do the minimum. We don't mean minimum care, we mean minimum cost.

Understanding what the dew point is and the factors that affect it provides us a better understanding of what's really going on in our operation. What really happens when we heat up, or allow the air to cool down. It's not just about temperature, it's about humidity as well and the dew point encapsulates this.


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About the Authors

DryGair’s writers include a team of experienced engineers, agronomists, and economists. They specialize in climate control in closed growing facilities and practical solutions for effective climate management.


Motorleaf’s Vision for AI in Grow Operations

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In this Growers Spotlight, we spoke with the CEO of Motorleaf, Alastair Monk, about what his company is doing and their vision for Artificial Intelligence in the Cannabis space.

Alastair Monk

The following is an interview with industry experts. Growers Network does not endorse nor evaluate the claims of our interviewees, nor do they influence our editorial process. We thank our interviewees for their time and effort so we can continue our exclusive Growers Spotlight service.


Abbreviated Article


Editor's Note: Growers Network appreciates its readers! If you are limited on time, we are now offering abbreviated versions of our articles. Click below to view.

If you like the abbreviated article, let us know in the survey at the bottom of the article! We're always interested in hearing your feedback.

If you want to read more, you can read the full article below.


Implementing Artificial Intelligence

Montreal is the center of AI in the world right now.
Alastair Monk

The Market for AI

Cannabis production will become a race to the bottom in terms of what producers can charge for their product.Alastair Monk

About Alastair and Motorleaf

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Want to get in touch with Motorleaf?

You can reach them via the following methods:

  1. Website: https://motorleaf.com/
  2. Phone: (888) 687-5301
  3. Email: info@motorleaf.com

Resources:

Want to check out some different controller and artificial intelligence companies in the cannabis space? Take a look at these:

  1. Motorleaf
  2. Kindbot
  3. Grow Diaries
  4. Argus Controls
  5. Wadsworth Controls
  6. Priva
  7. Link4 Controllers

Do you have any questions or comments?

Feel free to post below!


About the Author

Chris DeWildt is a graduate of Grand Valley State University and Western Kentucky University. In addtion to writing for Growers Network he is also a novelist


Evolutionary Origin of Cannabis: It’s a Little Fuzzy, Man

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In this article, Growers Network explores the origins of the Cannabis genus, looking at both the problems with genetic studies and the plant's historical use by early Homo sapiens.


Difficulties in Determining Origin


The biological genus Cannabis has a long, documented history of use by humans. Through archeological and historical evidence, researchers in various disciplines have been able to hypothesize a timeline of not only when Cannabis was first utilized by humans, but how it migrated with us as well. The natural history and biogeography of the genus before human utilization is hard to determine precisely, but genetic and archaeological evidence do give us a few clues as to its likely evolutionary range. Presented here is a partial summary of current scientific thought that will explain the hypothesized natural history of Cannabis, in addition to the evolution of the plant alongside humans.

Limited genetic research has been done to determine specifically where the oldest known populations of Cannabis exist and what their relationship to a common ancestor might be. Genetic research has focused primarily on whether any true speciation has occurred within the genus or whether the different “types” are just subspecies. This is difficult because the definition of a "species" can be a little squishy depending on whether you are talking to a biologist, cultivator, or a layperson. The simplest definition of a species is a population of organisms who can breed with one another and produce viable, fertile offspring. The entire Cannabis genus fits this definition, with all variations capable of breeding. This may seem to settle the issue, but another school of thought would argue that although the plants can breed, they don’t because of geographic barriers, and as a result should be considered different species despite their breeding potential. The literature is split on this topic, with some researchers proposing a single Cannabis species made up of three subspecies (sativa, indica, ruderalis) and others treating the subspecies as species in their own right. So despite the powerful tools at our disposal, there are already several questions that make determining Cannabis’ origins problematic before we’ve even started.

Then we need to tackle other issues preventing a clear picture of the Cannabis family tree. One of the first problems is the lack of fossil evidence prior to human use of the plant. Cannabis doesn’t tend to fossilize, given the locations it grows in naturally. Secondly, the characteristics that make Cannabis a relatively easy plant to grow also make it difficult to determine its point of origin; Cannabis can rapidly adapt to new regions and is an annual plant, so a high genetic diversity in a specific region is not necessarily indicative of antiquity. Even if we are able to identify “wild” Cannabis, it is most likely a “feral” variant with no real information about the ancestral type.


The result of these complications is that the best evidence to hypothesize the endemic origin of Cannabis is an examination of the ecological requirements of the plant and its reproductive strategies.

As mentioned previously, Cannabis is a relatively easy plant to grow (the nickname “weed” isn’t an accident). Cannabis will readily spread and grow without human intervention in the wild, quickly adapting to a variety of variable conditions within its range of ecological requirements. For example, the sun and heat loving Cannabis plant is more shade tolerant than other crop species, allowing for a wider range of suitable habitats. Even if we narrowed down likely origin spots based on these propagation requirements, we find that these hospitable ranges shifted several times during glacial and interglacial periods. So what do we know?

Not much.

The best hypothesis suggests that Cannabis originated in Central Asia, mostly likely within what are now the borders of China. Though this is a general consensus among many researchers, others hypothesize the location to be farther south into what is now India, Afghanistan, or even northern Eurasia.


Cannabis and Ancient Peoples


Though it’s hard to nail down exactly where Cannabis first took root, we have a better handle on the coevolution of the plant in relation to Homo sapiens. Given the ecology of the plant, its spread was inevitable. The working hypothesis is that around 10,000 years ago, most likely in central Asia, modern humans discovered the plant and found that the seeds were a valuable resource for food and oil as well as fiber for rope and eventually clothing. The oldest evidence of this use is in China where hemp fabric was discovered as well as hemp shoes that date back about five-thousand years.

A proposed map of how Cannabis traveled with humans as they spread around the globe.

We know that Cannabis thrived in close proximity to humans, even prior to the advent of agriculture. As our ancestors utilized the plant, discarded seeds readily germinated and grew around their camps and latrines, and as a result the plants followed early humans as they traversed the old world continents. It’s not surprising we curious primates would utilize the versatile weed for everyday needs of survival, but when did we notice the intoxicating effects of the plant?

Most likely the psychotropic effects of Cannabis use were discovered when the plant was burned as campfire fuel, the smoke wafting through the air and inhaled as our ancestors cooked or rested or just tried to warm themselves. Our ancestors found themselves relaxed and calmed. It allowed them to forget their aches and pains for a time. This phenomenon would have been considered a welcomed distraction from the extreme hardships early humans faced, and it’s not surprising that Cannabis, and other psychoactive substances, were often considered a gift from the gods and incorporated into religious ritual and spiritual pursuits, and eventually even recognized for their medicinal properties.

It would be nice to be able to say with certainty where the Cannabis genus first appeared, but a logical hypothesis is all we have, given the nearly ubiquitous modern distribution of the plant. Hopefully, interested parties will soon fund a more comprehensive effort to determine the plant’s origin. A few efforts that have already shed a great deal of light on many of the anthropological questions surrounding Cannabis, and more research would go a long way.



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About the author

Chris DeWildt is a graduate of Grand Valley State University and Western Kentucky University. He worked in education and publishing for ten years before joining the team at Growers Network. In addition to editing the GN blog, Chris also works on the Canna Cribs series.


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Integrated Pest Management

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In this Growers Spotlight we interview Jordan Mello, the Master Grower for In Good Health, a state-licensed, non-profit medical marijuana dispensary located in Brockton, MA.

Jordan gives us an insider view on Integrated Pest Management (IPM), and explains why MA IPM policies will most likely have an impact on current and future state regulations with regard to cannabis testing, quality control, and pesticides.

If you have any questions related to IPM, growing in MA, commercial cultivation, or direct questions for Jordan, you can post in the comments section below.

What is the definition of IPM?

Integrated Pest Management (IPM) is the careful consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keep pesticides and other interventions to levels that are economically justified and reduce or minimize risks to human health and the environment. IPM emphasizes the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms.


Massachusetts's IPM

We apply pesticides about 3 days a week, with a rotation of Biosafe Systems ZeroTol, a neem oil product, and Procidic.Jordan Mello

Jordan Mello's IPM Regimen

Regulations change constantly. You need to cover your bases and be cautious on things you bring in.Jordan Mello

Growers Network Questions

The interesting thing about my job is that none of my days are ever the same.Jordan Mello

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Resources:

  • How to manage Spider Mites -- University of California IPM
  • Pesticide use in Cannabis Production -- Beyond Pesticides
  • Pesticide Database -- Pesticide Action Network
  • National Organic Program -- USDA
  • IPM 6-Step Approach -- MA Energy and Environmental Affairs
  • IPM Kit for Building Managers -- MA Department of Food and Agriculture Pesticide Bureau

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    About the Author

    Hunter Wilson is a community builder with Growers Network. He graduated from the University of Arizona in 2011 with a Masters in Teaching and in 2007 with a Bachelors in Biology.