News and Best Practices

Understanding Humidity Could Prevent 10% Inventory Loss

October 17, 2016

Humidity is one of the blessings and curses of any grow environment. If it’s too humid, your plants get soggy. If it’s too dry, your plants will wither. If you get the humidity “just right,” you’re in the Goldilocks zone, and your story will have a happy ending.

Keeping cured buds moist is one thing. But getting the buds to a perfectly cured point is quite another, and humidity can be your best friend in this situation—or your worst enemy.

What is humidity?

Humidity is how much water vapor is in the air. Because plants depend on water to survive, water in the air is just as important as the water you’re feeding them. With high humidity, there’s a lot of water vapor in the air, and hot air holds more water than cold air.

Air can hold only so much water, too. Once the air reaches its saturation point, precipitation appears in the form of fog, rain, dew and so on. If you’ve got dew droplets forming in your grow room, then you’ve gone well past the saturation point.

Scientists measure humidity in three ways:

  1. Absolute humidity measures how much water (in grams) is in the air at a given temperature. For example, our grow room has a humidity of 60% and a temperature of 70°F. That means we have 60% of the absolute humidity that we could have in this room at 70°F.
  2. Specific humidity measures how much water we have in relation to the amount of air.
  3. Relative humidity measures the absolute humidity in relation to the maximum possible humidity at a given temperature. We always express relative humidity as a percentage, which makes it easier to conceptualize (unlike the other two measurements, which rely on the metric system and additional dimensions).

All three measurements of humidity are useful, but we’re most interested in the functionality of the measurement. For example, absolute humidity gives us an exact measurement, but it changes with the temperature. It’s too complicated to predict humidity effects with absolute measurement. You’d have to take into account the area you’re measuring and the temperature, then extend those calculations to your grow or cure room.

Relative humidity, on the other hand, gives us a single number. That number, given our typical grow or harvest conditions, can tell us a lot. Meteorologists use relative humidity to predict storms, because that percentage tells us the skies hit their saturation point at 100%. In a grow room, saturation means dew and foggy windows. All that extra precipitation can wreak havoc on your watering schedules, because too much water can be a bad thing for plants.

The higher the relative humidity, the higher the temperature will feel, too (regardless of the actual temperature). Plants will respond to too much humidity just as they would if your room was too hot.

In grow rooms, some of our more volatile or unstable materials may interact with water vapor. Fertilizers, pesticides and other chemicals will report humidity effects on their labels, and these humidity levels are always reported as relative humidity.

How does humidity affect a harvest?

If you’ve gotten to the point where you can finally harvest your buds, then you have some inkling of how humidity works during the grow. Humidity for harvests is a little different, because you need to maintain a specific amount of humidity at all times for a proper cure.

Drying and curing are related, but they’re not the same thing. Drying means getting rid of the water in the buds. Curing is a process of breaking down the bud’s sugars, starches and chlorophyll. Curing is how we get those distinctive aromas from our favorite strains. It’s also how we get rid of the lawn-clipping flavor that taints low-quality bud.

The trick to a correct cure is to let a certain amount of moisture leave the buds in a slow, controlled manner. We need to keep some moisture in the air at all times and, in the end, we need to lock some moisture in our buds, too. If the buds get too dry too quickly, we can lose terpenes and cannabinoids in the process as well.

During the cure, you’ll want your humidity around 45-55% at 70°F. Some growers may go a little higher, from 55-65%. Because humidity and temperature aren’t consistent in large areas, you may want to do your curing in containers.

Each container should have its own hygrometer. You should also have hygrometers stationed throughout the cure room, too. Remember to take measurements from high and low positions in the room, to get the full picture.

The ideal humidity range depends on the strain. Some strains are known to retain a lot more moisture than others. Bigger, more compact buds take longer to cure, and may require lower humidity than smaller, less dense buds.

How humidity affects a retailer

In an era of seed-to-sale tracking, the weights of your buds have a huge impact on your business. For one, some customers aren’t entirely trusting. They may weigh their 1/8 oz. sack once they get home, just to ensure they’re getting their money’s worth. If they weigh your product and come up short, they may think they’ve been robbed.

In reality, buds are always losing moisture. They move from the curing room to their packaging. The shelves of most dispensaries and retail stores don’t monitor humidity the same way a harvest room will. The buds will continue to evaporate, and the weight you had prior to packaging may have been higher than the weight of the package going out the door.

You may also lose out on sales if your buds lose too much moisture. If you’re selling totally dry buds, then you’re actually selling more plant material than you should. According to Charles Rutherford, the Director of Business Development at the humidity-control company Boveda, this loss of weight can be incredibly costly. Cannabis retailers, he says, are “losing money as it sits on the shelf. It’s not uncommon for someone to lose 10 percent of their inventory to evaporation.” And that 10 percent is his conservative estimate.

Then there’s the issue of business records. Washington and Colorado require meticulous records regarding product weight. If there’s a major gap between the harvest weights and the sold weights, then regulators may come knocking on your door.

The good news is that there are ways to preserve moisture in your buds. Humidors, humidifier packs, and even fruit peels can keep your humidity levels in the right zone. Proper humidity means proper weights, and proper weights keep everyone happy.


By Randy Robinson
Dispensary Management Today articles are for informational purposes only and should not be considered legal guidance or advice on dispensary operations. You should contact an attorney or a qualified cannabis consultant for specific compliance and dispensary/retailing advice.
© 2016 CAN Performance Group, LLC. All rights reserved.



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