How To Dry Cannabis Like a Pro

Do you know how to dry cannabis?

Drying cannabis is, without question, the most crucial step in all growing operations, and it is often the most neglected. People spend eight weeks or more growing their plants, only to treat them horribly during the drying process. Drying is not a particularly special process; however, it does require time and attention to maintain specific parameters for your dry room’s environmental conditions and airflow.

Dry Cannabis: Optimal Conditions

I often hear the industry talk about ‘60°F at 60%’ as the optimal conditions for drying. I know these conditions work well; however, I can’t say that these are the best conditions for drying cannabis. These conditions are the lowest temperature and humidity that off-the-shelf “commercial/residential” air conditioning can deliver to a space. Old-school growers always speak of “low and slow” when it comes to drying, and this approach also aligns with the lowest temperature they can easily maintain throughout the year. 

Sixty per cent humidity is already reaching a point where the surface tension of a cold surface in the room will overcome the vapor pressure. When you hit 70%, we start to see condensation form on surfaces. As soon as you have condensation, you have a risk of mold. I recommend never letting your dry room approach 70% humidity; in fact, even 65% is too risky. Condensation is a terrible thing in a dry room as it offers mold a space to thrive.  

Maintaining Optimal Conditions for Cannabis Drying

If our goal is “60°F at 60%,” we need to consider how we will achieve and maintain those conditions. To size equipment properly, you must determine your wet cannabis weight and dry cannabis weight. The final weight will be about 20-30% of the starting weight. Depending on strain and bud density, the final water content removed varies. 

We always strive to design the system to remove the maximum potential water content.  We need to remove 25% of the water content in each of the first two days, and then we need to slow down the remainder of the removal over 7-14 days. By happenstance, 60°F at 60% allows cannabis to remove a high moisture content in the first couple of days and not over-dry the crop in the remainder of the time. After day two, your equipment may remove too much moisture; in this case, you will need a humidifier. If you can not over-dry the space, then a humidifier isn’t required.

If we start with 120 pounds of product, we need to size the system to remove 24 pounds per day (120 pounds* 20% = 24 pounds per day). This means we need to remove a pound of moisture per hour. It’s essential to have a separate air conditioner and dehumidifier so you can set one for temperature and the other for humidity.

Remember, every time the air conditioning turns on, the moisture in the room will decrease. It’s vital not to oversize the air conditioning, or it will overdry the space when it turns on. In general, it’s best to size the system very close to your load in small rooms; oversizing or undersizing will cause you grief. In the first two days, I prefer to see the product dry a bit faster and not reach 70% RH, then take my time. Again, 70% is hazardous for mold growth and microbial development.

As with all HVAC systems, I recommend a quality building automation system, such as reliable controls, so you can customize your setup and maintain optimal conditions every time. All proprietary or “grow room” specific systems tend to be suitable for small-scale grows, but please don’t use these residential grow controls and expect to maintain perfect conditions.

Handy Tools to Dry Cannabis

Drying isn’t rocket science, but it does require some time and effort. I also recommend having a proper setup for curing available. In the past, we have used products like C-vault, which are stainless steel containers that require periodic burping. The modern version is a “grove bag” or similar that allows moisture to flow, but only at a defined rate.

Cannabis drying is the last and most crucial step in your grow. Don’t rush and abuse your flower out the door. Take your time and relax; you will be rewarded for your patience.