Cannabis is a consumable, and per the standard of such goods, its quality degrades over time. The moment that cannabis is harvested, that process begins. The speed at which degradation occurs, however, is highly dependent on several variables including light, humidity, temperature, oxygen, and storage method.
Light and Cannabis Shelf Life
Cannabis storage guide after storage guide will instruct consumers to place cannabis in a dark place, but research supporting this recommendation is surprisingly scarce. In fact, if such a guide does cite any evidence, it cites one study… from 1979.
The study found that cannabis exposure to UV during storage facilitated the degradation of THC to CBN, a cannabinoid that does not naturally occur within the plant and is purely a symptom of degradation. While psychoactive, CBN is much less potent than THC and causes a different sensation.
What remains unclear is how drastic THC/CBN degradation occurs and at what levels of light exposure. Anecdotal evidence suggests that any THC/CBN degradation due to UVB exposure is negligible.
The bottom line is that, although to what extent is unknown, light exposure can affect cannabis potency, so keeping your dried cannabis flowers in a dark location may prolong shelf life.
Humidity and Cannabis Flowers
Mold is more common and far more insidious than laced marijuana. Ingesting moldy pot can lead to a lot of nasty reactions including diarrhea, vomiting, respiratory difficulties, heart palpitations, headaches, pneumonitis, and, my personal favorite, aspergilloma (moldy lungs).
This is why humidity is such a big deal when it comes to marijuana quality. Laboratory studies indicate that cannabis is best stored between 59% and 63% relative humidity (RH). When flowers are stored in overly humid conditions, they become susceptible to mold. When humidity is too low, the flowers become brittle and dry resulting in detached trichomes and a harsher smoke.
Cannabis stored in proper humidity can last up to three years. But if the flowers are exposed to too much water, they can quickly become breeding grounds for mold and too dangerous to consume.
Temperature Affects Cannabis Shelf Life
In addition to humidity, mold and mildew love high temperatures (between 77 and 86 degrees Fahrenheit). But mold isn’t the only potential consequence of overheating cannabis;
Heat can degrade the cannabinoids and terpenes that give flowers their potency.
Despite the danger of heat, it isn’t a good idea to store cannabis in a refrigerator because the constant and opening and closing of refrigerators usually mean a significantly high humidity level and an even greater chance for mold. While some choose to store their cannabis in the freezer, this risks damaging the trichomes and consequently reducing potency.
Oxygen and Cannabis
Although inevitable, exposing cannabis to air can also decrease its shelf life. Every time a mason jar of cannabis is opened, it loses some of its flavor, scent, and potency. This is why properly stored cannabis will last longer than cannabis flowers sitting in the open air for an extended period of time.
How to Properly Store Cannabis
Now that you know the factors that influence the shelf life of cannabis flowers, you are better equipped to properly store them. Here are a few tips:
Store cannabis flowers in a cool, dry place. Although light degradation may be minimal, why lose THC potency at all? Keep your cannabis flowers in a location shielded from the light such as a closet. Since heat rises, avoid placing your cannabis above heat producing appliances like a stove. While it may be tempting to store your flowers in a fridge or freezer, remember that refrigerators are incredibly humid environments and freezers can damage the plant’s physical integrity. If the indoor temperature is between 65 and 75 degrees Fahrenheit, you’ll probably be fine keeping it in a closet or low cabinet.
Invest in a humidity-control packaging product. Since mold is such a common and dangerous threat, it may be a good idea to invest in a product like Boveda’s 2-way humidity control packets.
Keep flowers sealed in an airtight container. If you aren’t going to go with a special humidity-controlling product, try to keep your cannabis airtight for as long as possible. Glass mason jars work well, but make sure that you don’t pack your cannabis too tightly or leave too much space.
How can you know if your cannabis flowers are still viable?
Since the method of storage plays such a big role in the longevity of shelf life, you may have to do some careful investigating to ensure that the cannabis you want to consume is still fresh. Here’s how you can do that.
Start with the Source—If you’re growing your cannabis, you will know how recently your product has been harvested and what environmental factors it has been exposed to.
If you are purchasing your cannabis from a dispensary, it doesn’t hurt to ask how long a batch of cannabis has been sitting on the shelf. Take note of how budtenders retrieve cannabis from their storage. Do they use their hands, or do they use something more delicate like chop sticks? The way that the cannabis flowers are handled should give you insight into how in tact the trichomes may be.
Take a Closer Look—Do the flowers look brittle and old? Is mold visible? To check for mold, pull apart the bud and look for black spots, grey, brown, white, or yellow fuzz. If anything looks suspicious to you, ingesting the cannabis may not be worth it. Remember, mold can be dangerous, especially for consumers with compromised immune systems.
Sniff Test—If you notice a musty or urine like scent, you may have mold on your hands. If you smell chemicals, you may be detecting pesticides or some inorganic substance you probably don’t want to ingest.
If you don’t smell anything at all, the cannabis may have lost its potency.
Use Your Hands—How does the cannabis feel? Does it easily crumble? If so, it may be too dry. The trichomes, oils, and terpenes may be significantly reduced. If it feels moist, you may want to take a closer look for mold. The flowers should be dry, but springy and sticky.