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How to Avoid Cannabis Mould

Q. What’s worse than having no cannabis?

A. Having mouldy cannabis, you can’t smoke.

Picture it – you have a nice bag stashed away, and you’re rubbing your hands with glee as you imagine that familiar mouth-watering aroma. You go for your stash and open it up, but instead of dank, it smells damp. You pull out a bud to inspect it, and the bud is covered in a tell-tale white powdery substance, but those aren’t trichomes glistening in the light – it’s mould. It’s the real weed killer. Your stash is ruined, and so is your weekend.

If you’re foolish enough to smoke it, your lungs are ruined, too. Mouldy weed can cause serious health problems, so whatever you do, if you spot mould, take the L and throw out the weed. Don’t try to knock the mould off, and don’t simply discard the mouldy bits and save the rest. It’s going to hurt, but the whole lot has to go – do not be tempted to risk your health.

Mould is a fungus that loves to settle on cannabis flower, and once it settles, it makes itself at home. With a bit of research, you could easily have avoided this. So what did you do wrong, and what could you have done differently? First, let’s address the problem of mouldy weed itself.

Types of Mould Found on Cannabis

The most common type of mould you’ll find growing on cannabis plants is Botrytis Cinerea – aka Bud Rot. This form of mould will appear on a plant as it grows rather than after harvest. Look for fuzzy, greyish-white hyphae on the colas – it’s unlikely that you would confuse these with trichomes, the glittery jewels that signify a good potent strain.

cannabis mould

After harvest, the villain of the piece is a type of mould called Aspergillus. The mould spores can cause significant problems once airborne, especially in people with weakened immune systems or any lung damage. When exposed to this, one could end up with an infection called Aspergillosis, which spreads through the lungs, kidneys, and brain and is typically fatal – this is why mouldy weed should be discarded and never smoked. If you obtain your cannabis from a dispensary, the experts there should test all Aspergillus products. If you don’t get your cannabis from a dispensary, you need to know how to spot mould on your weed to take action.

How to Tell if Cannabis is Mouldy

Thankfully, several giveaways let you know if your cannabis has succumbed to mould, so it’s up to you to regularly check on your weed to ensure it’s clean and safe for consumption. Mouldy cannabis can be identified visually and by smell, so look out for the following tell-tale signs of mould:

Tiny black dots on the buds – this typically indicates the early formation of mould.

Yellow, grey or brown fuzzy-looking growth – mould has your weed firmly in its grip.

Unpleasant odours – Some strains can be uber-pungent, of course, but if you detect a scent similar to sweat or urine, discard your cannabis immediately as these smells are indicative of mould.

Or, it’s pretty easy to spot:

cannabis mould

Whenever you look for signs of mould with the naked eye, always make sure you do so in a well-lit environment. Natural light can be deceptive, so it could be something as simple as using the torch on your phone to illuminate your buds. Whatever you use, make sure it’s a good strong source of light, and you can see all areas and colours present on the buds with a reasonable degree of clarity. Some even recommend using a magnifying glass to ensure you’re inspecting your cannabis as thoroughly as you can.

What Causes Mouldy Cannabis

Assuming your cannabis made it from the grow room to your fair hands and is free from mould, the growers have done their job correctly, and the problem has occurred at your end. Once the cannabis has been transferred from the cultivation room, things can get dicey. Most commonly, high humidity levels, light, temperature, air circulation and excess moisture are the things most likely to facilitate the formation of mould. So it’s essential you know a bit about the safe and proper containment and storage of your weed.

Mould loves moisture, warmth and stagnant air. If you’re in charge of your plants, the drying and curing process is vital in eliminating the precipitating factors that lead to mould growth on cannabis, so it’s crucial you take your time and don’t rush the process. Unless the cannabis is appropriately and thoroughly dried before being put into containers, you’ve given the mould a head start.

How to Store Weed to Prevent Cannabis Mould

Assuming your weed is properly dried and cured, now comes the next essential step in preventing mould – storage. The storage strategy you choose goes a long way to determining whether you keep mould at bay and how long your cannabis stays good.

You have numerous options here, but they’re not all good. Plastic bags, for instance, make for terrible cannabis storage conditions – even the sealable kind do nothing to protect your weed from air, heat, cold or moisture. Plastic bags are far more permeable than you may realise and will degrade cannabinoids quite quickly and diminish the potency of your nugs. If that’s not enough of a reason to avoid plastic bags for storing cannabis, these bags are prone to static electricity, which can pull precious trichomes away from the plant and onto the plastic, robbing you of some of the highly-prized sticky substances that make your cannabis fabulous.

You can buy specially-designed stash boxes for storing your weed. They’re typically airtight, smell-proof, waterproof and UV-proof, making them perfect for storing your buds. Even better, some of them come with bonus content like rolling trays and grinders and are a good investment, although they can be pricey.

These Seedsman Ziploc bags keep air out and smells in,are a cost-effective way to ensure small amounts of bud are kept fresh for longer.

Arguably the best way to store your weed at home is to keep it in a glass jar. Whether you buy jars for the purpose or simply re-appropriate old jam jars, coffee jars or whatever type of glass jar you can get your hands on, it doesn’t matter as long as there is an airtight lid and the jar is clean. Bonus points for you if you get a vacuum-seal top.

Why Store Cannabis in Glass

Glass jars are the ideal storage vessel for cannabis for several reasons. The long and the short of it is that they resist all the conditions that make mouldy weed possible:

  • Oxygen can’t permeate glass
  • Glass isn’t affected by residual humidity
  • If stored in the correct location, temperature fluctuation won’t affect the contents
  • No chemical secretions to damage your terpenes
  • Smell-proof
  • Buds may continue to cure and even gain potency over time
  • Glass mason jars are inexpensive and easily obtainable
cannabis mould

If you do choose to go with an old jar you’ve used for other purposes, clean it well and dry it thoroughly. In fact, scrap that – dry it surgically. If you have traces of moisture remaining in your jar when you come to fill it with cannabis, guess what? You’ve created the ideal breeding ground for mould. No matter how careful you are with outside factors (heat/light etc.), the damage is happening inside your container.

Where to Keep Your Cannabis Jars

This one is a relative no-brainer. You should keep your jars in a dark, dry place, away from sunlight and heat. A cupboard, closet, cabinet or drawer should do the trick, as long as it’s a good dark place and a dry environment. Don’t store your jars in the fridge or the freezer, as the moisture and temperature will damage your buds. Be aware that a clear glass jar will offer no protection against sunlight and heat damage. For that reason, it’s even better if you can get your hands on opaque or tinted jars for the purpose. Keep the environment temperature below 23C (mould thrives above 25C). Aim to keep the humidity in the high 50% to low 60% range. Going below this humidity range will help keep mould at bay, sure. But you’ll risk drying out your weed too much.

cannabis mould

Make Sure you use the Correct Size of Jar

Another consideration is the size of your jars. You don’t want to use a 16oz jar to store a small quantity of cannabis as you need to reduce air volume. Keep those jars packed nice and tight, and make sure they’re well-filled.

Label and Monitor

It’s a good idea to label each jar with the date you filled it and check in regularly to see how your weed is surviving. Cannabis buds begin to degrade after a few months, but this is dependent on strain and how it’s stored.

Humidity Control

You can call upon outside reinforcements to control humidity if needs be. Humidity packs are available for about the price of a decent cup of coffee. They can be placed inside the jar along with your cannabis. They will keep the humidity level inside the jar low enough to stop mould from growing. But high enough to prevent your weed from drying out and potentially losing flavour and potency. Humidity packs are a good option for short term and long-term storage. They can keep the relative humidity of the environment (jar, in this case) in balance.

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

Kyle Connolly