mould on cannabis

Peventing Mould On Cannabis

Few things are as disappointing as discovering your cannabis plants or weed stash is infested with mould. These fungal infections can occur in living plants as well as in cannabis harvests stored without proper drying or hygiene. Fortunately, there are ways to prevent such disappointment. This blog identifies several types of mould, as well as explaining how to keep mould on cannabis away from your grows.

How To Spot Mouldy Plants And Buds

Mould on cannabis plants or a stash of dried buds can really ruin your grow. It gets worse, though: mouldy weed can even damage your health. That makes it extra important to regularly check your weed for fungus problems and make sure it’s still safe for consumption. Doing so is a matter of using your eyes and nose. These are the main symptoms indicating mould on cannabis:

Tiny black specks on the flower buds are often early signs of mould;

Yellow, brown, or grey spots that appear ‘fluffy’ indicate advanced mould problems;

Check for unpleasant smell. Plants with fungal issues tend to stink, making them easy to detect by scent. If your weed suddenly starts to smell like sweat or urine, you know it’s time to get rid of it, pronto.

Checking for signs of mould on cannabis plants works best in well-lit environments. Natural daylight is not necessarily optimal; your phone’s flashlight is a nice and bright source of light, but a well-lit room is a good alternative. Make sure you can detect all the colours of the regular spectrum and take the time to thoroughly inspect your buds from all sides. Many people use lenses to literally get a closer look.

If you happen to discover mould on your cannabis, toss it away without hesitation. We hear you wondering: “Really? ALL of it?? Surely, that’s a bit drastic, isn’t it?” Well, we’re sorry, but it’s not. Consuming mouldy weed is a very real health hazard. Don’t think you can wipe off that mould, or just cut away the mouldy bits. Once you see mould appear on the surface of a bud, you can safely assume that the fungus has spread all through the flower and beyond, even if you can’t see it. Don’t risk your health over a few grammes of weed!

mould bud rot cannabis
Bud rot or botrytis.

Common Types Of Mould On Cannabis

There are three kinds of fungi that cause most of the problems associated with mould on cannabis.

Bud Rot (Botrytis cinerea)

Bud rot is the most common fungal infection found on cannabis. It is more likely to occur in the flowering phase than after the harvest. The process usually proceeds from the inside of the bud towards the exterior.


Aspergillus, in contrast to botrytis, usually sets in after harvesting the flowers. Airborne spores can cause serious health problems, particularly for those with weakened immune systems. This fungus can cause a condition called aspergillosis, which can spread from the lungs to the kidneys and brain. It is a rare condition, but nonetheless, aspergillus is one of the main reasons to never consume mouldy cannabis.

Powdery Mildew

Mildew is a fast-spreading fungus. Infections can start on any part of the plant, including the leaves as well as branches and stems. Plants wither and die wherever mildew spreads. Plants affected by powdery mildew appear as though covered in talcum powder, featuring white powdery clusters of mould. If you act fast, you have a chance of stopping mildew infections, but if the mould has spread too far, affected plants are usually doomed – and in all likelihood, so are their neighbours.

mildew mould on cannabis
Powdery mildew.

What Causes Mould On Cannabis

If you want to steer clear of discovering mould on cannabis plants, you need to be careful throughout the entire grow, from germination to growth and from flowering until after the harvest. Mould loves warmth, moisture, and stagnant air. Knowing this, there is much that growers can do to keep their plants and buds fungus-free.

Preventing Mould On Cannabis Indoors

Growing cannabis indoors calls for close monitoring of air humidity and circulation. A hygrometer is a useful tool for measuring humidity. Roughly speaking, the following relative air humidity levels are recommended for avoiding mould on cannabis indoors:

Vegetative stage: 50 – 75% (aim for 60%)

Flowering stage: 45 – 60% (aim for 50%)

Ensure proper air circulation. You can use fans for this, but directing the growth of your plants with techniques such as supercropping can be helpful, too.

A dense foliage canopy increases the likelihood of high air humidity and restricted air circulation. This is why strategic pruning and defoliating plants can help prevent mould on cannabis. Moreover, strong, healthy plants are more resilient to mould. Providing your plants with the right nutrients can help boost their natural immune system.

After the flowering phase, trimming, drying, and curing methods can also affect the chances of discovering mould on cannabis buds. Generally speaking, high humidity, air leaks, and temperature are the main culprits.

indoor mould prevention weed

Ultimately, however,  hygiene is the key to preventing mould on cannabis indoors. Always try to work as cleanly as possible, and be aware of how easy it is to bring fungi inside. If you have multiple tents or grow rooms, the last thing you want is cross-contamination by (invisible) fungal spores sticking to your clothes and fingers, or just drifting in through the air.

Make sure to clean any grow rooms thoroughly after every grow, and let in plenty of fresh air before starting up a new batch. Proper hygiene is often largely a matter of discipline, so making a habit of working neatly will go a long way towards avoiding mould on cannabis.

Avoiding Mould On Cannabis Outdoors

For outdoor growers, moisture is the main risk factor, usually in the form of rain (drizzle) or mist and fog. Such weather is most likely to set in during the final stages of flowering. By that time, the outdoor cannabis season is drawing to a close in large parts of the world, depending on the year’s weather conditions. At this point, bigger, denser buds become the perfect habitat for all sorts of fungi. This blogs explains how to protect your flowers from mould in the last weeks before the harvest.

water air circulation outdoor weed grow
Moisture is always a risk.

The Best Way To Preserve Cannabis

Once you have managed to dry your harvest without contracting mould on your buds, the next step is storing and preserving your weed. Here too, mould can ruin the eventual yield. Luckily, there are various storage techniques that help prevent mould on cannabis nugs.

Plastic Bags

If you are used to store your stash in plastic bags, we advise you to reconsider. Neither regular plastic bags nor zip-lock baggies will protect your weed from heat, cold, or moisture. These baggies are not as secure as you may think. Moisture and high temperatures render your precious buds vulnerable to fungal infection. Moreover, the quality of your stash will fade fast in these bags, as the cannabinoids soon start to deteriorate.

Stash Boxes

You can get purpose-designed stash boxes or similar containers that are airtight and waterproof while blocking UV light. These are a great option for stashing your cannabis flower.

Cannabis mould protection
Classic mason jar – regular burping required!

Glass (Mason) Jars

Another alternative comes in the form of glass jars. Whether you prefer classic mason jars or sterilised jam jars put to a new use, glass comes with a number of advantages over plastic containers. You will have to make sure that any jar you use can be sealed with an airtight lid, after thorough cleaning and drying of course. What makes glass containers so particularly useful is their inertia: the glass will not interact with the flower inside (contrary to many types of plastic), setting the perfect conditions for stashing weed inside.

There are added benefits to glass: if you put your jars in a safe place, temperatures will remain stable while keeping air and moisture out and without risking chemical reactions that affect the contents. A good jar will even allow your buds to continue curing as you stash them, further increasing the potency and flavour.

Once your harvest is stashed snugly inside your jars, make sure you find a dry, dark place to store them. Remember that glass jars do not block the light; don’t put them out in direct sunlight. Keep temperatures below 23°C at all times and make sure air humidity remains between 50 and 60%. You can add silica moisture traps to the stashed buds to catch off any remaining moisture if you like.

The Best Genetics Against Mould On Cannabis

Mould is a constant threat hovering over everything that growers and other cannabis lovers do. Fortunately, you now have the right information to protect your harvest and your stash against fungal infections.

wietzaadjes zonder schimmel

Of course, there is one other factor that helps prevent mould on cannabis no matter what the conditions: working with premium genetics! Professional breeders have spent decades developing modern strains with high mould resistance, so use their hard work to your advantage!

Only choose seeds suppliers with their own collection of high-quality strains, and read the product descriptions to find the ones with the best antifungal properties. In case you’re still in doubt, let us assure you that ordering your cannabis seeds at Amsterdam Genetics is a fine first step towards keeping your cannabis free from mould!

Pick Your Mould-Resistant Strains

All things considered, the war against mould will always be an integral part of the grower’s hobby. After all, we are working with nature here, and fungi are an ancient, respectable, and unavoidable part of any ecosystem – including grow tents and gardens. Nonetheless, the tips in this blog will help you protect your own plants as they grow and the harvest they produce, so pick that strain and let’s get growing!

2023 super silver haze amsterdam geneticssuper silver haze

Super Silver Haze