Mould vs trichomes at a glance
Check these five things, ideally with a magnifier and good light.
- Shape: trichomes are tiny stalks topped with round heads 40 to 110 microns across, according to a 2023 Simon Fraser University study. Mould grows as a mycelium, a mass of branching threads, per Britannica, and can turn dusty or powdery as it produces spores.
- Colour: trichome heads turn from clear to cloudy white to amber or brown as they mature, the same study notes. Mould looks duller: Simon Fraser researchers who sampled licensed growing facilities in British Columbia found powdery mildew as a white coating and Botrytis bud rot as greyish-brown growth with brown, decaying tissue.
- Where it sits: trichomes cover the outside of the bud, including the tiny leaves around it. Powdery mildew starts on leaves as sparse white threads before turning powdery, and bud rot can grow inside the bud, where you can't see it from outside.
- Texture: resin makes trichome heads sticky, so healthy buds feel tacky and look sparkly. Mould looks fuzzy, webby or chalky.
- Smell: fresh buds smell like the strain. Musty odours signal damp, the condition mould needs, as the City of Toronto notes for homes.
How to check a bud with a magnifier
Glandular trichomes are distinctive enough that low-power microscopy is one way cannabis is positively identified, according to the European Union Drugs Agency. At home, a jeweller's loupe or a clip-on macro lens for a phone is enough to see them. Our guide to trichomes explains what they do and why they change colour.
- Use bright white light and look at the bud from several angles.
- Find a single trichome: a short stem with a ball-shaped head. Clear, cloudy and amber heads side by side are normal.
- Ignore the long orange-brown hairs. Those are the flower's stigmas (pistils), not mould.
- Look for anything without a head: thin threads bridging the gaps between bracts, fuzzy tufts or a flat white film.
- Break the bud open over white paper and check the centre. Grey-brown fuzz or brown, decaying tissue inside points to bud rot.
- Smell the broken bud. A musty, damp smell backs up what you see.
If it's mould, bin it
Mouldy cannabis is not worth trying to save.
- Don't smoke, vape or bake it. Most mould toxins are chemically stable and survive food processing, according to the World Health Organization, so cooking it into edibles is no fix either.
- Don't cut off the visible patch and keep the rest. The WHO notes mould can grow deep into food rather than only on the surface, and bud rot can already be inside the bud.
- Throw out the affected buds and inspect everything that shared the container.
- If you bought it, tell the seller or producer. Health Canada's consumer information sheet says you can also report concerns, complaints or adverse reactions about cannabis products to Health Canada.
Who faces the most risk
In its guidance on household mould, the City of Toronto says most common moulds are not harmful to healthy people, but those with weakened immune systems, allergies or chronic lung conditions are the most likely to be affected. A CDC study of U.S. insurance claims found people who used cannabis were 3.5 times as likely to have a fungal infection as people who didn't, though such infections were uncommon and the study could not show that cannabis caused them. If you have smoked something that may have been mouldy and feel unwell, talk to a doctor or pharmacist. Our guides on what to do with mouldy cannabis and the risks of smoking mouldy weed go further.
Keeping buds mould-free
Mould needs moisture. The WHO notes that mould usually doesn't grow on properly dried and stored food, and the same idea applies to buds: dry and cure them fully, store them airtight somewhere cool and dark, and never seal up buds that still feel damp. Our guides to drying and curing buds and storing weed cover the details.
Legal cannabis in Canada must be tested for microbial contaminants, lot by lot, under the Cannabis Regulations. That reflects the product when it was tested, not how it is kept afterwards, and the Simon Fraser team notes that Botrytis infection during growing can lead to losses later in storage.
Buying flower
GasDank's menu carries lab-tested products. Browse all flower for same-day delivery across Toronto and the GTA, usually within one to two hours, or mail order across Canada. Customers must be 19 or older (21 in Quebec), with ID checked at the door. Whoever you buy from, the magnifier check takes a minute.
