Here’s How To Protect Your Weed From Mold

Mold spores are everywhere, but we don’t want them in our weed! Here’s a handy guide to spotting, preventing, and dealing with mold in your herb.

May 25, 2016 - Christopher Teague

As with any fresh produce, there are two concerns when choosing cannabis: pesticides and mold. Pesticides can be controlled simply by ensuring that you, or the source you get it from, choose not to use harmful chemicals in growing or protecting their crop. Mold, on the other hand, is a product of the environment, and can sneak into herb at any stage without proper controls. Here is a handy guide to understanding, spotting, and preventing this lecherous growth from ruining your precious plants.

Why mold is bad

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For those who live in dry climates, mold is a rare concern, but for those who live in humid parts of the world, the devastation it can cause to houses and health is well known. When mold manages to get a foothold on herb intended for smoking, it can cause serious health complications. It is far more likely than getting laced weed, and its effects will often be mistaken for that more sinister culprit. It can cause, depending on the type of mold and exposure, a number of symptoms including:

  • Coughing
  • Trouble breathing
  • Headaches
  • Vomiting
  • Diahrrea
  • Heart palpitations
  • Pneumonitis – inflammation of the walls of the alveoli in the lungs
  • Aspergilloma – mold growth in the lungs

Luckily, mold can be easily detected and dealt with if you know what to look for.

Know thy enemy

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If it is in the early stage of growth, mold may be hard to notice with the naked eye. A discerning smoker’s best friend is a jeweler’s loop or 420 Scope. If it has spread, a blacklight will make it stand out in yellow to greenish-yellow. There are 5 main types of mold that affect cannabis: Aspergillus, Penicillium, Rhizopus, Mucor, and the devastating Botrytis.

  • Aspergillus:  A family of a few hundred molds, very common both indoors and out. You would be hard pressed not to inhale its spores on a daily basis. Their effects range from the smell in stinky shoes and food spoiling to lung diseases in animals and humans, especially those with compromised immune systems
  • Penicillium: Some species are used to create the antibiotic Penicillin and in the process of making cheese. Others can ruin fruit crops, or infect and harm animals and humans
  • Rhizopus: Widely found on fruits, jellies, bread, peanuts, and tobacco. Some species are opportunistic invaders of humans through infection including diabetic complications
  • Mucor: A fast growing mold that generally doesn’t affect warm-blooded creatures, a few species can cause rapidly spreading, necrotizing infections
  • Botrytis: Also known as bud rot or bunch rot, it is most infamously known for affecting grapes. The word literally means “grape disease”. There are two types of infection of plants. “Noble rot” or dry rot is actually used to enhance the flavor of some wines while gray rot” or wet rot is a devastating killer of crops of strawberries, tomatoes, rhubarb, and cannabis. It can infect lungs causing a condition called “winegrower’s lung” in predisposed individuals.

What to look for

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When looking for mold, whether under blacklight, a magnifying glass, or with the naked eye, there are common characteristics in the growth pattern and composition of most molds that will easily set them apart from the structure of cannabis buds. Just remember that those little hairs with shiny wet globs on them that cover the buds and upper leaves are the trichomes, where THC is produced. Those are the good guys.

Mold, on the other hand, will appear as:

  • Black spots or spores
  • White, grey, brown, or yellow fuzz
  • White, grey, or black web-like material, making it appear that bugs have made their home in the bud

The smell of mold can vary, so knowing what your herb is supposed to smell like is a plus. If it suddenly starts to smell musty, like urine, off-putting lavender, or that distinctive locker room odor, it is most likely infected with mold. There are some strains of cannabis that have odors described like lavender, cat piss, moldy cheese, or even skunks, but even on these strains, you can often tell the difference between an odor caused by the plant, and a foreign contaminant.

The causes of moldy buds

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Mold spores are all around us, and few places on earth can claim to be free of them, including most hospitals. HEPA filters, air tight rooms, and clean suits can prevent them from getting in, but are impractical. As long as you mitigate the causes of their proliferation, you can control the possibility of them hurting your herb, and you.

Molds like moisture and lack of air circulation. For grow rooms, fans act not only to strengthen stems, but to prevent insects from landing and molds from getting a foothold. Any grower worth his or her salt will make sure that they separate and discard any plants suspected of having mold before harvest.

Most mold actually starts after harvest. If moisture is too high in the drying process, mold will take hold. Some people like to use fruit peels to add moisture or flavor to buds that are too dry, inadvertently infecting them with spores from the fruit. Some less scrupulous growers or black market dealers might try to moisten weed to add weight, then store it in airtight containers, causing mold to occur. I have even known some people who would bury weed bricks in the backyard to “mature” them, intentionally causing mold in the false logic that it would increase potency.


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The moisture window for mold with cannabis is 55% for it to start to grow and spread. Any herb in conditions of at least 15% humidity could have spores land and survive, only to begin growth later. This is why both for curing buds and keeping your stash healthy at home, it is a wise course of action to invest in a hygrometer, like those used in humidors for cigars. Plastic baggies that never get opened are not the way to go.

When curing your buds, there are silica packets for keeping moisture levels down, test strips that can sit inside jars to warn of high moisture, and digital monitors for more accurate warnings. The most vital step in mold prevention besides moisture control is “burping” your containers. Make sure to infuse fresh air into the curing process often to prevent the stale breeding ground that molds love.

It’s too late, or is it?

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If you find that your crop or stash is infected with mold, it is always better to trash it than risk your health, but for the desperate, there are some steps you can take to minimize the risk of still using it.

  1. Bongs: Water filtration will reduce spore contaminants in smoke by about 15%
  2. Baking weed: 10 minutes at 200°F will kill most mold and spores, but it still will potentially put mold particulates in your lungs, and possibly make you sick
  3. Super Critical Extraction: Extracting your cannabinoids via butane or alcohol extraction will leave behind most of the mold, and is your best bet, especially if you vacuum purge at least 200°F overnight, killing any remaining spores. The higher temps used to dab conentrates will also help eliminate any stubborn survivors. This process, while your most thorough option, is still not 100% sure

Rest assured, dispensaries are way better than dealers, as they inspect any bud before putting it on shelves with microscopes and testing for the presence of contaminants, including mold. Another reason legalization is better for our health.

Have you ever been affected by moldy weed? What happened? Let us know on social media or in the comments below.

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