How to Spot Mouldy Marijuana

byjeanmckinney5 minutes

Mouldy marijuana can smell bad and taste worse—and it can also make you pretty sick. Like any other plant, marijuana plants can fall victim to a vast array of moulds, fungi and bacteria. These unwelcome guests can appear at any point in the cycle of growing and harvesting the cannabis plant. They can also cause a variety of effects ranging from mild to life threatening, and they’re especially dangerous for people who use cannabis to treat a serious health condition.

Here’s how to recognize—and avoid—mould and other undesirable organisms in your marijuana.

Mould & Other Unwelcome Visitors in Your Cannabis Plant

Mould is an umbrella term that refers to various kinds of fungi that sprout from tiny spores that are carried on the air. This makes them just about impossible to avoid. So impossible, in fact, that a recent study by investigators at the University of California-Davis found potentially life-threatening fungi and bacteria in every sample of medical marijuana they tested.

Some fungi can be unsightly, but largely harmless to healthy people. However, other types that can infest marijuana can cause serious problems. This is especially true for people with compromised immune systems or respiratory conditions like tuberculosis or pneumonia. These mycotoxins include:

  • Cryptococcus, a fungus that poses particular danger to people with immune disorders
  • Mucor, which causes a variety of allergic reactions
  • Aspergillus, a family of fungi that affect the lungs

Along with fungi, marijuana can also contain numerous kinds of bacteria including E. coli and klebsiella pneumoniae.

How Does Mould Affect Marijuana?

Mould can develop in marijuana under a variety of circumstances. It can:

  • Exist in the soil where plants are grown, so that it turns the roots soft and rotten
  • Affect the stalks, leaves and buds of plants growing under improper conditions, such as excessive humidity or high temperatures
  • Also appear during the drying and curing process
  • Show up on dried buds that aren’t properly stored in airtight containers


How to Spot Mould on Growing Cannabis Plants

In most cases, mould is easy to spot on growing cannabis plants. Here are some of the telltale signs that mould is around:

  • Highly visible concentrations of white or grey powdery substances on leaves and stems
  • Fuzzy, grey or white hair on buds and flowers
  • Yellowed leaves
  • Smelly, slimy roots
  • Plants that simply don’t thrive—indicating mould in the soil
  • A musty or sour odor on leaves and buds

Sometimes, though, mould may not be so obvious. Cannabis plants with large, broad leaves may hide mouldy growth on the plant’s main stem. And a kind of mould called black rot infests marijuana buds from the inside, so that on the surface, they may look healthy.

Tips for Avoiding Mould on Your Home-Grown Marijuana

Because mould spores are airborne, it’s virtually impossible to avoid them entirely. But cannabis cultivators recommend:

  • Maintaining optimal growing conditions
  • Checking plants frequently for signs of mould
  • Discarding contaminated soil
  • Pruning back large leaves to make it easier to see mould growing close to the stem
  • Using mould-killing sprays or other products

But because the spores are microscopic, it can be virtually impossible to remove every one—and even invisible traces can be enough to cause illness in a vulnerable consumer.

Signs of Mould on Harvested Marijuana

When marijuana is dried and cured, or when it’s being stored for use, it can also develop mould of various kinds. When that happens, marijuana leaves and buds can have an unusual smell— musty, sweet or stale—depending on the kind of mould. It might also appear damp, with a grassy, wet scent. The dried buds may also develop a grey or white fuzz, or appear dusted with white powder.

The main reason harvested marijuana develops mould is dampness. If it’s improperly dried and cured, or stored in porous containers, moisture can provide a fertile ground for opportunistic spores. To reduce the risk of mould forming, keep harvested marijuana in an airtight container. Open it occasionally to allow fresh air to circulate.

It’s also wise to avoid smoking or consuming any cannabis that has gotten wet or that doesn’t smell fresh. Buds can appear perfectly healthy, but contain mould inside, so you may want to cut or break one open to check before consuming it. There isn’t an effective way to get rid of mould on cannabis. So if you do find mould, it’s probably best to toss it all out—and that includes any apparently normal-looking or smelling marijuana that the mouldy portion had contact with.

Symptoms of Mould-Borne Illness From Contaminated Cannabis

The greatest risk posed by consuming contaminated cannabis comes with smoking or vaping. But edibles also pose a danger since cooking even at high temperatures may not be enough to destroy moulds or the toxins they produce. And it’s even possible to ingest invisible mould spores on cannabis that appears perfectly healthy.

So, if you do happen to consume mouldy marijuana, what happens? Mould can cause a variety of allergic reactions in many healthy people, including:

  • Eye inflammation
  • Itchiness in the throat or mouth
  • Nosebleeds
  • Headaches
  • Chest pain
  • Dizziness
  • Fever
  • General malaise

But moulds, especially the very common Aspergillus, can also cause serious respiratory problems in people who already have a compromised immune system. Mould- borne illnesses can be especially risky for those with impaired lung function from ailments like chronic obstructive pulmonary disease, asthma, pneumonia or tuberculosis. That’s because when marijuana is inhaled through smoking or vaping, it goes directly to the lungs and from there to the bloodstream. In this way, mould spores can lodge in the tissues of the lungs or pass into other parts of the body.

How to Avoid Mouldy Marijuana

Mould can affect marijuana at every point in the growing and harvesting process, and even the most careful consumer can run across a bad batch. Buying from a licensed producer can help vulnerable consumers avoid the risks, because these facilities can use sophisticated processing to sterilize the marijuana products they produce. In any case, though, it’s important to stay alert, store your cannabis carefully and thoroughly examine any marijuana you use for obvious signs of mould.

Photo credit: tanjila ahmed