How to Get Rid of Mold on Weed Plants (3 Ways)

How to Get Rid of Mold on Weed Plants (3 Ways)

Ever noticed odd, fluffy growths or weird white powdery patches developing on your cannabis plants?

Hate to be the bearer of bad news, but that could very well be mold taking hold. And if it is, you need to take care of it immediately.

Mold is a nasty pathogenic fungus that can devastate a plant's roots, stems, leaves, and buds. If left unchecked, it can completely ruin an entire crop in just a matter of days.

It tends to pop up after heavy rainfall or periods of intense humidity. 

And if it isn't dealt with swiftly, all your hard work and effort cultivating and growing cannabis could be wasted. 

This article will cover how to properly identify, eliminate, and implement preventative measures to stop mold from ever becoming an issue in the first place.

How Mold Affects Cannabis Plants

Here's why mold on cannabis plants can feel so devastating.

Mold can seriously damage cannabis plants to the point that they're no longer safe for consumption.

And once it takes hold, it spreads rapidly, like wildfire.

What's more; the fungal spores thrive in the dense buds and high humidity of grow rooms, which means indoor grows are more susceptible.

Mold can quickly ravage entire plants and crops if not addressed immediately. And when a large crop is hit, the loss is even more disheartening. The grower's time, effort, and money are basically wasted.

Unfortunately, not much can be done to save infected plants. The most cost-effective approach is prevention, as mold is difficult to eliminate once established. Keeping conditions ideal to discourage mold formation is key. As is quick action.

Once you spot infected buds, you need to get rid of them ASAP.

How to Spot Mold on Weed Plants

The mold that affects cannabis plants can appear in different colors.

Some are white, some are brown, some are gray and fluffy, and so on.

Different kinds of mold can also affect cannabis differently, so it can be hard to tell right away that mold is the causing the problem. 

Thankfully, there are some clear indicators you can watch for.

  • White powdery patches on the leaves, stems, or buds. This is powdery mildew, a common cannabis mold. It spreads rapidly.
  • Brown or black spots on leaves or buds that may be slimy or crusty. This is indicative of botrytis - or bud rot.
  • Fluffy gray or green-gray growth on the soil or the plant's base. This is known as root rot and it's very deadly to plants.
  • Leaves yellowing, wilting, or looking sickly. These are symptoms caused by mold. Remember that mold may be present even with no visible growth.

During the flowering stage, trichomes can look like mold on buds - but don't be fooled. Trichomes are sparkly and separated. Mold is often fuzzier under a magnifying glass.

Keep in mind that you need to act fast when dealing with mold.

And remember that prevention is often more effective than cure. Check your cannabis plants thoroughly and often - especially in their moisture-prone areas like leaf undersides. Look for abnormal patches or textures. Inspect the soil around the plants regularly for mold.

You can trust your nose, too. Musty or rotten smells can indicate mold.

How to Get Rid of Mold on Weed Plants

Method 1: Pruning & Defoliation

Defoliation is when leaves fall off a plant, naturally or intentionally. In the case of mold, you would remove the plant's leaves intentionally. However, you also need to do this carefully. Defoliation can help reduce mold, but it can also hurt your yields.

If mold is limited to a few areas, you can try cutting off the infected leaves or buds. You can also remove some lower fan leaves and any dead matter to improve airflow and lower humidity. Dispose of these right away to prevent spreading. 

Alternatively, you can carefully prune lower growth as the plants mature. This will open up space and improve air circulation down below.

The goal of pruning and defoliation is to keep airflow good while maintaining healthy leaf coverage. This can prevent stagnant, humid pockets - where mold thrives - from forming. 

Method 2: Control Humidity & Air Circulation

Controlling humidity and air circulation is key to preventing mold on flowering cannabis. As we discussed in the previous section, strategic defoliation gets rid of infected areas and opens up airflow.

However, humidity and airflow themselves are the major factors influencing mold growth.

Keep humidity levels around 40%-50% to keep mold at bay. Use a dehumidifier and hygrometer to dial in the perfect levels. Proper ventilation also removes excess moisture. 

Position fans strategically around plants, making sure all areas get good airflow. Increase fan speeds too. This prevents stagnant, humid pockets where mold thrives. Optimizing airflow and controlling humidity keeps the environment dry to protect healthy, mold-free buds.

Method 3: Use Fungicides/Sprays

You can use preventative fungicides to keep mold at bay. There are some made specifically for cannabis plants. Here are some helpful tips for using these sprays:

  • Carefully read and follow all label instructions.
  • Wear protective gear like gloves and masks.
  • During flowering, spray the fungicide directly onto buds and leaves every 7-10 days.
  • After removing infected plant parts, disinfect the entire grow space to kill any leftover mold spores.

Aside from preventive fungicides and mold sprays, try applying a diluted bleach solution or commercial disinfectant to thoroughly sanitize all surfaces. This helps prevent future mold issues from returning.

Ideal Conditions to Prevent Mold

Prevention is the best cure for mold. If you can create and maintain a grow environment that strikes the right balance between humidity, temperature, ventilation, and watering practices, mold won't even have a chance to touch your plants. 

  1. Humidity. Keep humidity levels at around 40%-50%. A hygrometer can be used to monitor the environment's humidity levels. Make adjustments when necessary. You can also use a dehumidifier to remove excess moisture in the air, as excess moisture encourages mold growth.
  2. Temperature. Keep the temperatures around the 20°C - 24°C range. This helps discourage mold development.
  3. Ventilation. Good airflow is key to keeping mold at bay. Use fans or an AC unit to keep the grow area well-ventilated. This constant air movement stops moisture from building up. Keep plenty of space between plants and prune them regularly. Good air circulation between plants lessens the risk of stagnant pockets of humid air forming,
  4. Watering Practices. Be careful about overwatering. Pools of standing water raise the risk of mold and fungi forming. Water your weed plants only when they need it, and be sure to let the soil dry out properly between waterings.

Frequently Asked Questions

Is it safe to smoke moldy weed?

Not really. Smoking moldy weed probably won't kill you if you're healthy, but it's still not recommended.

Aside from possible nausea and/or coughing fits, your body could straight-up force you to expel it. Not life-threatening, maybe, but definitely unpleasant.

And if you're allergic to mold in any way, you run the risk of contracting inflamed lungs or sinuses. Symptoms include general pain, congestion, and wheezing.

For people with a weaker immune system or lung issues, inhaling smoke from moldy weed poses higher risks. The mold may carry fungi like Aspergillus or Cryptococcus. If these get in your system, they can cause serious - even life-threatening - infections in the lungs, brain, and/or nervous system.

So while it may not be a death sentence for most healthy folks, moldy marijuana still carries some risks. It's best to steer clear if you can.

Is root rot the same as mold?

Root rot, like bud rot, is caused by mold.

As the name implies, root rot affects the roots of cannabis plants.

It happens when there's a fungus gnat infestation in the soil or if the plants have been overwatered.

Since cannabis plant roots are buried underground, root rot can be tricky to deal with. Aside from the fact that it affects a part of the plant that's often hidden, root rot symptoms (like curled leaves or discoloration) can be mistaken for other issues, like nutrient deficiency.

So even experienced growers may not realize the rot has set in until it's too late to save the plant.

If you can see the roots of the plant, root rot is unmistakable. The roots are mushy to the touch and will have turned a sickly brown color.

Are there mold-resistant cannabis strains?

Sativa-dominant strains have a natural advantage when it comes to battling mold growth.

Their tall, airy structure promotes excellent air circulation around the buds, which helps prevent mold.

Just remember that sativa strains take longer to reach the flowering stage compared to other varieties. This extended flowering time can be an issue in regions with shorter growing seasons.

A smart compromise would be to opt for sativa-leaning hybrid strains. These maintain many of sativa's mold-resistant traits while flowering a bit quicker. Additionally, some strains are purposefully bred with enhanced mold resistance in mind, so checking the strain specifics can pay off.

We recommend looking into the seed's genetic lineage, too.

Strains from families like Kush, Skunk, or Haze, as well as descendants of classics like White Widow or Northern Lights, have gained reputations for being mold fighters. Choosing genetics with this mold-resistant pedigree can give your plants a headstart in fending off fungal issues.


You now have the basic knowledge to identify, prevent, and eliminate mold issues like powdery mildew, gray mold, and bud rot on your cannabis plants.

By following these tips, you can significantly reduce the risk of mold and ensure a healthy, successful crop - no more smoking moldy weed.

To make life even easier, consider getting mold-resistant strains. At WeedSeedExpress, our strains are specially cultivated for resilience against mold, even in less-than-ideal circumstances. And they also come with a 100% Germination Guarantee! Browse our Kush, Skunk, and Haze strains for high-quality cannabis seeds that can stand their ground against mold.