It's every grower's nightmare: successfully germinating your seeds and watching them thrive, only to discover that your cannabis plants are covered in mold spores. This destructive pathogenic fungi, also known as 'bud rot' or 'Botrytis', can cause serious damage to a plant's roots, stems, leaves, and buds. Worst-case scenario, cannabis mold can even ruin your entire crop in a matter of days.
The growth of mold on weed plants can occur outdoors after heavy rainfall or indoors due to improper humidity levels, especially when buds are large and dense toward the end of the flowering stage.
It's important to detect and eliminate mold as soon as possible. Besides tasting bad and coughing excessively, smoking moldy weed can cause nausea and even induce vomiting. Besides the fact that nobody enjoys moldy weed, medical marijuana users have to be even more careful, as mold could seriously counteract the exact purpose you need it for.
In this article, we will discuss how to recognize mold on cannabis plants, how to spot it, and how to get rid of it. We will also discuss how to prevent mold from occurring in the first place.
What does mold look like on weed plants?
Learning how to properly identify mold on cannabis plants is important, as it can take on many different forms. Mold can be white, black, brown, or gray in color, but some common characteristics include:
White, powdery substance on the leaves, stems, and buds of the plant. This is a type of mold called powdery mildew, and it can spread quickly if left untreated.
Black or brown patches on the leaves and buds of the plant. These patches can be slimy or dry and crusty, and they are often a sign of a more serious type of mold called botrytis.
Gray or greenish-gray growth on the soil or on the base of the plant. This is often a type of mold called root rot, and it can kill the plant if it spreads too far.
How to spot mold on weed plants
Mold on marijuana plants can be difficult to spot, especially if you are not familiar with what it looks like. Keep an eye out for any changes in the plant's appearance or health. If the plant starts to yellow, wilt, or look sickly, it could be a sign that mold is present. Here are some tips for spotting mold:
Check the stems, buds, and cannabis plant leaves regularly. Look for any unusual growths or patches, and pay close attention to areas that are prone to moisture and humidity, such as the underside of the leaves.
Inspect the soil and the base of the plant. Look for any signs of mold, such as a gray or greenish-gray growth, or a musty smell.
During the end of the flowering season, your buds will likely be covered in trichomes. Due to their similarities in appearance, mold on trichomes is somewhat difficult to identify. Keep in mind that trichomes are sparkly, glistening, and thin resinous glands separated by minimal spaces. There are minute hairs with mushroom-like tips that look transparent or milky white. Mold, however, would look fuzzy, and dirty if you examined it under a microscope. You don't actually need a microscope, using a magnifying glass should suffice to determine the difference.
How to avoid mold on weed plants
Bad news first. To prevent mold entirely is something even the most advanced growers aren't able to do (just ask NASA). The good news? You can lower the chances of mold appearing significantly. The best way to prevent mold is to regularly check and adjust the conditions in your growing space.
Temperature and relative humidity (RH levels) are key factors when it comes to keeping your plants mold-free. A hygrometer (a device that measures humidity) can be a useful tool for maintaining the proper RH in your grow area. Aim for humidity levels of around 40-50% and try to keep your temperature between 20-24 °C to help prevent mold. It is not a rule of thumb that your plants will get mold if they grow outside of the ranges mentioned, but keep this as a guideline.
To avoid mold on marijuana plants, it is also important to keep your grow room well-ventilated and dry. A dehumidifier can help to remove excess moisture from the air, which can help to prevent mold growth. You can use fans or air conditioning to keep the grow area well-ventilated. This will help to reduce moisture and humidity, which are often the biggest culprits when it comes to mold growth.
Make sure the grow area is not too crowded. Overcrowding can cause moisture and humidity to build up, so it is important to have enough space between the plants to allow for good air circulation. Pruning the plants to allow for good airflow can help to prevent mold from forming on the leaves and buds.
Another important thing to remember is to avoid over-watering the plants. Excess stagnant water creates an ideal environment for fungi to flourish. Water the plants only when necessary, and be sure to let the soil dry out between watering.
How to get rid of mold on your weed plant
Despite your best efforts, you discovered you have moldy cannabis plants. Don't panic! If you act quickly, you can still prevent it from spreading. Please be advised that each type of mold may require a slightly different approach. So how do you get rid of mold?
Defoliation is one way. If your plants are large and leafy, you might need to remove some leaves. If the lower parts of your grow room aren't getting any (sun)light, odds are that neither are your plants. Make sure to also remove dead plant waste. Having less vegetative matter in the space will help to reduce humidity. Over-defoliating your plant, however, can dramatically reduce your yields. So solely use this method if your plant is very bushy.
Remove any infected parts of the plant. If the mold is limited to a few leaves or buds, you can try cutting them off and disposing of them. This can help to prevent the mold from spreading to other parts of the plant.
Increasing ventilation and airflow. Mold thrives in moist, humid environments, so increasing ventilation can help to dry out the plant and prevent mold from forming.
Humidity control is crucial! In other words, keep the plant dry. Water the plant only when necessary, and avoid over-watering. Also, make sure to water the plant at the base, rather than from above, to prevent moisture from accumulating on the leaves and buds.
There are many different fungicides available that are specifically designed to kill mold. Before using a fungicide, follow the instructions on the label carefully, and make sure to wear protective gear, such as gloves and a mask.
After removing the infected parts of the plant, it is important to disinfect the growing area to prevent the mold from returning. You can use a diluted bleach solution or a commercial disinfectant to kill any remaining mold spores.
What have we learned?
You now possess the basic knowledge to identify, prevent and eliminate mold on your cannabis plants. Whether you are setting up your grow space or are in need of treating powdery mildew, grey mold, or bud rot, on your marijuana plants. By following these tips, you can significantly reduce the risk of mold on your weed plants and ensure a healthy, successful crop and never have to smoke moldy weed.
Want to make life even easier? Then have a look at our section of Mold resistant strains, specially cultivated for extra resilience against mold and powdery mildew, even under less-than-ideal circumstances. Entirely new to growing and want to give your plants the best possible start? Check out our beginner's grow guide or visit our learning center, which is packed with a variety of other helpful articles about everything you need to know about cannabis cultivation.