Preventing Mold and Mildew in Beginner Grows

Growing cannabis can be a rewarding experience for both hobbyists and commercial cultivators alike. However, like any plant, cannabis can be susceptible to various pests and diseases. One of the most common issues, especially for those new to cultivation, is the presence of mold and mildew on plants. These fungi can significantly diminish the quality and yield of a crop, potentially rendering it unusable. This article aims to guide beginner growers on preventing mold and mildew in their cannabis grows.

Understanding Mold and Mildew

Mold and mildew are types of fungi that thrive in warm, moist environments. When they develop on cannabis, they can pose health risks to consumers and significantly reduce the crop’s market value.


Mold is a multicellular fungus that appears fuzzy and can be a variety of colors, including black, green, or white. The most infamous type of mold that affects cannabis is Botrytis, often called “bud rot.” It begins inside the bud and works its way out, making it particularly dangerous as it might not be visible until it has significantly infected the plant.


Mildew, on the other hand, is usually white or gray and has a powdery or fluffy appearance. Powdery mildew is a common threat to cannabis plants and can cover leaves, stems, and buds, impeding photosynthesis and overall plant health.

Conditions Favoring Growth

Understanding the conditions that mold and mildew favor can be the key to preventing their occurrence.


Both mold and mildew thrive in high humidity conditions. Cannabis plants, particularly in their flowering phase, can release a lot of moisture into the air, raising the relative humidity of the growing environment.

Poor Air Circulation

Stagnant air can allow moisture to settle on plant surfaces. This moisture can become a breeding ground for fungal spores if it doesn’t evaporate quickly.


While both mold and mildew can survive in a range of temperatures, they tend to prefer warmer conditions. However, sharp temperature fluctuations, especially when combined with high humidity, can be particularly problematic.

Preventative Measures

There are several steps growers can take to create an environment that’s unfriendly to mold and mildew:

Monitor and Control Humidity

Invest in a good quality hygrometer to regularly measure the relative humidity in the grow space. Aim to keep humidity levels below 50% during the flowering stage. Dehumidifiers can be employed to reduce excessive humidity, and humidifiers can be used if the environment becomes too dry.

Improve Air Circulation

Ensuring good airflow is crucial. This can be achieved by:

  • Using oscillating fans to keep air moving throughout the grow space.
  • Positioning fans so that they don’t blow directly onto plants to avoid stress or damage.
  • Regularly pruning plants to remove unnecessary growth and open up the canopy, allowing for better airflow.

Maintain Optimal Temperatures

Maintain a consistent temperature in the grow space, preferably between 68-77°F (20-25°C). Avoid letting the temperature drop dramatically during the dark cycle, as this can cause condensation on the plants.

Regular Inspections

Regularly inspect plants for signs of mold and mildew. This includes checking the undersides of leaves and inside dense buds. If any mold or mildew is spotted, it’s essential to address it immediately.

Treatment Options

If preventative measures fail, or if a grower notices mold or mildew in their grow space, quick action is essential.

Remove Infected Material

At the first sign of infection, remove the affected leaves or buds from the plant. When doing so, be sure to sanitize hands and tools afterward to prevent further spread.

Natural Remedies

Mild infestations might be treatable with natural remedies like neem oil, milk sprays, or baking soda solutions. However, these can alter the taste of the final product, so they should be used with caution.


For more severe infections, consider using a fungicide. Ensure that any products used are suitable for edible crops and always follow the manufacturer’s instructions.


Mold and mildew can be devastating for cannabis cultivators, but with knowledge and vigilance, their impact can be minimized or prevented altogether. By understanding the conditions in which these fungi thrive and actively working to prevent them, beginner growers can maximize their chances of a healthy and bountiful harvest.