Bud Rot: How to Prevent Cannabis Plant Mold

Whenever you walk into your drying room or garden, you look forward to seeing your beautiful marijuana plants or buds. However, it’s not uncommon for you to one day check on your plants and find mold developing!

The trouble with mold is that it’s always ready to attack and thrive in the right conditions. Although there are numerous mold varieties, the most common are bud rot and powdery mildew. While it is disheartening to see an infection, don’t panic. If you catch it in time, you should be able to salvage your crop. In this guide, we focus on preventing and eradicating bud rot.

What Is Bud Rot?

Also known as Botrytis cinerea, bud rot is a form of mold that begins in the cores of cannabis buds. It tends to begin at the base of the stem, which means it is notoriously difficult to detect early on. Once it begins, bud rot starts breaking down the surrounding bud and spreading all over the garden. If you don’t uncover it quickly enough, it produces spores capable of traveling around your garden or indoor grow room.

Once it begins, bud rot starts breaking down the surrounding bud and spreads out all over the garden.

Bud rot is in its early stages if it is white and wispy. Unfortunately, if the rot is grey and black, the bud is already damaged beyond repair. Once it has a soft and mushy consistency, it is unsafe for use. Usually, gardeners try to remove the infected area and allow the rest of the cannabis plant to grow. Alas, once the infection has spread, you have no choice but to remove the plant from the garden.

Bud Rot Prevention #1 – In the Cannabis Garden

There is no question that prevention is better than cure when it comes to protecting your weed from bud rot. Once an infection has taken place, you need to be fortunate enough to spot it before it gets too far. It’s difficult to detect; therefore, it is better to put in extra time and effort to take the necessary precautions. Bud rot thrives in the following environmental conditions:


  • Low to moderate temperatures
  • Stagnant air
  • High humidity

The best option is to ensure that no single condition exists for a prolonged period of time. First of all, consider the type of strain you’re growing. Indicas come from harsh environments in Asia. Therefore, they have dense buds ideal for mold growth once you try to grow them in a humid climate. Sativas come from humid conditions close to the equator, meaning they are less likely to develop mold.

Preventing Bud Rot Caused by Low-To-Moderate Temperatures

Low-to-moderate temperatures are the first point of concern. Therefore, make sure your plants are not exposed to daytime temperatures below 70 degrees Fahrenheit. Preferably, they will grow in temperatures of 55-60 degrees at night (or when the lights are off).

Preventing Bud Rot Caused by Stagnant Air

The next problem relates to stagnant air. You can easily avoid this issue by investing in a high-quality ventilation system, as this will guarantee constant air movement.

Preventing Bud Rot Caused by High Humidity Levels

As for humidity, it depends on the strain. However, you should not expose plants to anything above 70% in the vegetative stage. Strains like Granddaddy Purple prefer a much lower humidity level of around 50%. Be sure to decrease the humidity in the flowering stage.

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Believe it or not, the timing of watering has a significant role in humidity levels. It is best to water your plants in the morning because most of the water evaporates during the day. If you only water at night, the humidity rises as the temperature falls. Invest in a dehumidifier if you believe the humidity level in the grow room is too high.

Preventing Bud Rot Outdoors

If you grow your weed outdoors, you must be especially vigilant. We recommend growing marijuana in a greenhouse or indoors because you increase the risk of bud rot with outdoor growth. If you grow outside, get ready to act after heavy rainfall. Make sure you wick the moisture off the plants as soon as possible. Alternatively, shake every plant in the garden.

How to Prevent Bud Rot in Susceptible Cannabis Plants

Some issues with the marijuana plants themselves could result in bud rot:

  • Dense buds
  • Dense foliage
  • Weak immune system

Even if you set your humidity levels to the ideal level and use an excellent ventilation system, extremely dense plants are still susceptible to bud rot. Once again, indica plants are at greater risk because they tend to grow short and thick. Plants with many leaves and buds will be exposed to a greater degree of humidity and poor airflow.

You can alleviate the problem by pruning your plants effectively. Another option is to use Low-Stress Training (LST) or High-Stress Training (HST) techniques. Both tactics involve exposing the lower parts of the plant to air and light. As a result, the plant grows more evenly, and there are no areas more prone to bud rot than others.

Your plants are less likely to contract bud rot if they have healthy immune systems.

It is also a fact that your plants are less likely to contract bud rot if they have healthy immune systems. Marijuana has been grown organically for thousands of years, so there is no reason to change a winning formula!

Compost tea is a fantastic addition to any cannabis garden. Make things easier by purchasing locally sourced compost and adding organic material such as worm castings, kelp, molasses, and fish hydrolysate.

Add essential nutrients like nitrogen, phosphorus, and potassium to your crop. Plants need other diverse nutrients, like sulfur, calcium, copper, iron, and manganese. These nutrients help to keep them healthy and ready to fight off infections.

Treating Bud Rot

Unfortunately, you may have already read this guide too late. If your plants already have bud rot, you have to find out how to treat them. Your first step is to decide if the plant is savable. Once a plant is infected, the disease cannot be eradicated. You can cut away the plant’s infected parts, but there is a risk of it spreading regardless.

If a bud rot infection sets into your growing room or cannabis garden, it can ruin your entire crop. Outdoors, bud rot quickly moves from plant to plant and reproduces in the soil as mycelia. Indoors, it sits on walls, floors, and practically any surface until you move it. To treat bud rot, use a biological spray designed for the purpose. Such sprays treat the condition and keep it at bay until harvesting time, but they won’t kill it.

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If you want to persist with an infected plant, move it to a warm room with very low humidity. Most importantly, please keep it away from other plants to prevent the bud rot from spreading.

Bud Rot Prevention #2 – In the Drying Room

If you think your plants are free from the threat of bud rot after harvesting, think again! Unfortunately, your plants can still be afflicted by the curse of mold when you dry and cure them.

When it’s time to harvest, check the plant’s colas for rot before you cut them down. If you find mold, remove the affected area. Next, spray the rest of the plant with a biological spray to prevent the mold from spreading.

Ideally, you will harvest your crop during a dry spell. It isn’t easy to do this because most marijuana strains grown outdoors are ready to harvest in October. If you feel it is about to rain again, harvest your buds ASAP, as long as they are ready, of course.


Don’t hang the branches up right away. By removing fan leaves and trimming the buds first, you immediately reduce moisture in the drying room while increasing the airflow. The classic drying method is to hang the branches upside down from wire hangers. It is a tried-and-tested tactic that works incredibly well when you leave space between the weed.

The most important factors to consider are light, humidity, and heat. Make sure you hang your drying weed in a darkened room at a temperature of around 70 degrees. Ideally, the humidity level will be at 50% or below. If you don’t have a lot of space, you can lay the branches flat in a large cardboard box. Check the weed regularly and turn it over at least once a day. If you haven’t bought a hygrometer to measure humidity already, now is the time to do so.

If you spot mold in the cannabis, increase the temperature and decrease humidity immediately.

The drying process can take much longer than you originally anticipated. It can take five to six days, but sometimes it can take as long as nine days! The most important thing is to be patient. The THCA in the weed is converting as it dries, and the chlorophyll is still breaking down. If you dry slowly, the buds generally have a better taste and increased potency.

However, if you spot mold in the cannabis, increase the temperature and decrease humidity immediately to speed things up and save your weed.


Your cannabis is not truly ready until it has been correctly cured. Curing helps remove all excess moisture and further enhances the quality of the marijuana. Once it is dry enough, place it in a glass mason jar, which you must then seal.

Check the cannabis regularly and open the jar once a day for a few minutes to allow moisture to leave the container. Do this for around a week and then revert to opening the jar every few days.

Final Thoughts on How to Prevent Cannabis Plant Mold

Overall, bud rot is a clear and present danger to your plants, and you are better off focusing on prevention. Keep the temperature in the grow room relatively high, reduce the humidity, and make sure the room is well-ventilated. If the plants have dense foliage or buds, prune and train them to expose the hidden areas to light and heat. Once your bud is ready for harvesting, follow the correct drying and curing protocols to avoid bud rot.

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