Moldy Weed: How to Prevent Bud Rot on Cannabis Plant

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Every time you step into your drying room or garden, the last thing you want to see is mold taking over your beautiful marijuana plants or buds.

Mildew thrives in humid environments, and there are many types of mold – the most common being bud rot and powdery mildew. If you catch it early enough, though, don’t worry too much. You can still save your crop. This guide will go over how to prevent bud rot before it starts or gets rid of it if has already occurred

What Is Bud Rot?

Also known as Botrytis cinerea, bud rot is a form of mold that starts in the cannabis buds’ cores. It usually begins at the base of the stem, making it difficult to detect early on. Once it begins, bud rot gradually breaks down surrounding buds and spreads out through your garden. If you don’t find it quickly enough, spores will grow which can travel around your entire grow room or garden.

When bud rot sets in, it quickly destroys the surrounding buds and can spread throughout your entire garden.

If you notice bud rot in its early stages, it will be white and wispy. However, if the rot is grey and black, then the bud is already damaged too much to save. Once it has a soft and mushy consistency, it is no longer safe to use. Usually, gardeners try to remove the infected area and allow the rest of the cannabis plant to grow. But if the infection has spread too far, they have no choice but to remove the entire plant from their garden.

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Bud Rot Prevention #1 – In the Cannabis Garden

There is no question that preventing bud rot is better than trying to cure it. Once an infection occurs, you need to be lucky enough to spot it before it gets too far. Bud rot can be difficult to detect; therefore, it is better to put in extra time and effort upfront to take the necessary precautions. Bud rot thrives in the following environmental conditions:

  • Low to moderate temperatures
  • Stagnant air
  • High humidity

Choose an option that eliminates the possibility of one environmental factor existing for too long. Start by thinking about the kind of plant you’re raising. For example, Indicas come from drying out regions in Asia and have tightly clustered buds that make them more vulnerable to mold if you try to grow them humid locations. On the other hand, Sativas originally come from areas near the equator where it’s always humid, so they aren’t as prone developing mold spores.

Preventing Bud Rot Caused by Low-To-Moderate Temperatures

The first thing you should take into consideration is the temperature. Make sure that your plants are not exposed to daytime temperatures below 70 degrees Fahrenheit. They will grow best in temperatures of 55-60 degrees at night (or when the lights are off).

Preventing Bud Rot Caused by Stagnant Air

Avoid stagnant air by investing in a high-quality ventilation system. This will guarantee constant movement of air, which is essential for preventing health problems.

Preventing Bud Rot Caused by High Humidity Levels

The level of humidity your plant needs depends on the strain, but as a general rule, don’t expose any plants to more than 70% humidity in the vegetative stage. Some strains, like Granddaddy Purple, actually prefer a much lower level of around 50%. Remember to decrease the humidity even further during the flowering stage.

Many people don’t know this, but when you water your plants actually makes a big difference in the humidity levels. The best time to water your plants is in the morning because most of the water will evaporate during daylight hours. Conversely, if you only water at night, the humidity rises as temperatures fall overnight. If you think the humidity level in your grow room is unhealthy, invest in a dehumidifier.

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Preventing Bud Rot Outdoors

As a general precaution, we recommend growing marijuana in a greenhouse or indoors. However, if you do choose to grow your weed outdoors, be extra vigilant and take the necessary steps to protect your plants from bud rot. After heavy rainfall, check on your plants immediately and wick away any moisture that has collected on them. You can also shake each plant in the garden to remove excess water.

How to Prevent Bud Rot in Susceptible Cannabis Plants

In addition, other problems with the marijuana plants might cause bud rot:

  • Dense buds
  • Dense foliage
  • Weak immune system

Plant growth can be hindered by high humidity levels and poor ventilation. Cannabis plants, especially indica strains, are more susceptible to bud rot because of their short and thick growth habit. The most at-risk plants have many leaves and buds that block airflow and increase exposure to humid conditions.

You can prevent bud rot by pruning your plants carefully, or by using Low-Stress Training (LST) or High-Stress Training (HST) techniques. These methods both involve exposing the lower parts of the plant to more air and light. As a result, the plant will grow more evenly, with no specific areas more susceptible to bud rot.

Your plants will be more resistant to 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 approach!

Tea brewed from compost is an excellent way to manure cannabis plants. It’s more environmentally friendly and effective to buy locally-sourced compost, however, you can also add organic matter such as worm castings, kelp meal, molasses, and fish hydrolysate.

add nitrogen, phosphorus, and potassium to your crop. These essential nutrients help plants stay healthy and fight off infections. Other diverse nutrients like sulfur, calcium, copper, iron, and manganese are also necessary for plant health.

Treating Bud Rot

If your plants have bud rot, it may be too late. However, the first thing you need to do is figure out if the plant is worth saving. Unfortunately, once a plant contracted this disease, there is no cure and it cannot be eradicated. The only solution is to cut away the infected parts of the plant; however, even after taking this step, there remains a chance that it will spread throughout the rest of the plant.

If you’re cannabis plants become infected with bud rot, it could ruin your entire crop. Bud rot outdoors quickly spreads from plant to plant and creates mycelia in the soil. Indoors, it resides on surfaces like walls or floors until moved. To manage bud rot, use a biological spray designed for the purpose; these treatments will keep the condition at bay until harvest time but cannot kill it outright.

If you want to try and save an infected plant, move it to a room with warm temperatures and low humidity. Most importantly, keep it away from other plants so the bud rot doesn’t spread.

Bud Rot Prevention #2 – In the Drying Room

After you harvest your plants, they may still fall victim to bud rot. To avoid this, check the plant’s colas for mold before cutting them down. If any is present, remove the affected area and spray the rest of the plant with a biological solution to prevent further spread.

You will have the best crop if you harvest it during a dry spell, which can be difficult to do since most marijuana strains grown outdoors are ready to harvest in October. If you think it might rain again soon, go ahead and harvest your buds as long as they are ripe.


Don’t put the branches up straight away. By taking off the fan leaves and trimming the buds first, you’re immediately decreasing moisture in the drying room while improving airflow. The standard drying method is to hang the branches upside down from wire hangers–something that has been proven time and again to work extremely well when there’s space between each piece of weed.

The three most crucial factors you need to take into account are light, humidity and heat. To ensure your weed dries properly, hang it in a dark room at a temperature of 70 degrees. The ideal humidity level would be 50% or below. If you don’t have enough space, lay the branches flat on a large cardboard box. Check up on your weed regularly and turn it over at least once each day

If you spot mold in your cannabis, it’s important to take immediate action. Increase the temperature and decrease humidity to help prevent the spread of mold.

The drying process can seem to take forever, but it’s important to be patient. The THC in the weed converts as it dries, and the chlorophyll breaks down more slowly. If you dry your weed slowly, the buds will taste better and be more potent.

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


Your cannabis won’t reach its potential without being correctly cured. The process of curing helps eliminate any remaining moisture and further improves the quality of your marijuana. Once it is dry enough, put it in a glass mason jar and seal it tightly shut.

Check on your cannabis regularly and open the jar for a few minutes every day to allow moisture to escape the container. Do this for approximately one week, then return to opening the jar every few days.

Final Thoughts on How to Prevent Cannabis Plant Mold

Reducing the risk of bud rot should be a grower’s top priority. Although there are ways to treat bud rot, prevention is always better than cure. The best way to prevent bud rot is by keeping thegrow room temperature relatively high, reducing humidity and ensuring good ventilation. If plants have dense foliage or buds, prune and train them so that hidden areas are exposed to light and heat. When harvesting time comes around, make sure you follow the correct dryingand curing protocols to avoid any problems with bud rot.

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