How To Prevent Bud Rot Organically

Bud rot is one of the outdoor growers’ worst enemies. It can happen indoors though it is much easier to prevent bud rot under a roof. However that sneaky fungus can destroy a whole outdoor patch in a matter of days.

What Is Bud Rot?

Also known as bunch rot or gray mold, bud rot is a term for a specific type of mold called Botrytis Cinera. This necrotrophic fungus not only affects cannabis but many other plant species as well. You may have already seen it on wine grapes or strawberries.

Botrytis has a incubation period of 18 to 30 days which means that when you start noticing it on your buds, it has actually been penetrating the plant’s tissues and building its mycelial network for quite some time already. The visible rot is just the tip of the iceberg. This is why you can prevent bud rot though treating it may feel like fighting a losing battle.

Botrytis on Outdoor Cannabis

What Can You Do About It?

There are a lot of chemical fungicides out there but we do not recommend spraying any chemicals on your buds. If you are using cannabis a medicine, it has to be as clean as possible.

Does it mean it is game over? Not quite yet!! In this blog post, we are not only going to give you some tips to prevent bud rot but we are also going to tell you about different organic methods that can slow down the spread and help salvage many of these precious buds.

The Main Causes Of Gray Mold

Botrytis is naturally present outdoors in most countries. The spores are everywhere but they only germinate and spread under certain conditions.

Botrytis needs moisture to thrive (above 50% humidity) and mild temperatures as it becomes more active when the temperature falls bellow 65°F/ 18°C .

A bad air circulation also highers the risk of getting grey mold.
The fungus favors dense buds because they trap more moisture and provide less air circulation than fluffy buds.

Gray Mold Indoors

Indoor bud molding, photo by Fiftyweed.

September, October = Crunch Time

Marijuana plants become more and more susceptible to mold as they ripen for 2 reasons:
1) The buds are denser towards the end of the season.
2) As the days get shorter, the temperature quickly drops and it also rains more frequently.

Botrytis causes the buds to rot from the inside and the rot then spreads outwards. That is why it is so difficult to spot it in its early stage.

The earlier you catch it, the higher your chances of slowing down the spread.

Preventing Bud Rot Indoors

Afghanica Cultivar With Bud Rot
Afghan Strains are very prone to bud rot.

Because it is near impossible to eradicate Botrytis once it sets in your marijuana buds, the best thing you can do is prevent it from happening.
This is easy to implement indoors since you can control your growing conditions. Simply resort to a powerful extractor, use oscillating fans to increase the air circulation and raise the grow-room temperature if it falls below 65°F/ 18°C at night.

If your residual humidity is still too high, using a dehumidifier will get the job done. It is most important to use the dehumidifier in the second half of the flowering cycle.

In addition to that, some varieties are particularly prone to Botrytis, even indoors. If controlling the RH, the temperature and maintaining a good airflow in your grow room is challenging, avoid growing certain mold-sensitive strains. For instance most afghan cultivars and Indica-dominant hybrids can easily mold because they originate from a very dry climate.

Preventing Botrytis Outdoors

Choose The Right Strains

Most modern hybrids have been bred indoors and are not the most suitable for outdoor cultivation. That can be an issue in cold climates such as northern Europe or parts of north America. Choosing the right variety is the single most important thing you can do to avoid a costly and tedious battle against bud rot further down the road. Prevent bud rot easily by opting for strains that have been bred specifically for their mold resistance and/or ability to finish early.

For instance, early finishing varieties such the Fraise Sativa or the Moroccan Beldia are usually ready before the end of the summer. Likewise, autoflowering strains can give great results in cold/wet climates.

Moroccan Landrace Finishing Outdoors In Mid August

Increase Air Circulation

Prune the bottom of your plants and spread the branches apart through a trellis in order to increase the air-flow. You could also defoliate leafy buds by taking a few leaves off your colas to increase the air circulation and light penetration. But don’t overdo it as it would weaken your plants.

Only Water In The Morning

Only water your plants in the morning to give the soil enough time to dry.

Beneficial Fungi

Certain beneficial fungi make it almost impossible for Botrytis to colonize a plant. Clonostachys rosea f. rosea, also known as Gliocladium roseum for instance, prevents Botrytis by blocking its ability to take up real estate.

Bordeaux Mixture

Bordeaux mixture is an old fashioned fungicide. Although it is 100% organic, you cannot spray it on your buds because Bordeaux mixture is a copper fungicide that will color your plants blue!!
You can easily make your own Bordeaux mixture by mixing 1 part builders’ lime with 1 part copper sulphate.

To apply, dissolve 1.2 ounce (35 grams) of mixture per gallon (3.8 liters) of water.

Spray some Bordeaux mixture early on, during the first couple of weeks of flowering. The mixture will not only protect your plants against Botrytis but also many other types of fungi.

Dew on Outdoor Bud

The morning dew can cause Botrytis to spread.


Milk contains beneficial lactic acid bacteria (LAB) and has certain antiseptic properties which makes it great at preventing fungal diseases.
Spray your plants in bright sun since you will need sunlight to activate these anti-fungal properties.

The recipe is fairly straight-forward. Mix 1 part organic milk with 2 parts water and spray your plants thoroughly with that solution.

Milk will make your plants smell funky for a few days so you should stop spraying it at least a  week before harvest.

How to spot Botrytis on your buds?

It is extremely hard to spot at first. However when the temperature starts getting cooler, when the dew is present every morning or when it rains on your plants, you know that you cannabis runs a greater risk of developing mold. Beware! It is time to inspect your plants every day.

Note that if a Botrytis infestation is too widespread on a plant, it is preferable to discard and throw away that plant. Bud rot can be a health hazard because some people are allergic to the spores.

Tell Tale Signs

In a very wet and cool climate it can be very tricky to prevent bud rot. This is why it is important to be able to spot Botrytis attacks early on. Look out for yellow or dead leaves.
When one or a small group of yellow leaves appear in the middle of your main colas, it is often the sign
of a Botrytis attack. Go ahead and pull these leaves. If they come off easily, it is another telltale sign. Spread these buds apart to look for the mold itself.
If it is moldy or slimy on the inside, it is now time to wage an all out war against this enemy!

Botrytis attack on outdoor plant, photo by Frankl1n

Treating Bud Rot

Remove all affected parts

As soon as you spot a patch of mold, remove the entire affected part using sterile tools. Snip off these moldy parts as gently as possible so as not to spread the spores onto the plant. Then, Put these in a trash bag and remove them from your grow location.

Baking Soda or Potassium Bicarbonate

Baking soda and Potassium Bicarbonate can help prevent bud rot and can also slow down its spread.

Bicarbonates or Baking Soda is a proven method to control powdery Mildew. Its high pH and buffering capacity are also effective against Botrytis Cinera.

To apply it, simply mix 2 to 3 table spoons of baking soda per 1 gallon (3.8 liters) of water. Add 3 drops of organic dish soap and 1 table spoon of vegetable oil. Then, shake well and spray it on your cannabis. Make sure to spray it on the buds and all the under leaves.

Baking Soda To Prevent Bud Rot

Milk Soda

Combine milk with baking soda for optimum results.

Bacillus Subtilis (Seranade)

Bacillus subtilis is a soil-dwelling bacterium that has the ability to control leaf blight, gray mold, black mold, powdery mildew and many other diseases. Compared to Bordeaux mixture, milk and baking soda Serenade is a bit on the expensive side. However, it is very effective in preventing bud rot and can help slow its progression. Serenade can be used in organic gardening.

What If It Spreads?

All these methods will help slow down the spread of Botrytis but they will not cure the affected plants as Botrytis is systemic. Most growers use the plants that are slightly affected for extractions. Because Botrytis Cinera can cause allergies, it is preferable to destroy the plants When the mold starts spreading. The best cure remains prevention.