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Preventing Mold While Growing Cannabis

Updated August 21, 2022

If you grow cannabis, you want to grow the plant, not mold. Unfortunately, this can be easier said than done, especially if you are not sure how to avoid mold or excess moisture in your grow space.

The following tips will apply to growing cannabis both indoors and outdoors, but some make more sense in certain spaces than in others.

Moisture Control Is Crucial

As you look at the various methods of preventing mold while growing cannabis, you will notice that moisture holds a very important role. In most cases, the key to preventing mold is to ensure that you do not expose your grow space to excess moisture. Of course, there is more to it than this, but keeping that goal in mind will put you on the right foot.

Understand It Can Happen at Anytime

The other thing that you should keep in mind as you plan how to deal with mold is that this harmful and unwanted substance can appear at any stage of the growing process. You may get moldy seeds if you are not careful when germinating or may notice mold during the vegetative or flowering stage. Because mold can happen at any point, you need to keep your eyes out for it at all times and take the recommended steps throughout the growing process.

Remember Trichomes Are Also White

If you think that your cannabis has mold, keep in mind that this is not the only reason for the fuzziness in the right color range to appear on your plants. The buds should have trichomes, which are what give the cannabis the potency. If you are new to growing cannabis and unsure whether you are dealing with trichomes or mold, look at some example pictures. After growing cannabis for a bit, or even smoking it for a while, you should be familiar enough with the appearance of trichomes to recognize them.

Types of Mold and Unique Considerations for Each

To those unfamiliar with growing cannabis or other plants, all molds are the same. In reality, there are a few different types that you will have to contend with as you grow marijuana. While all share common features, they are also unique enough to have their own considerations and techniques for prevention and treatment.

Bud Rot

As the name implies, bud rot refers to mold that affects the buds. Bud rot is the most common cause of darker spots on the buds, but it will change appearance as it progresses. New bud rot begins as fluffy white mold. As it advances, you will notice dark gray, brown, or purple spots appear. When it becomes advanced, there will be speckled dust on the buds. This dust can be blown away, but the wind will not eliminate all of it.

To eliminate bud rot successfully, you will need to remove the bud from the stem completely. In some cases, you may also have to remove the buds nearby.

Bud rot is more common when there is not enough air circulation, low temperatures, or high humidity. As such, you can prevent each of these things to reduce the risk of bud rot. To keep air moving and prevent a lack of circulation, keep a fan running. To avoid low temperatures, keep the temperature in your grow space at a minimum of 20 degrees Celsius or 68 Fahrenheit. To avoid the extra moisture from high humidity, place a humidity monitor in the space, so the levels are low as you grow and harvest.

Fuzzy White Mold

You may also notice normal mold, which appears fuzzy and white. This is the type of mold that you are most likely to see growing on cannabis, and it is the most common on the leaves. This type of mold can, unfortunately, spread as the air circulates, so be careful and control it right away. In terms of appearance, the white, fuzzy nature of this mold means that it somewhat resembles the web of an insect.

Prevention of this type of mold just comes down to mold prevention basics: ensuring the appropriate climate for the cannabis. Start by ensuring your humidity levels stay around 15 percent, with an absolute maximum of 20 percent.

Keep in mind that if you notice white fuzzy mold on your plant, you will need to harvest it immediately, regardless of its current growth stage. You may even need to harvest the plants around it, as well. Doing this will prevent the mold from spreading.

Powdery Mold Resembling Mildew

The other type of mold you may spot on your cannabis plant is powdery and looks like mildew. It appears as if someone dusted flour over your plant’s leaves.

Keep in mind that this type of mold can spread incredibly quickly, eating plants to produce even more mildew. As such, if you do not take action right away, you are likely to lose most of your plants. If you catch it quickly, you can still save the rest of the crop and maybe even the plant affected.

The best way to prevent this powdery mildew is to control the humidity levels in your grow space. This may include buying a dehumidifier, depending on where you live. You will also want to minimize the airflow if you notice powdery mildew as that will limit its ability to spread. If you do not see any signs of mold, however, ensure there are good airflow and ventilation.

This type of mold is also more likely to develop and spread if the leaves of various cannabis plants touch. Overlapping leaves lead to increased moisture, which increases the risk of mold.

Regardless of the type of mold that you want to prevent on your cannabis plants, there are a few common tips to keep in mind.

Control Water and Humidity

The most clear-cut rule to prevent mold while growing cannabis is to control the level of humidity and the presence of water. Do not allow standing water in your grow space, whether in pots, on the floor, on top of the soil, or even in pans that catch excess water. Standing water will only increase the humidity level. At the same time, make sure you invest in a humidity monitor and consider getting a dehumidifier, as well.

A key element of this is to make sure you avoid overwatering your plants. Overwatering leads to excess dampness in and around the plant, which mold sees as an invitation.

Control the Temperature

You also need to be careful about the temperature in your grow space, always opting for coolness. Letting the temperatures in the growing space rise too high will encourage mold. Maintain the same type of temperature control in the areas you use for curing and storage as you do not want mold to attach itself to your cannabis at the end of all your hard work.

Avoid Certain Treatments

Those with experience growing cannabis will also typically suggest that you avoid certain types of treatments that could encourage mold. For example, avoid foliar sprays and treatments as these will add moisture to the part of your cannabis plant that needs it the least. Yes, the treatments were likely designed to do something positive, but your plant is unlikely to need them, and they could increase the moisture level. As an added concern, many chemicals could negatively interact with the internal chemistry of cannabis. Or, trace amounts of the chemicals could remain on the cannabis you consume, which you definitely do not want.

You also want to be wary about introducing fertilizer to your cannabis. Most cannabis should not require fertilizer at all in order to grow and be healthy. Most people who add fertilizer to their cannabis do so to increase the yield, but this will reduce the quality. It can also add moisture to the plant and soil, causing mold problems.

Ensure Proper Ventilation

One of the most important tips for preventing mold on your cannabis is to ensure that the room has enough airflow. This is much easier to achieve outside as nature typically provides the airflow. Inside, however, it becomes crucial, and you are in complete control. You will need to install a ventilation or fan system of some sort to prevent stagnant air.

The airflow will help dry out any moisture that lingers on the surface of the plants. It can also help with the part of photosynthesis involving gas exchange.

Ensuring proper ventilation also includes more than just setting up a fan or another system. You should also ensure that the lower leaves of your plants get enough airflow by trimming away any excess vegetation and thinning out denser areas.

Additionally, make sure that you separate the plants enough from each other and the walls to allow for sufficient airflow. You may be tempted to place them close together to save on space, especially if you are growing inside, where there is limited room. However, fitting an extra plant into the room will be meaningless if you end up causing mold growth from close placement and need to toss all of the plants anyway.

Prune Plants

Those with experience growing marijuana tend to prune their plants as they grow for various reasons. As mentioned, pruned plants will have more space for air to flow, helping to prevent mold. This is the most important point since moisture will accumulate in dense, overgrown plants, but the space by pruned plants allows for extra airflow, helping them to stay dry.

Boost Plant Immune Systems

You should also try to take steps to ensure that your plants are healthy with a strong immune system. This will make them better able to fight off mold. Opt for organic growing methods, such as compost tea, to provide extra nutrients when needed. Just make sure you do not use too much as this would lead to excess moisture and potential mold.

Keep Dirty Tasks Isolated

You should make a conscious effort to keep any “dirty” tasks separate from the plants. Things like scrubbing your trimming scissors, cleaning pots, or even filling pots are all included. These types of tasks may cause contamination, leading to mold growth. Avoid potential problems by creating a separate “dirty” room without shared air conditioning, ventilation, and heating with the clean areas.

Empty the Trash Regularly

To further maintain the cleanliness of the grow room and to prevent mold, make it a point to empty the trash from your grow space every day.

Keep Out Food and Drinks

The only food and drink items that should ever enter your grow space should be for your plants. This means just water and other nutrients for them. Food and drinks can easily encourage mold to form by providing moisture or a substance on which the mold can grow.

Use the Right Cleaning Supplies

Even something as simple as the cleaning supplies you use may affect the presence of mold in your space and its potential spread. Brooms definitely make it easy to clean up, but they also stir up mold spores and contaminants, encouraging them to spread. Instead, consider getting a HEPA filter backpack vacuum, which you empty outside of the grow space.

Can You Save Moldy Cannabis?

Knowing how to prevent mold on your cannabis is one thing, but what do you do if you see it? Can you save moldy cannabis? Is it still safe to smoke? Unfortunately, no. You cannot save moldy cannabis.

Depending on the extent of the mold, you may be able to just cut off the bud or a portion of the plant and leave the rest. Do not ever cook with or smoke moldy cannabis. This could be seriously damaging to your health, even resulting in long-term health conditions.

The Bottom Line

If you spot any mold growing on your cannabis, then you need to remove the affected part of the plant for health reasons. You do not want to consume mold in any way, via smoking or cooking with it. Get rid of moldy cannabis as soon as possible to prevent it from spreading.

Preventing mold is as simple as controlling moisture and humidity and ensuring there is enough airflow. Experienced growers know to closely monitor the growing environment and keep their eyes peeled for mold.

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