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The Signs of Damping Off in Cannabis Seedlings and How to Stop It For Good

When cultivating marijuana, issues sometimes arise. One such challenge is damping off in cannabis, which causes almost sudden death in your plants. Caused mostly by too much moisture and other less than ideal conditions, the disease can kill a seedling in hours

It's most common during the seedling stage, but it can also attack more mature plants. 

Silent and almost undetectable, there's no real cure once the problem strikes. A vigilant grower can spot the telltale signs of damping-off, and swift action may save a few of the plants. 

The reality is that the recommended remedies are more for prevention than cure. The best way to treat it is by stopping the disease from happening in the first place. Read on to find out all you need to know in combating this silent plant killer.

What does cannabis damping off mean?

Damping-off is a disease that often affects cannabis seedlings, cuttings, or sprouting seeds. Fungus is the primary cause of damping off in cannabis, but it's not the only one. Conditional factors can also play a role in causing the disease. 

Damping-off is caused by fungi such as Fusarium, Phytophthora, Pythium, and Rhizoctonia. The various fungi present different visual symptoms. Most appear as some form of spotting or discoloration. 

The fungi thrive in moist, cool conditions when the plant doesn't get a chance to dry. Ultimately, they infect the plants starting at the base of the bush, just below the soil's surface. The damping off fungus prevents nutrients and water intake, causing rot within the roots. This affliction spreads upwards and weakens the stems, ultimately killing the seedlings.  

damping off in young cannabis plants

What causes damping off? 

Fungi cause damping off in cannabis to occur. The damping off fungus can lie dormant until triggered by moisture or other climatic factors. Several different types of fungi can be responsible for the spread of this disease. Let’s take a look at the most common ones below:


Botrytis is also known as "bud rot" or "gray mold," and it's a frequent mold infection and can remain dormant for long periods. It comes alive with an increase in air humidity levels. Keep an eye out for caterpillars, too. Their droppings can cause the onset of Botrytis damping-off. 


This damping off fungus is a particularly problematic one. It lies in the soil and slowly clogs up the plant's xylem. This process starves the seedlings from nutrients and water. Without these, your crops soon start to die from what’s known as Fusarium wilt.


There are over 80 species of Phytophthora that could cause damping off of seedlings. They’re fond of very wet conditions, and plants growing in clay or compacted soil are most at risk. Some of the symptoms include rotting plant tissue, blight, and a general decline in the health of the foliage.


This nasty pathogen belongs to the oomycetes group and attacks both seedlings and older plants. The first signs appear as mild leaf curling and yellowing, or leaves dying around the edges. As the damping-off spreads, you notice lesions at the base of the plant, moving upwards towards the crown.


Rhizoctonia Solani can remain inactive in soil for several years. It's usually spread by the movement of plant debris and warm conditions. This damping off fungus is difficult to spot as it develops as brown rot on the roots. The lower portion of the main stem will turn a reddish-brown color as the infection progresses. The leaves and buds can also be affected by a change in color. 

All fungi need an ideal environment to fester and grow. Watering weed too often and too much is one reason for damping off in cannabis seedlings and older plants to creep in. The fungus often lies dormant in a non-sterile growing medium triggered by humid conditions. Any of the fungi listed above flourish with the right temperature and humidity. 

Inadequate airflow is another culprit for damping-off attacks. Ensure that your substrate isn’t clogged and allows for proper drainage and air circulation. 

You also have to be extra careful when using mulch from old foliage. If any of your plants had an infection, it could easily spread to any new crops you use the mulch on. Purchase sterile mulch and feeds from your local nursery if you're unsure.

Can damping off be reversed?

Depending on which fungus attacks your plant, there are instances where you can reverse damping-off. If you notice the signs of an infection, even if you're not sure which fungus is to blame, take immediate action. 

Make a homemade fungicide for plants to use when you see any strange spots or limp foliage. A quick one to try is a mixture of canola oil, garlic, lemon juice, and hot peppers. The ingredients have antifungal properties that help to combat any infections. Use it by spraying the foliage from the bottom to the top of the plant. 

If the damping off in weed seedlings is in the early stages or one of the less deadly fungi is the cause of the infection, you can lessen the damage with light. These fungus hates bright lights, so use high-output fluorescent bulbs over your seedlings

If you notice any infection, remove the afflicted plants from the rest of the crops immediately. You may avoid the disease affecting the remaining plants if you remove them soon enough. Then, treat and try to save the ailing bushes in a separate area without putting the rest of your crops at risk.

damping off in a cannabis seedling

Common signs of damping off you need to watch out

It's often difficult to spot the signs of damping-off before it gets serious enough to kill your plants. When most growers realize their crops are infected, the disease is already too far along to stop. It attacks just under the soil line, so you won't notice when it starts. 

It takes hold so fast that a healthy seedling can drop dead within a day without you even knowing it was infected. When that happens, it's too late to do anything for your plants. Being overly vigilant is the only way to stop the spread of fungicide damping off. 

The first visible sign of damping off cannabis is the rotting of the stem in seedlings. Usually, it starts at the base of the plant and extends upwards. The next stage is a discoloration of the foliage going from green to reddish-brown.

Another sign is the appearance of white spots on the bottom part of the stem. Simultaneously the limb will look thin and darker in color. It may seem as though the stem is dehydrated with a loss in contour. If you manage to spot this and the plant is still standing, it's likely only a few hours before it falls over. 

Some fungi, such as the Botrytis, appear as brown water-soaked circles. Bit by bit, the plant loses its green color and becomes gray

Once the disease has completely taken over the seedling, you'll find it lying down, bent in the spot where the stem is the weakest. Unfortunately, there’s nothing you can do for the plants once they've fallen, and it's best to discard them. 

How to fix damping off (if it is possible)

The harsh truth is that once damping-off take hold of your plants, there's almost nothing you can do about it. The fungus moves so fast that the crops can die within hours of you noticing symptoms. 

Remove the infected seedling

You need to remove the infected seedling as soon as possible to stop the spread of damping-off. Usually, though, if one plant is infected, chances are your entire plantation has the same problem. 

If the plants are already lying on their sides, it's too late to save them. Inspect the rest of your crops for the telltale signs of damping-off and treat the still standing bushes instead.

Apply hydrogen peroxide

An emergency action to stop the spread is applying a hydrogen peroxide solution to your plants. Make a 3% strength mix of hydrogen peroxide and water, and sprinkle 20 drops on the soil of each seedling. The chemical will kill the fungus. 

However, there's no guarantee that your precious cannabis crops will make it, especially if the disease is too far along. The best is to isolate the infected plants while you treat them. If they perish, get rid of them somewhere far from your other bushes to prevent the spread of the damping off fungus. 

How to prevent damping off in weed

Even though it may seem there's no way of stopping this frustrating disease, there are several ways to prevent damping off. Put these measures into place from the very beginning when you first plant your seeds. Since the disease is so destructive, prevention is the best cure for this and many other plant afflictions. 

how to prevent damping off

Control the moisture and humidity levels

An excess of moisture is one of the main reasons fungus develops. This situation often arises from overwatering or not trimming thick foliage. You should avoid watering your plants too much and make sure the pots have enough holes to allow for drainage

Check that you don't pack the soil too compact so water can pass through. Damping-off likes to breed in waterlogged soil. If your marijuana crops are thick and bushy, trimming excess foliage allows the plant to dry between watering sessions. 

Another way of decreasing excess humidity indoors is to have a vent at the top of the grow tent to allow proper ventilation. Install a ventilation system to circulate the air and cool the area if you're using a room to grow your marijuana. 

Sterile Medium

When germinating your cannabis seeds and throughout the seedling stage, use only sterile growing mediums. Suitable options include Rockwool, jiffy pellets, or perlite

Don’t plant your seeds into dirt, and don't reuse old potting mixes. Using soil that you're not sure the source of is a sure way of introducing some form of fungus into your crops, increasing the chances of damping-off. 

pH and growth enhancers

It's best to avoid feeding your seedlings with nutrients and teas in the first two weeks of growth. Giving nutrients to your young saplings at this stage promotes the growth of pathogens, with a possibility of damping off. It also hampers your seedlings from developing a healthy root system. 

Once your plants sprout their first real leaves, begin with a light dose of nutrients. Make sure that you're checking your pH levels in the water using a meter. The ideal pH reading should be 5.0-7.0

Always use clean utensils

Ensure all your tools are clean when germinating seeds or replanting your seedlings. Take extra care to wash all your pots if you plan to reuse them. If damping off fungus is present in the pot or utensils, it could transfer to your new plants. Clean everything you plan to use with water and bleach to kill pathogens. 

Natural protection 

There are some methods to use that could help combat fungal infections, including damping off in seedlings. You can use homemade fungicides to ward off pathogens using natural ingredients. You can also try Pythium Oligandrum grains on the soil—spreading them on the soil's surface can deter certain fungi as the parasite feasts on them. 

Mind the temperature

Damping off fungus thrives in warm, moist conditions. Many growers believe that seedlings need to be kept in a hot, humid environment to grow bigger. The best temperature for growing weed is between 68 and 77 degrees Fahrenheit. Try to keep to that range since anything hotter triggers most pathogens. 

Prevention is better than cure

Any experienced cannabis cultivator will tell you that disease prevention is better than a cure for healthy crops. It's especially true for damping off cannabis attacks. The plants rarely come out alive once the dreaded fungus takes hold. 

To prevent damping off in marijuana seedlings, ensure that your crops have plenty of light, adequate air circulation, and not too much moisture. Overwatering and high humidity levels are the biggest cause of pathogen attacks. 

If you happen to find yourself plagued by signs of damping off, isolate the infected plants and treat them with hydrogen peroxide. Keeping marijuana crops healthy for an abundant harvest is sometimes difficult. Besides damping off from fungus, there are plenty of other plant illnesses.

Pop on over to our Homegrown Cannabis Co. troubleshooting page to find out how to deal with other threats to your marijuana garden. If you found this article helpful, share it with friends to help them on their way to reaping huge yields.

About the author: Derek LaRose

Also known as Kronic from The Cannabis Kronicles, Derek LaRose is a young ambitious cultivator and a staple educator for indoor cultivation.

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