Begonia stem rot is a common disease of begonia plants. These shade-loving perennials emerge from a dormant tuber every spring, only to produce fresh flowers from midsummer to fall, but with this is a hazardous plant disease, that will most likely kill your Begoniaceae family plant.

Begonia Stem Rot Preventiion

In this article, we’re going to see what stem rot is, what triggers this disease as well as how to treat it.

What Reasons Can Cause Begonia Stem Rot?

The reasons that cause begonia stem rot are being infected with Pythium Ultimum bacteria, being overwatered, and lastly root rot. These reasons will cause the stems of the plant to look weaker, and it will slowly spread to the rest of the plant as well. 

Usually, your begonia will react with a blackened stem. However, this may be the last symptom that shows your begonia is already too far gone. This is why, both overwatering and mildew disease will ascend from the roots and up; as the stems weaken, it becomes an issue. 

– Pythium Ultimum Bacteria

Begonia stem rot is typically fatal to the begonia plant, at least for the remainder of the growing season. It is caused by the Pythium Ultimum bacteria which is triggered by the wet soil conditions, and it spreads slowly, but steadily from the roots above. You can immediately guess that the overwatering will be your most likely issue here, or that the medium is too humid for the plant, that the bacteria have increased in their number and it looks wilted. 

Stem rot is a common issue with begonia plants, and will most commonly attack planter plants such as the Begonia Maculata variety. In most instances, this disease will show similar signs to powdery mildew at first, but if you do a closer inspection, you can see that the stem is rotting away.

– Overwatering

Developing and germinating from the bacteria, this fungal disease will begin its life in water-clogged conditions in your soil. From there it will spread easily to your stem and even the closeby plants if you grow begonias in group plantings or mixed flower beds.

Reasons Can Cause Begonia Stem Rot

Just as you start to overwater, different fungi will be the sole cause of the begonia stem rot. But it’s not the pathogen we should be worried about as this one can be naturally present in your soil without ever being triggered.

This is because it is the triggering part that we should be worried about, which is that the stems can no longer stay healthy through excessive irrigation. 

– Root Rot

Your stem rot disease will trigger once the roots become over soaked, so as soon as you spot the slowing down of growth or even dropping leaves, you should cut back on watering and see if the begonia springs back to life. If that doesn’t happen in a few days, you will likely deal with stem or root rot

Also, if your soil remains wet for longer than other plants’ soil, this means that your roots have begun to die away and aren’t drinking water properly. Severe and too far-gone cases include black stems that just crumble and fall upon touch. Since the stem is the part that carries the water up to the leaves of the plant, the damaged roots will also hurt the stem. 

The root’s rotting disease is triggered when this pathogen is found in a humid and watery environment for a prolonged period. This environment causes spores to germinate and spread like wildfire. Once this occurs, the infections are pretty difficult to control and even prevent them from reappearing every year in the soil in which it was activated. 

Spotting the infected plant is only the beginning of your problems, as you’ll have a short time to deal with it before it’s completely dead. And you’ll have the remaining pathogens to deal with to prevent the spread.

How To Treat and Prevent Stem Rot of Begonia?

To treat and prevent stem rot of begonia you must stop overwatering it, and use a well-draining soil mix. You should spray fungicides to tackle the bacteria, and lastly, if the case seems impossible, throw the plant away if it is fully wilted. 

– Don’t Overwater Your Plant

Moisture is the number one medium of stem rot activation, so the best thing you can do is adjust your watering regime to be optimal for the plant. If you spot the wilt of the stem very early in the stage of growing, make sure that you stop watering it for a couple of days and resume when the soil feels dry to the touch. 

Remember a few days of drought won’t kill your plants, so you can water only when sure that the topsoil has gone dry. One trick you can do to prevent the water from staying in your containers for too long is to drill some drainage holes at the bottom. That way you can ensure that the water runs through your soil and isn’t staying and going stale.

– Use Well-Draining Soil Mix

Water is essential sure, but healthy roots need air too! You need to ensure that the roots get their breathing time, both by watering and by the soil mix you use. Begonias love a standard organic potting compound, but feel free to add some inorganic material like perlite or lava stone. 

However, you should also think about the fact that if you’re afraid you’ve gone too far with the water, you can always wrap the soil in plastic and let it be for a few days. This will kill off any pathogens inside and prevent the roots from dying, because you won’t be feeding them with their growing medium. 

No matter how your soil was adequate for the last plant, the pathogens will travel with it and pose a danger to the next plant in a row. So better use a fresh soil mix and prevent any risk of contamination to give your plants the best head start.

Treating Stem Rot of Begonia

In addition to this, you want to disinfect the entire operating area and the place where your plant has been sitting — use a mixture of water and rubbing alcohol for this.

– Use Fungicides

Fungicides can be used to prevent stem rot in the first place. But remember, they are prevention tools and shouldn’t be used if the infestation has already happened. 

You can either buy them in your local garden center or use a homemade recipe. A popular natural fungicide is a neem or horticultural oil — mix them with some water and apply the mix early on in the spring. 

Just as you spread these oils on the plant, you will see that in such a short time, the fungi that have been tackling the stems would slowly start to die. When this happens, you must continue with giving it the right care, so that the stems would come back to life again. However, be very careful of how much water you would give it when it is in recovery.

– Throw the Plant if it Fully Wilted

It is hard to see your plant die, and if it has, then you cannot wish to bring your hopes up if you’re dealing with that state; likely, it won’t make a comeback. But the treatment involves all the necessary steps you should take to prevent the disease from spreading to other plants nearby. 

In this case, you must get rid of the plant because the bacteria it has would spread to the others surrounding it, and you don’t want that. Pull it entirely out of the soil, roots, and all, and wrap it in an air-tight container and directly to the trash bin, no stopping.

You can also try to burn it if the situation allows you, but whatever you do, you need to get rid of it. Never use sick plant material inside your compost bins or try to give them any other purpose. After this, you should get rid of the pathogen-infested soil too.

Do this like you did with the plant or simply gather everything inside a single bag. If you’re short on plastic containers, you can try to clean them up for reuse, but it’s best to get rid of these as well. 

Stem Rot Is a Heavy Disease


Begonias are beautiful flowering plants that adorn any place they find themselves, the occurrence of stem rot can seriously damage and destroy this beauty.

So, let’s remind ourselves of what we’ve said: 

  • Always remember to inspect your begonia as soon as you see some signs! The early offset can look like mildew, stunted growth, and drooping leaves.
  • Stem rot is a heavy disease that will likely kill your begonia plant, so you better get rid of all evidence of disease as soon as you spot it. Unfortunately, your plant too!
  • To prevent stem rot, always practice good watering, ensure you have a porous potting mix and never use old potting soil!

Now that you know how to prevent this deadly disease, we’re sure your begonia will have one healthy and happy life! So happy garndening. 

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