Why Do Indoor Plants Get Fungus?

One of the most common problems indoor plants have is fungal growths. It may be caused by a variety of factors, and if not treated in time, it may kill your beloved plant. Of course, this is something we want to avoid. In this article, you will learn about the causes of fungus in your plants, the common fungi that infect plants, how to identify and treat the fungus in plants, as well as the other diseases that might affect your plant.

Fungus in indoor plants occurs when it is poorly maintained. This means your plant is not getting enough air and light. It also is common in plants that have been overwatered. Too much water will cause rotting and promote the growth of fungi. It is quite common for indoor plants to have this problem.

For tips on watering your plants see “How to Care for Houseplants”.

What Causes Fungus in Your Plants?

A fungus can be quite stressful to have on your plants. These microorganisms attack leaves, eventually causing them to brown and fall off. They can also penetrate through the roots and block their water-conducting cells which leads to wilting. One thing is for sure, different fungi, thrive in different kinds of environments. It is quite difficult to pinpoint a specific condition that would promote fungal growth. However, these are some factors that may cause fungal growth:


Most fungi thrive in a wet environment. These types of fungi are the ones that are commonly seen in indoor house plants. There are some fungi that thrive in dry conditions, such as those that are found in dried grains.


Most fungi thrive at 70 to 90 degrees Fahrenheit, but there are some species that grow below 32 degrees, and even at 150 degrees.


In theory, most fungi grow in the dark since moisture is often associated with placed that are humid and devoid of light. Then there are others that are fine with direct sunlight, which has been an issue for outdoor gardeners.

Depending on the kind of fungi, these are the possible factors that may promote its growth. If you are noticing signs of fungal growth on your plant, it would be best for you to identify the kind of fungus it is before treating it.

What is Fungus?

A fungus is a eukaryotic heterotroph. They are organisms that acquire energy and nutrition by consuming other organic substances. Most fungi are visible to the naked eye, and there are a few that are microscopic. Fungi, in general, have a wide range of roles. They can be pathogenic or beneficial to plants, animals, and humans.

In plants, some fungi attack leaves and consume the nutrients which kills them in a short period of time. Since fungi reproduce sporadically, the chances of this disease spreading among other plants in your garden would be high. Once spotted, you must treat it immediately. Other fungi live in the soil, and because of moisture, they grow at a rapid rate and enter the roots of your plant. These fungi then block the cells responsible for collecting and absorbing water. Without these cells functioning, the plan will wilt and die.

We also have fungi like mushrooms that don’t really harm other plants. Contrary to popular belief, mushrooms do not consume the nutrients meant for your plant. In fact, they improve the quality of your soil which is great for your plant’s growth. But be warned, not all mushrooms are safe for humans and animals. They are divided into edible and poisonous varieties. So if you have pets, it would be safer to remove mushrooms that may possibly grow in your potting soil.

Just like any other organism on the planet, fungi have an important in our ecosystem. They are often put into the negative light, but without them, there wouldn’t be cheeses, probiotics, bread, and other items we know and use every day. They are influential in the nutrient cycle of the human population on such a large scale.

Common Fungi Infecting Plants: How to Prevent and Treat Them

There are around 120,000 species of fungi in the world today, and only 8,000 of these fungi affect plants pathogenically. Here are a few fungi that are commonly seen in indoor houseplants:


There are two kinds of mildew, downy and powdery. Downy mildew prefers cool and damp conditions while powdery mildew thrives in dry soil and humid environments. They affect leaves and other parts of the plants that grow above ground. They are white in color and will turn the plant yellow until it completely browns and dies.


Keep you plant well-hydrated but avoid letting it sit in water. Since this fungus thrives in moist or damp conditions, completely dry out your soil in between watering.


In the event you already have mildew on your plants, here are some remedies you can easily access from your local gardening center:

  • Triadimefon
  • Triforine – Not safe for plants intended for human consumption.
  • Thiophanate-methyl
  • Propiconazole
  • Sulfur
  • Potassium Bicarbonate – Baking Soda

One common remedy used by seasoned gardeners is a baking soda mix.

You just need 3 tablespoons of baking soda, 1 gallon of water, 1 tablespoon of cooking oil, and 2 to 3 drops of dishwashing soap. Mix all the ingredients together, transfer into a spray bottle and use at least once a day until needed.

Leaf Spot

Fungal leaf spots are common in both outdoor and indoor plants. You will notice discolored spotting on the leaves. It is often seen in humid and damp conditions when fungal spores are able to easily attach. Once it has settled in, sporulation begins, and the spots grow. If not treated, the whole leaf will turn brown and fall onto the soil, and the new fungal spores will be ready to infect the next leaf that it can attach to.


It is quite easy to identify plant rust. It is characterized by a yellow-brown color on the stem and leaves. It is often on the underside of the leaf, and it starts out as specks of dust that eventually grow into bumps.


The fungi that cause leaf rust thrives in damp conditions with poor air circulation. It is important that you do not overwater your plant. Check the soil before watering and make sure it is not moist. When your plant sits in a pool of water, you can be sure that there will be something wrong.


Prune affected parts of your plant and dispose of them properly. Do not place them in the compost pile. Remember, fungi produce spores which will just fly through the air once mature. Treat your plant with commercial fungicide you can find at your local garden center, or you can opt to use neem oil.

Root Rot

There are two causes of root rot: overwatering and fungus. When plants are overwatered, the roots start to decay due to the lack of oxygen. They then will spread to healthier roots and kill them even if you have already corrected your soil’s conditions. In the fungal aspect, there are about four species of fungus that cause this, and this is due to high moisture content in the soil. The fungal spores found a way to the moist soil and ended up consuming the roots and its nutrients.


Simply stop over watering your plant. Depending on the type of plant you have, you should check the soil before watering. If it still feels moist, let it be. It helps to have potting soil that promotes good drainage.

Time is of the essence when you have a plant with root rot. Remove your plant from the soil it is currently in, and wash the roots gently. Trim roots that are obviously affected by the rot. Dip the remaining roots in a fungicide solution to kill any remaining fungus and repot your plant in a new pot and soil. If you wish to use the same pot, clean it thoroughly with bleach before repotting your plant.

Black Leg

It is basically the blackening of the lower stem of your plant. This disease is caused by a fungus called Phoma lingam that thrives in cold and wet conditions. It often occurs after winter, especially when you have been over watering your plant.


Reduce watering during cold or winter seasons. Plants are usually dormant around these times, meaning they don’t really absorb much of the water. By cutting back on watering, you are able to avoid the growth of fungus that would lead to blackleg.

Once any of your plants show signs or symptoms of blackleg, be sure to isolate and destroy them before it can contaminate others.


Unfortunately, there is no effective treatment for blackleg.

Botrytis Blight

Quite common in humid conditions, this disease is caused by the fungus Botrytis cinerea. They often attack tender parts of your plant; like flowers, fruits, and leaves. It would present as discoloration, wilting, brown lesions, and gray spores.


Ideally, healthy plants are not prone to this fungus, as it only attacks weak ones. Be reminded to keep the foliage dry and promote good air circulation by pruning your plants every now and then.

Sanitation is key to preventing the spread of this disease. If you have noticed one of your plants already suffering from Botrytis Blight, the first thing you should do is remove affected parts and incinerate them, then proceed with treatment.


Prune affected parts of your plant and apply fungicide on the rest of your plant. Some experts also recommend the use of 5% Hydrogen Peroxide to kill the remaining Botrytis spores. Be sure to use these chemicals in moderation. Too much will damage your plant.

Do not forget to disinfect any tools you have used when handling this fungus. Simply clean them with at 10% bleach to prevent further spreading.

Sooty Mold

Sooty mold grows from the secretion of plant pests like scales or aphids called honeydew. These pests cover the leaves in honeydew, then spores of sooty mold land on them and start reproducing.


If you have scales or aphids on your plant, you need to address that first. By the time they have been removed and are no longer producing honeydew, the sooty mold will stop producing altogether.


Neem oil is an effective pesticide for scales and aphids, and is also an efficient fungicide for sooty mold.

Reminders When Dealing with Infected Plants

One thing you would definitely want to avoid is spreading the fungal spores around your garden. Here are some tips you can follow to make sure your other plants are safe from any fungal disease.

Isolate Affected Plants

For plants that have been infected with fungus, the first thing you must do is separate them from the other plants. Fungi spread fast since the spores are airborne. With the right conditions, they will be able to reproduce fast and eventually destroy your whole plant population.

Wash Hands

It is important to wash your hands thoroughly in between working with plants. Especially when you are caring for a plant that has been infected. This will prevent spreading throughout your garden.

Sterilize Tools

Like your hands, tools may also serve as a transport medium for fungus. When you have used tools on a plant that is positive for a fungal infection, you must disinfect them with a bleach solution. Simply mix 1 part of bleach with 9 parts of water to achieve a 10% bleach solution which is effective in killing live spores.

Water Moderately

Always keep in mind that your indoor plants do not need to be watered every single day. Depending on the type of plant you have and the conditions they are in, watering them at least once a week should be enough.

Avoid Overcrowding

In the event of a fungal infection, one problem would be spreading. If you have way too many plants in one space, you can be certain that the fungal spores would’ve already affected other plants. By giving each of your plants a good amount of space in between them, you will have good air circulation and fewer chances of cross-contamination.

Other Diseases

Aside from fungal diseases, plants are also susceptible to diseases that come from other microorganisms. Here are some common diseases associated with indoor plants:

Bacterial Disease

It is quite hard to detect bacterial diseases in plants since they present similarly to fungal disease. Oftentimes, gardeners treat for fungus rather than bacteria because of misidentification. They are also difficult to control, which is why it is best to prevent bacteria from infecting your plant by following these practices:

Plant bacteria resistant varieties and hybrids.

  • Prioritize sanitation with tools and materials used for gardening.
  • Provide ample air circulation, and exposure to sunlight.
  • Apply pest control to eliminate possible vectors of bacteria.
  • Opt to use biological controls to manage bacterial infection
  • If you need to use antibiotics, use them appropriately and when needed to avoid bacterial resistance.

Not all kinds of bacteria are pathogenic to plant. In fact, there are species of bacteria that is needed to convert carbon in the soil and make them useful as nutrients for the plant. Pathogenic bacteria often occurs when a plant is not optimally given the care it needs.

Signs and Symptoms of Bacterial Infection

  1. Bacterial Oozing
  2. Lesions
  3. Leaf Spots with Yellowish Halo
  4. Canker
  5. Crown Gall

Pest Infestation

One of the most common diseases you can find in indoor plants is parasites. There are lots of bugs that can infest your plant, and most of the time, they go unnoticed. If you have noticed an evident change in your plant in terms of color or growth, start looking for signs of infestation. Most plant bugs are quite visible. Here are a few common pests that can be found in your houseplant:

  • Aphids
  • Spider mites
  • Mealybugs
  • Whitefly
  • Scale Insects
  • Thrips

Pests will always find a way to your plant. You must be observant and proactive to keep them from infecting your entire garden. Here are a few tips on how to avoid the spread of the infestation:

  1. Isolate infected plants for at least a month during treatment.
  2. Clean your plant pots regularly and remove dead leaves.
  3. Clean your plants every now and then with a soft cloth and lukewarm water.
  4. Inspect your plants regularly to know if they have bugs or not.

As much as possible, pests should be controlled since they can possibly cause bacterial, fungal, and viral diseases. By ignoring their existence, you may create more problems for your garden.

Viral Disease

Quite similar with fungal and bacterial disease, viral infections may overlap with them at one point or the other. The only problem with viral infections is that there is absolutely no treatment for them. If your plants are positive for a viral infection, they should be destroyed immediately by burning.

Signs and Symptoms of Viral Infection

Mosaic Leaf

Crinkled Leaves

Knowing how the fungus is attracted to our plants and how to stop them from sporulating is definitely important. At the end of the day, our goal is to keep our indoor garden healthy with plants that are fungus-free. By taking precautions and practicing a good routine with your plants, you will be able to avoid any disease that may affect them. Always remember, an ounce of prevention is worth a pound of cure.

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