Why Are My Indoor Plants Growing Mold?


Recently I was surprised to see a white and yellow mold or fungus on one of my houseplants. I realized that if I wasn’t already familiar with seeing this, it could be rather disturbing. That being said, I thought it was time to explain why you see mold on your houseplants, what you can do to prevent it and how to properly remove mold from your indoor plant.

Why are my indoor plants growing mold? Mold commonly develops on indoor plants due to adequate sunlight, over-watering, poor ventilation, or your plant’s pot or container has inadequate drainage.  Mold is often treatable in houseplants by removing the offending soil or cutting the affected plant parts off. 

If you have mold growing on your indoor plants, you’re not going to want to miss this article. Ahead, I’ll discuss how to identify houseplant mold. I’ll also talk more about the conditions that let mold thrive as well as share some handy tactics for mold removal. Keep reading!

What Is Mold and What Does It Look Like on Houseplants?

You’ve probably seen mold a time or two in your life before, but do you know what it truly is?

Mold is a fungus. It comes in all sorts of colors, including purple, green, orange, white, or black depending on the source of mold you’re dealing with.

Mold can form on almost any surface, from bathroom walls to upholstery and yes, your plant’s leaves or soil. All it takes for mold to grow is an environment that’s rich in moisture.

That’s why mold develops more in your bathroom than in your living room or bedroom. The dampness and humidity of your bathroom as you shower can linger in the room if you have inadequate ventilation. That makes an ideal environment for mold.

Since you water your houseplants often, you’re also giving mold a home around your plants. 

You might not have known, but mold is incredibly common. No, not overgrowths of mold necessarily, but very small particles in the air.

Each time you step outside, you’re breathing in microscopic mold spores that are floating around in the air. These aren’t dangerous to your health in small quantities unless you have a mold sensitivity or allergy.

In larger quantities though, mold can cause health maladies. You may have breathing difficulties if mold gets bad enough. For those with mold allergies, these breathing troubles can be even more pronounced.

Mold overexposure can also lead to skin irritation, itchy and red eyes, wheezing, and nose stuffiness.

Those symptoms manifest upon exposure to allergenic mold, but mold can also be pathogenic or toxigenic. Pathogenic mold is dangerous for those with poor immune health, as they’re most prone to symptoms from this mold.

Toxigenic mold is even more dangerous, as it’s toxic. For anyone who’s exposed to toxigenic mold, there’s a risk of severe health effects and even death. 

The Types of Houseplant Mold

You don’t want to breathe in a lot of mold if you can help it, then. The first step to removing mold is identifying it. Most houseplant mold is typically white, but not all. This white mold will have a fuzzy texture if the growth is significant. 

Mold can also be gray, which is due to the necrotrophic fungus known as botrytis cinerea. This mold will linger in the foliage of your indoor plants as well as its soil. The gray mold spores get into the plant’s tissue and make it collapse, so gray mold is very deadly to your houseplants.

Sooty mold may be dark green or black in color. It affects the surface of the soil as well as the plant’s base. Scales, insects I’ve written about on this blog, also typically come with sooty mold, as the mold is indicative of a scale infestation. 

You might also notice a powdery substance on your indoor plants. This isn’t mold, but rather, mildew. Mildew is a fungus that’s always white. Unlike mold, which can look fuzzy, mildew has a powdery texture. It will also grow on different parts of your houseplant, such as the stems. Mildew can travel to the soil as well. 

Why Do Indoor Plants Grow Mold?

Mold can affect any houseplant, as can mildew. If you have a mold problem in your indoor garden, then it’s more than likely caused by mistakes in care, negligence or a surrounding environment that has declined in care since your plants were placed there.

Here are the four chief issues that will likely lead to mold and/or mildew growth among your houseplants and their soil. 

Lack of Sunlight

Without the proper amount of light, your houseplants can’t photosynthesize correctly, which inhibits their growth. Once mold develops due to lack of proper light it compounds the issue and diminishes the plants growth even further.

If you read this blog regularly, then you know that sunlight is the best source of light for your plants. How much sun a plant needs and from which angle (such a southernly or easterly-facing window) varies depending on the houseplant species in question.

Sunlight is not always bountiful, especially in the winter, which is when you’ll use artificial grow lights. Have one or both these light sources available to combat mold. 

Poor Ventilation 

What is the ventilation like in your home or office? Hopefully, it’s good, or you could be in trouble. A proper ventilation system lets clean air enter and travel throughout a space to restrict the spread of allergens and viruses. 

If you’re wondering what the ventilation is like near you, look for several signs of poor ventilation. These include a buildup of heat that takes a while to dissipate.

Odors might linger for longer than seems appropriate. Metal pipes will look rusty, grout and wall tiles can become discolored, and shower doors and glass windows have a frosty appearance that doesn’t fade for a while. 

If your home or office has the above signs of poor ventilation, then mold will surely follow. Not only will this affect your houseplants, but likely also fabrics, wooden surfaces, walls, and floors. 

The reason ventilation leads to mold is that when moisture develops in a room, the lack of ventilation does not disperse that moisture. Instead, it sits and sits, collecting and creating a hotbed for not only mold, but mildew too. 

Overwatering

Almost all indoor gardeners have been guilty of feeding their houseplants too much water at some point, but you live and you learn. Overwatering is dangerous for your houseplant in a variety of ways.

First, it can lead to root rot, a plant disease that occurs when water oversaturates the roots, killing them slowly yet surely. Second, overwatering also creates a perfect home for mold, as now the bacteria has a deep, dark, wet place. 

Lack of Drainage

Inadequate drainage is just as damaging to your houseplant, as it invites mold. When water gets trapped in pockets of soil within your plant, again, root rot can take hold.

Poor draining soil will also become soggy (and moldy) before too long.

Always check your houseplant pots or containers before you get your plant settled in. The pot or container should have drainage holes that are big enough for water to flow out.

If the only pots or containers you currently own don’t have a hole in the bottom for drainage then you’ll definitely want to read: 13 Indoor Plants That Don’t Need Drainage.

A saucer underneath the pot is important for fighting mold and mildew caused by excess water that would otherwise leak onto your windowsill or living room floor adding to the exact ecosystem you’re trying to avoid creating.

Avoid adding rocks to the bottom of your plant’s pot or container. The rocks can plug up the drainage holes, impeding drainage where you’d otherwise not have a problem. 

Your potting soil can also prevent necessary drainage, so shop carefully. Choose potting mix with perlite, sand, bark or other composted plant materials, and peat moss. These ingredients all encourage water drainage. Some ingredients like peat moss don’t last forever, so you’ll have to replace your plant’s soil every six months or so. 

How to Remove Mold from Houseplants and Their Soil

Mold should not be allowed to stay on your houseplants, even if you only see trace amounts. For one, the mold is likely to spread. As it worsens, the chances of the plant dying increase.

Also, any mold is indicative of a less than optimal houseplant environment, so you want to first get rid of the mold and then modify your environment the plant or plants are in and then adjust your care regiment.

Depending on whether you see mold on only your plant’s soil or the plant itself, your removal methods will differ.

Here’s what you need to do. 


Clearing Mold from Your Houseplants

First, I’d advise you not to mess around with houseplant mold indoors. Move your plant to your backyard and work on it there. Choose an area that doesn’t have outdoor plants or nearby trees, as the mold can spread if it’s active. 

With a wet paper towel, gently clean your plant’s leaves, both sides. Don’t keep using the same dirty, moldy paper towel to wipe down each leaf on the plant, so you want to have a handful of paper towels at the ready. 

You can now see the leaves more clearly without any dormant mold on them. Some active mold may still remain, and this typically doesn’t come off with a paper towel. Instead, you’ll need disinfected gardening shears. The whole leaf will probably have to go if it’s riddled with active mold, so slice it off.

Buy some fungicide if you don’t already have it. Fungicide shouldn’t hurt your plants, but it will kill any hints of mold you might not be able to see.  When you’re done spraying the fungicide, bring your houseplant inside.

Clearing Mold from the Soil

If the mold is only on the houseplant’s soil at current, then your removal job is easier. You can leave your plant where it is indoors. Take a clean spoon (preferably one you don’t intend on eating with again) and scoop out any areas of mold. Sift through the soil several inches deep to check if the mold has spread.

If you can still work with the original soil because the mold was confined to the top layer, then apply a natural antifungal after you’re done scooping. In severe cases of mold where there’s too much to scoop out, you have to start over, repotting your plant with fresh, well-draining soil.

Related Questions

How do you know mold is making you sick?

During cold and flu season as well as allergy season, it can be hard to confirm your source of illness. You might assume it’s just the time of year for sickness until your symptoms persist longer than they usually do.

To tell whether it’s mold that’s leaving you constantly under the weather, review your symptoms. If you’re experiencing fatigue, watery eyes, sneezing, coughing, a runny nose, sore throat, and a headache, it could be due to mold.

Does cinnamon kill mold in soil?

If you’d rather go the chemical-free route when treating your houseplants for mold, you have a few antifungal options that are safe for plants. Apple cider vinegar is one, as is baking soda. Cinnamon powder also works as a powerful and natural antifungal.

Do keep your eyes peeled for insects though. Flies love apple cider vinegar, and plenty of other bugs are attracted to sugary stuff like cinnamon. 

Fred Zimmer

I'm a lover of plants, animals, photography, & people, not necessarily in that order. Currently, I'm focused on photographing indoor plants & chachkies. I write & rewrite articles about creating an environment where indoor plants can thrive. I'm good at listening to music but bad at shopping to muzak.

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