Mold on Plant Soil- What Causes It and How to Eliminate It?

Choosing your houseplant soil can be a daunting task sometimes, and even when you find the right one for your indoor plants, some problems can still occur. One of the main types of contaminated soil is moldy potting soil.

There are different kinds of mold on plant soil, they vary in the way they look, and in the reasons why they appear. Similarly, there are different ways to prevent mold growth or to get rid of mold in case you already have contaminated potting soil.

Why Mold Growth Appears in Houseplant Soil?

What’s common for every kind of mold growth is that it thrives in places with too much moisture. Here are the situation which lead to its development:

Overwatering

Places with excess water are the ones that are guaranteed to have mold growth in them. So, the best thing you can do is to make sure you’re not the one who’s causing the problem. Overwatering can also cause root rot, and having that problem together with mold growth can cause many problems for your plant.

Leaves decomposing on the surface

Decaying organic matter is another thing that can easily get fungal spores of all kinds. Having a buildup of dead leaves on the potting soil surface can bring the mold to it.

Contaminated soil

Sometimes, the houseplant soil itself can be the problem. Not all soil is sterile potting soil, and mold spores can exist within the potting soil even before you bring it home.

But, if your bag of plant soil sits in a dark and moist place, you can have houseplant soil mold form, and then cause problems with your plants once you use it.

Related: Can You Reuse Potting Soil?

Poor drainage 

If your pots aren’t appropriate, water can store for a long time in the houseplant soil. Damp houseplant soil can then cause things like root rot and, obviously, soil mold. To avoid poor drainage, you should look into getting pots that have drainage holes.

Poor air circulation

It’s common to have poor air circulation among your indoor plants. Most indoor plants suffer in the winter when windows tend to stay shut.

Another thing that can be the cause of poor air circulation, is the placement of your plants. If they are somewhere in dark corners or shelves that are cramped, it’s more than likely that your plants don’t have the air circulation they need to be healthy.

Types of Mold on Plant Soil

There are different kinds of mold that can commonly grow in houseplant soil. Mostly, they are differentiated by their looks and the most important characteristic for identifying what kind of mold you’re dealing with is the color.

The most commonly found are white mold, yellow mold, and green mold. Below you will find something more about each kind, and also the solutions for the mold growing in your plant soil.

White mold or dusty-looking mold on soil

If your moldy soil is white or dusty-looking then the situation is not as harmful as you might have thought. The white mold that grows on the surface of the potting soil is a type of harmless saprophytic fungus.

However, even though the saprophytic mold is harmless itself, it can be an indicator that there is something wrong. Usually, this kind of white mold appears when your plant is dealing with overwatering, poor drainage, or contaminated soil.

How to get rid of white mold

If you are dealing with saprophytic fungi, the resolution for this problem is usually very simple. To get rid of mold, you should just scrape it from the surface of the potting soil. But, since it can be an indicator of some problems, it’s in your best interest to do a bit more.

After you’ve cleaned up the moldy soil, you should repot your plant, and make sure you’re using fresh and sterile soil as some mold spores can still stay in the old houseplant soil even after you’ve got rid of the top layer.

Mold spores can also stay on the walls of the old pot, so you should make sure you kill mold from the pot as well. To do this, just soak the pot in a solution made from 1 part of bleach and 9 parts of water, for around 10 minutes. After soaking it, take the pot and scrub it using water and dish detergent.

When you have your plant all fresh and repotted, make sure to keep the plants healthy to prevent mold growing again.

To prevent mold, water your plants properly, which means watering them just enough and not overdoing it. Soggy soil is usually the main root of problems here, so you should avoid it.

Another thing to take care of is to make sure your soil is getting proper drainage. Besides having a pot with nice draining holes, you should make sure that the soil itself is well-draining.

If a potting soil is well-draining, that is usually stated on the bag, just pay attention to that detail when you are buying a new bag of fresh and hopefully sterile soil.

Yellow plant mold on soil

If you notice a growth that’s bright yellow, a bit slimy, bubbling, and overall disgusting looking, then your soil has gotten mold contamination by a mold called myxomycete. This mold occurs in places with high levels of moisture and also humidity, so it’s more common when the environment is warm.

As with any other houseplant mold, this one thrives on decaying organic material, so if the environmental conditions are appropriate and you also happen to have some dead leaves lying around on top of the plant’s soil, there’s a risk of this one appearing.

Yellow mold can also occur in greenhouses. This environment is usually very warm, humid, and moist, which are the best conditions to have mold grow.

The yellow mold that appears in the houseplant soil is not dangerous to either people or pets, and it’s also mostly harmless to your plant. You might’ve thought otherwise because a common name for this kind of mold is Dog vomit, but it only gets that because of the way it looks.

Before discussing how you can get rid of mold and also prevent mold, let’s look into identifying yellow mold, as it has different stages of life that are quite different from each other.

Early stage of Yellow Mold: 

The early stage of growth is when this mold has the bright yellow color that it’s known for. It’s usually very moist and full of slime, and if you’re tempted to touch it, do so with a pair of gloves, and very gently because you wouldn’t want to spread more spores around.

Mature stage of Yellow Mold:

After living on your houseplant soil for a few days, the mold will mature and get a pale yellow color. It will lose most of the moisture and it will appear very dry with some cracks on the surface, too.

Final stage of Yellow Mold:

In its final stage, this mold gets dark orange and even brown. The spores are extremely easy to release, and they usually look like dark powder. As the earlier stages are easier to notice, it’s not likely that your houseplant soil will get to this point.

How to get rid of mold that’s yellow

There are many different ways to get rid of mold, so here are a couple of approaches that you can choose when dealing with yellow slime mold.

Leaving it alone

If you leave the plant soil alone to just be, it will probably just disappear after a few days without any visible harm to the plant. However, you or some of your housemates might have allergies that can be triggered by spores present in the air, so it’s advised to remove mold if you notice it.

Remove mold manually

Removing the mold manually is the most simple way to get rid of mold, but you should follow some instructions before you just remove it from the plant soil. If the mold is bright yellow when you notice it, you should wait for a day or two until it gets to its mature stage and becomes pale yellow and cracked.

Once it is mature, you should just get underneath the surface, somewhere around an inch below using some kind of flat support, and then remove debris that’s there.

Use baking soda or apple cider vinegar 

Baking soda has a high pH level, and therefore it’s able to interfere with growth. All you need to do is make a solution containing 1 tablespoon of baking soda and 2 liters of water and put it in a sprayer bottle. Once that’s made, simply spray the solution on top of the plant soil mold, and as soon as tomorrow, it will be ready to be removed.

Another household essential that can be used for mold removal is apple cider vinegar. This acid can also damage mold that grows near house plants because of the different pH levels.

But, as vinegar is not too strong, you can apply it to the top layer of the growth as it is, without making a solution. The mold will be ready for removal the day after.

The main thing to be careful about is to make sure that there are no spores being spread while you remove the mold. To avoid this, just be very gentle and throw away everything in a tightly tied plastic bag. Other plants will probably stay safe, outdoor ones as well as indoor ones.

Green mold on plant soil

If you notice that there’s some infected soil in your potted plants, and the growth happens to be green, that actually doesn’t always have to be mold.

Green growth in potted plants can actually be a variety of things, and besides mold, it also might be algae, or moss.

These might seem like they are completely different, and it might seem weird that they are put together in this one category, however, they have one crucial thing in common.

Algae, mold, and moss will all appear in your potting mix for the same reasons.

Algae is an aquatic plant, and breeding ground for that are places that have a lot of moisture and natural sunlight. The good news is that algae won’t do any harm to the actual plant.

Moss is a type of plant that you’re probably already familiar with. It’s a non-rootimg plant that grows in both indoor potting medium and outdoor gardens.

Moss, as well as algae, won’t do any harm to your plant so you don’t have to worry too much.

Finally, green growth on potting mix can also be mold. Mold usually doesn’t do much harm to a plant, however, it’s best to get rid of mold when you notice it among your plants.

Places that are moist and humid are almost guaranteed to get some growth to occur, if it’s dark it’s probably going to be mold, but if it’s a place that gets a lot of natural light, it’s more likely that you’re dealing with some kind of algae.

Related: Does Potting Soil Go Bad?

Just like they have similarities when it comes to appearing, you can get rid of them using the same resolutions.

Even though neither of these causes real damage to the plants, they spread easily and can infect all the soil in the pot, and then compete for nutrients and moisture with the plant. This will, over time, probably affect the plant’s health.

Listed below are the best and most effective ways to deal with green growth on your plants.

Scrape the growth off

As with previous types of mold, the easiest method is to manually remove anything that might appear on your soil. If this seems like the best solution to you, there are some things to pay attention to.

Firstly, avoid removing the growth with your bare hand, preferably use a spoon or a tool of similar nature. If you think that you’ll do a better job with your hands, make sure to put on a pair of gloves and do everything extremely gently, as you don’t want to spread the spores further in case it’s mold.

Also, it is advised to wear some kind of face and eye protection, just in case you don’t inhale the organic matter. It’s mostly harmless, but you might have some allergies that you don’t know about, so it’s best to be wary. To be sure that you’ve removed all the green material that’s there, remove about an inch of soil from the top of the pot.

Antifungal spray

With all three possibilities, you can use an antifungal spray to help you resolve the problem. While there are antifungal sprays that you can find in a shop, there are things that you can make yourself that can be just as effective.

One option is to simply sprinkle cinnamon powder on top of the growth, as cinnamon is a natural antifungal solution. In about a day, the growth will be killed and ready to be tossed away. Another option is to use a solution made from 1 part baking soda and 9 parts water, and then spray the green matter.

Expose soil to bright light

As moist surfaces are the main base for any kind of green growth to appear, exposing your potted plant to direct sunlight might be the solution for you. But, you need to be careful with this one.

This will work only in case the growth that appeared is mold, because moss and algae actually prefer sunlight to grow. Of course, you will need to be careful if the plant itself is highly sensitive to the sun, as some plants can be.

Repot the plant in sterile soil

If you’ve tried everything and nothing seems to get rid of the growth, then all you have left is to repot your plant. As stated above, before you do this make sure that the soil is sterile as well as the pot.

To sterilize the pot, use a solution made of 1 part bleach and 10 parts water, and let the pot sit in that solution for 10 minutes. After that, just let the pot dry in the sunlight. Make sure that the soil has good air circulation in the new pot, so you can prevent things like this happening again in the future.

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