Moldy Potting Soil — Good For Planting?

Last Updated on December 1, 2021 by Grow with Bovees

Are you struggling to get rid of the mold in plant soil? Or are you not quite sure how to get rid of houseplant soil mold and further prevent it from returning?

Worry no more! Read on and let us guide you through all you need to know about this detrimental fuzzy growth in your potting soil.

Let us start off by mentioning that not all mold in plant soil is harmful to your houseplants or outdoor plants.

Saprophytic fungi is one example of a mold that has its benefits for your plant. This mold appears white and fuzzy on the potting soil. It is a naturally growing plant soil fungus and aids in the decomposition of organic matter, which in turn enriches the soil.

This is, however, only one type of mold found in potting soil. In this article we will discuss a few different types of molds, putting focus on how to get rid of them and ultimately, how to avoid them all together.

What Causes Moldy Potting Soil?

Moldy soil is not all that rare and you, as a gardener, might have come across it on more than one occasion.

Main Reasons For Mold Growing On Soil

Mold in general — this includes mold in soil — thrives best in conditions that are moist and humid.

The three main reasons for excessively moist conditions are, as a matter of fact, all human errors. These causes are overwatering, dirty or old potting soil and poor drainage.

Avoid letting your plant sit in a saucer which is filled with water, drain the excess water from the potting soil or empty the saucer that is underneath your plant pot.

Lack Of Air

If you come across mold on plant soil of your indoor plants, this could be blamed on prolonged anaerobic conditions — meaning without air or oxygen. If the soil does not get adequate amounts of air, the growth of mold is encouraged.

Amount Of Light

A lack of light could be another reason. This is mostly relevant for indoor plants.

When houseplants experience a lack of sunlight, their nutrient uptake decreases and the plant is unable to stay healthy and fresh.

White mold on plant soil occurs due to high moisture levels resulting in a lack of sunlight.

To help the plant to dry, place it in an area of bright light or sit it underneath artificial light.

Taking your plant outside for the day is also helpful if you are struggling with mold on plant soil. The fresh breeze and natural light will do it some good.

Using Fertilizer

The use of organic fertilizer may also cause the growth of mold on plant soil. The ingredients that make up organic fertilizer are made up of essential nutrients.

Existing bacteria found in houseplant soil feed on the nutrients and once they start to flourish, white mold starts to form.

Common Types Of White Mold

Believe it or not, there are a lot of varieties of mold on plant soil. By a lot, I mean hundreds. The most common one, however, is the so-called saprophytic mold — also known as white mold.

This type of mold uses carbon that it gets from organic matter found in houseplant soil to grow. There are a few types of white mold that are more commonly occurring than others. Read on to learn about them.


This type of mold is often present in plants, cow dung and houseplant soil. It grows by attaching itself to the harvested grains when the soil gets disrupted. Decomposed organic matter that is rich in sugar and starch makes a great growing ground for mucor mold.

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Aspergillus Sp.

This type of saprophyte mold is mostly found on seeds, grains and in houseplant soil, where it nourishes to grow. The main source of growth for this kind of mold is indoor plants.

This mold has been shown to be quite beneficial to houseplant soil, but be aware that it poses a threat to humans and, in severe cases, may cause respiratory illness.

Trichoderma Sp.

This fungi genus has also been shown to be great for plants. It can be found in almost any houseplant soil and plant structures such as grains and seeds.

This mold thrives well in plants with a lot of roots and is able to prevent harmful fungi from taking over your plant. It also acts as a booster for healthy plant growth.

Other Types Of Mold Spores

  • Sooty mold
  • Gray mold
  • Powdery mildew

The above molds can also be found in potting soil. But these are less common than the saprophytic mold.

Now that we know more about the types of mold found in potting soil, let us go on to the next frequently asked question. Is mold in potting soil harmful?

Is Mold In Soil Harmful?

Most people do not appreciate mold on soil and are in fact disgusted by the sight of it. But is moldy potting soil harmful to your health and to your plant’s health? Continue on to find out.

Is The Mold In Soil Dangerous To Your Plants?

The answer to this question is most often — no!

In fact, fungal and mold spores are present in all types of soil — including houseplant soil — making it part of the plant’s circle of life in nature.

Fuzzy mold and fungi, although not always visible, are actually found in most organic garden mixes. It is how houseplant soil is produced to begin with. Gardeners refer to it as living soil, and they believe that it is the ideal environment for healthy plant growth.

So, hidden houseplant mold or saprophytic fungi in the soil and near the base of the stems is not harmful to your plant.

Saprophytic mold growing in container plants, however, could be a sign that all of your plants’ needs are not being fulfilled. By plant needs we refer to sunlight, moisture and air circulation.

Mold present in your plant pot may also mean that the plant and the mold are competing for food. This is an important fact to remember, as it will affect the growth of your houseplant.

The major problem starts when mold is seen growing on the plant itself, in which case, the health of your plants is being threatened.

This being said, we would advise you to get rid of any mold that you find in the soil — especially white and gray mold — and then work on preventing the mold from coming back by eliminating the underlying problem of why the mold occurred.

Is The Mold In Soil Dangerous To Humans?

The effects of soil mold on humans, is a different story. For sensitive individuals, it may lead to serious issues with health.

It can trigger allergic reactions which present with symptoms such as itchy eyes, skin irritations, congestion and sneezing.

It is also important to note that fungal and mold spores, along with wind or light breezing, may go airborne, which means that they can settle all around your house, making it a much bigger problem than the initial one of just being mold in a pot.

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So, and we will say this again, it is not a great idea to ignore mold growth in plant soil.

Let us go onto discussing a few methods of how you can prevent plant soil mold all together.

Methods To Prevent Mold

Prevention is better than cure, isn’t that what is said?

This is also relevant when it comes to the growth of potting soil fungi.

Soil Sterility

Proper, clean soil is the first thing you need to do in order to prevent mold. The soil that you choose to use should be sterile. But be careful to not believe any claims about soil sterility.

The safest bet is to go about sterilizing your own soil before using it.

There are several methods that one can use to obtain sterile soil. A good one is the oven method.

Add soil to an oven-safe dish that is at least 4 inches deep and then cover the dish with some foil. Bake the soil for roughly  30 minutes at a temperature of 180-200 degrees Fahrenheit until the soil has a temperature of 180 degrees Fahrenheit.

Use a meat thermometer in the center of the soil to obtain the temperature. Be careful that the soil does not reach a temperature higher than 180, this will cause the soil to produce toxins.

When the soil has reached the correct temperature, remove the dish from the oven. Keeping it covered, allow the soil to cool down. And voilà, you have now got yourself some sterilized and safe soil.

Watering Frequency & Moisture

Fungi and mold are very fond of a lot of moisture, soggy soil and overly wet conditions. Excessively damp houseplant soil can easily be prevented by making use of proper watering techniques.

As a rule of thumb, only water indoor plants when the top inches of soil feels dry to the touch. Giving the soil time to dry between watering, will aid in the prevention of soil mold development. Also, ensure that your plant pot has drainage holes.

Adequate drainage will not only prevent mold growth but also help to prevent root rot.

Good Air Circulation

Most houseplants need a decent amount of air circulation in order to grow healthily and prevent mold.

Good air flow also aids in preventing mold growth in potting soil. This is especially relevant for indoor plants, as houses often have a lack of air circulation. It is crucial to make sure that there is enough airflow in the rooms where you decide to keep your houseplant.

Light Is Love

Similar to plants needing adequate air circulation, enough sunlight is also of high importance. Make sure the light also hits the soil, to help prevent mold or fungal development.

Decaying Organic Matter & Organic Material

When you find decomposing plant leaves, non-living organic matter or other organic material, be sure to remove debris immediately to prevent mold from growing.

Decaying plant matter acts as food for mold, creating the perfect breeding ground for gray mold. Also, prevent quick plant mold growth by pruning away any dead parts present in your plant.

Practicing good mold prevention methods will improve your chances of having mold free soil for, hopefully, years to come.

How To Get Rid Of Mold

Once soil mold has developed and made its way to your plant pot, there is unfortunately only one way to get rid of mold and the infected soil effectively, which is by repotting your plant with fresh and sterilized soil.

You might have heard other people say that scraping the visible mold off of the top layer of soil is a sufficient way to get rid of mold.

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These claims are, however, not true. When mold grows, it develops tiny root systems that grow deep into the soil, so scraping off the top layer only makes your plant pot temporarily mold free. You will see the unsightly mold starting to grow again a week or two later.

It is essential to not take the easy way out when it comes to wanting to get rid of moldy soil — that would be a waste of time in our opinion.

When fungal growth is present in your pot, remove the entire plant from its pot, gently tapping off any excess soil from the roots. Rinse the roots and remove mold by cleaning the leaves or areas of the plant where mold has developed.

Then, remove the contaminated potting soil and clean your pot properly, so that there is no more soil stuck to the sides or to the bottom of it. If you want to be sure that all the fungal spores are eliminated, soak your pot in a water and hydrogen peroxide solution for roughly 10 minutes, followed by rinsing the container with regular soap and water.

Lastly, once the plant pot is dry, place some sterile potting soil into the clean pot and replant your shrub in it.

There are other methods that one can try, to get rid of saprophytic fungus, if you do not want to go through the trouble of making sterile soil and replanting your shrub just yet.

Dry Out The Soil

Like mentioned above, mold loves wet conditions and damp soil.

Place your potted plants in the sun, for the soil to dry or remove your plants soil from the pot and spread it out in an area of good amounts of sun. This might be the better option, as most houseplants are sensitive to too much exposure of the sun’s strong ultraviolet rays.

Use A Fungicide

If your potted plant has been attacked by mold, wipe it clean with a moist dish towel of sorts. Then spray it with a bit of fungicide to further protect the shrub.

Using a chemical fungicide is not necessary. Using a mixture of water and potassium bicarbonate is a natural option. This organic fungicide has been shown to work well on white mold. Spray the solution on the top of your potting soil and onto the plant itself to get rid of mold.

Natural Anti-Fungal Options

Mixing natural anti-fungal products with the soil of your potted plant may also aid in moldy situations and contaminated soil. These include baking soda, apple cider vinegar and cinnamon powder. The great thing about these products is that they will not harm your plants.

In Conclusion

All in all, mold in plant soil is relatively easy to control and treat. And getting rid of mold and contaminated soil is not rocket science.

One last word of advice that we can give you when you want to remove mold is, be cautious when using vinegar to treat mold in houseplant soil. Your plant’s root system might not be able to live through its acidity, (some people use vinegar as a weedkiller). If you decide to go the natural route to treat mold contamination, cinnamon or baking soda is a safer option if you want to protect your plant.

Use sterile soil to avoid a mold problem, keeping your plants healthy from the get go. This is the most effective method, and you will not have to go through the trouble of trying to treat and control the fungus.

Happy planting!