Is Moldy Potting Soil Safe To Use?

Everything is good until you wake up one morning to find your favorite potted plant covered with fuzzy, white mold. But you don’t need to panic, that is most likely a harmless saprophytic fungus.

In this article, you’ll discover whether or not to be concerned, how to eradicate the mold organically and safely, and a few preventative measures you can take to ensure it doesn’t return. It is a simple and painless operation for both you and your plants.

Is Moldy Soil Harmful To Plants?

The short answer is that the white stuff growing in your potted plants is unlikely to harm them. Molds and fungus are present in every organic gardening mix, even if they are not always visible. Indeed, many organic gardeners feel that “living soil” provides the best environment for growth. So it’s a sign of life, though it’s not one you’d want to look at since it’s not that attractive.

Saprophytic fungi are caused by compost fungi, which can naturally occur in plants, and it can be beneficial to plants because it aids in the decomposition of non-living organic materials, which enriches the soil.

But it could, however, indicate that your plant isn’t getting enough sunlight, air circulation, or moisture, because the mold may be fighting for nutrients with your plant. So, this is also a warning indicator that you should be aware of.

Most Common Types Of Potting Soil Molds

There are hundreds of distinct forms of molds; however, saprophytic mold, sometimes known as white mold, is the most frequent one found in potting soil. Saprophytic mold absorbs carbon from organic debris, which it then uses to grow.

The following are the most prevalent saprophytic molds:

  • Mucor
  • Penicillium sp.
  • Aspergillus sp.
  • Trichoderma sp.


Mucor is a type of mold that is widely found in soil, plants, and cow dung. It grows by harvesting the grains that are gathered when the soil is disturbed. It thrives on degraded organic debris, particularly those high in starch and sugar.

Penicillium sp.

Penicillium mold grows where there is enough humidity and the environment is damp, which is why it is usually seen in potting soil. Penicillium sp. is a common soil fungus that spreads quickly in nature via soil and air. One thing to keep in mind though is that according to research when Penicillium sp. comes into touch with a plant’s roots, it can help improve the plant’s development.

Aspergillus sp.

Saprophytes are usually found in soil, seeds, and grains where it thrives. This mold’s principal source of development is indoor plants. While this mold is beneficial to soil, it is exceedingly dangerous to humans and can cause a variety of respiratory problems. So be cautious.

Trichoderma sp.

Trichoderma is a fungus genus present in practically all soil and other plant parts such as seeds, grains, and so on. This mold feeds when there is a high level of plant roots present. Furthermore, it also stops other harmful fungi from attacking the plant and promotes plant growth.

Other molds found in potting soil include sooty mold, grey mold, and powdery mildew, but they are not very common.

Now that you’ve learned about the many forms of molds, let’s look at why your potting soil might have mold on it.

Why Has Your Potting Soil Become Moldy?

White mold, which thrives in damp and moist circumstances, is the mold you see on your potting soil. This could be due to overwatering, insufficient drainage, or using outdated or impure potting soil.

The appearance of mold on your indoor plant’s potting soil could be caused by anaerobic circumstances, which means that the soil isn’t getting enough air, which favors mold growth.

Another possibility is a lack of sunlight. When indoor plants do not receive enough sunlight, they are not getting enough nutrients to stay fresh and healthy. Inadequate sunshine creates damp and moist conditions that encourage mold growth.

Another probable cause of mold is the use of organic fertilizer in your potting soil. The fertilizer’s content includes all of the necessary nutrients for the existing bacteria to thrive. When bacteria begin to multiply, it produces white mold.

What Happens If You Have Mold In Your Potting Soil?

Having mold on potting soil isn’t always a bad thing. It does not harm the plant, but it may indicate that the soil is not receiving the nutrients it requires to thrive.

However, this does not mean you may continue to use moldy potting soil. It is preferable to remove the mold because it will eventually impact your plants, causing the leaves to become yellow, droop, or die.

Mold can harm both indoor and outdoor plants because it emits spores that are carried by the wind and can contaminate other plants. The good news is that you won’t have to throw away your plants because the mold can be easily removed.

How To Get Mold Out Of Soil

Here’s what you can do if mold is forming under your houseplants, or in any container plant for that matter:

1 – Place them in direct sunshine. Before you do anything else, place the plants in a location where they can get lots of sunlight and fresh air. If the mold is in its early stages, it will most likely disappear if exposed to enough air and sunlight.

2 – Physically remove the mold. Scrape off and remove the damaged soil while wearing a respiratory mask.

3 – Dust the dirt lightly with ground cinnamon. Cinnamaldehyde, the compound that gives cinnamon its flavor and fragrance, is an excellent natural fungicide that inhibits mold growth. Try to create a uniform distribution and keep in mind that a thin layer is all that is required.

4 – Water only when the top two inches of soil are dry. Wait until the top quarter-inch of a smaller container has dried before returning to a water regimen. To check the moisture level, use your finger.

5 – Repot the plants. Another successful way is to remove the plants from the container and replace the moldy soil with fresh and pure potting soil, and while you’re doing it, clean the pot thoroughly to ensure no sign of mold remains. After repotting the plants, establish an effective care regimen to prevent mold regrowth.

6 – Make use of a fungicide. After you have attempted all the previous steps, you can use a fungicide to eradicate any remnants of mold that remain in the roots. If you want to avoid chemicals and go for a more natural solution, mix Potassium Bicarbonate with water.

Is There Anything Else You Can Do?

  • Never leave pots in saucers of water for longer than five minutes. Remove any excess moisture.
  • To assist plants dry, place them in direct sunlight or a bright artificial light.
  • After exposing indoor plants to natural light and air for at least a day, find a new location inside the house that is a little more sunny and breezy.
  • When repotting make sure the new pot has enough drainage holes.

Is it OK To Use An Old, Moldy Bag Of Potting Soil?

When you don’t use all of the potting soil at once, you may notice that fuzzy white stuff has sprouted inside the bag when you go to use some more. It’s also possible that you bought a new bag of potting soil, brought it home, and discovered the same thing. The question is, should you still use that soil?

  • Yes, if you’re transplanting, planting, or simply replenishing dirt levels. Simply mix the contents of the bag and massage the white stuff back in with the black stuff before using it. You could also add some fresh compost. Cut the bag open and let it outside for a day or two, exposed to the sun and air, turning occasionally. You could also add some new compost to it.
  • However, if you intend to sow seeds, you should not utilize that soil, because the mold will compete for nutrients with the seedlings. It’s ideal to give the new plants a fighting chance in some fresh soil.

Is The White Stuff Growing In Your Potted Plants Toxic To Humans?

When we see mold, most of us will cover our mouths and flee in the opposite direction. However, despite what most mold-removal businesses will attempt to convince you of, the mold in your potted plants is not very toxic to humans. However, if you are very allergic to mold, you may not want to take any chances, since according to some, the spores can cause allergic reactions.

How To Prevent Mold Growth In Your Soil?

Mold can never be completely removed. Mold spores are a natural component of soil and are usually harmless. Heat, humidity, and a lack of ventilation are the major hazards to your plant. Mold spores evolve into adult fungi and produce even more spores under these conditions.

Because they retain more moisture, indoor planters and container gardens are the most popular hosts. Here are some simple steps you could follow to avoid mold growth:

  • Don’t overwater your plants. Mold growth in container plants is primarily caused by overwatering. Happy spores are far more likely to be found in soil that is consistently moist. Water only once a quarter of the total soil volume in the container has dried out. For example, if your plant’s soil is 8″ deep, wait until the top 2″ have dried out before watering. Watering most indoor plants once a week should suffice.
  • Reduce the humidity and increase the ventilation. These two circumstances, when combined, produce a stale environment in which mold thrives. You’re already reducing humidity by not overwatering, but to reduce moisture even more, place your plants in brighter, well-ventilated areas or use a small fan to regularly pump new air around the soil.

Final Thoughts

Overall, mold in potting soil is a simple problem to solve. An extra piece of advice is to avoid using vinegar since mold can withstand acidity, but your plant’s roots might not. Cinnamon is a lot safer and more effective alternative.