Yellow Mold In Houseplant Soil? What is it and What to Do?

Yellow fungi on houseplant soil

Have you noticed yellow patches on the soil of your houseplants? Are you worried that this could be a toxic fungus? Here is a detailed article explaining what it is and if you need to really worry about it.

The yellow mold, a mushroom looking that can develop on the garden and houseplant soil is a mushroom called Fuligo Septica or dog vomit slime. It occurs when the soil is kept moist for an excessive period of time. It is of no harm to humans in most cases. However, it needs to be removed to keep your plants healthy.

So what does having yellow mold in your pot plant tell you? And what action do I need to take? Read on to find out more about what to do.

Yellow Mold: What is it and Where To Look At?

Identifying this slime is the first step to learn also how to remove it. This, hopefully, is quite straightforward.

Yellow mold/fungi in soil prevention in houseplant soil
Preventing Yellow Mold Fungus in Plant Soil – Infographic

What is it?

It is commonly (and wrongly) mentioned as fungus, but in reality, it is something different. It is a slime mold (for the expert among you, it is a myxomycete). This is a very simple organism (no brains, no nerves) that, as explained by the University of Wisconsin, it related to seaweed.

Where can you find it?

I found this mold a while ago, growing on top of my mint soil. This is also aligned with what other gardeners found in their potted plants. This is a very bright yellow slime that looks, at a close look, can be either relatively smooth are quite bubbling. It looks frightening, disgusting, and even a bit alien! Check the picture below.

Yellow fungi in soil

Indeed, among gardeners, it is also known as dog vomit slime.

How does it start?

Well, indoors, it is probably your fault.

Indeed, dog vomit slime starts from a high level of moisture and humidity. Indeed, it feeds on decaying organic matter. For you, that means that having a wet potting mix (watering too much) and leaving on the soil organic material (dead leaves, for instance) can trigger the presence of this slime. Having them appear in your potting soil is a clear indicator that it is too wet and that your watering regime may need to be altered.

Another environment indoor in which it can develop is those greenhouses. If you do not provide adequate ventilation molds (among other unwanted problems such as very well water friends)

How do you know if you are watering too much? Well, most houseplants require soil that is moist but not waterlogged (with a few exceptions). Hence, in this case, check it with the finger test (very easy to do, check it out in those tips for growing basil indoors).

How To Identify Dog Vomit (Fuligo Septica)

Early-stage: it appears as a bright yellow patch. This is the way this slime generally begins. It is very moist and compact (you can try to touch with some gloves, but gently otherwise you will spread spores).

Mature stage: after a few days, it matures, and it gets a pale yellow color. It dries out, and you can see some cracks in the surface

Final stage: it gets dark orange, and then finally brown. The spores are easy to be released (they are like dark powder).

When the mold is fully matured and dry, the spores inside are released into the air to spread the mold. So if you see a yellow blob in your pots, as the University of Arkansas suggests, what you probably have is the Fuligo Septica in its very early stages.

Fuligo septica big moving plasmodium

Is Yellow Mold On Houseplant Soil Dangerous?

Yellow mold on soil is not dangerous. Indeed, despite its horrible appearance and name, it is harmless to other living plants, pets, and humans.

But be careful!

The only exception to this would be for people who have allergies. As the mold dries out, the spores are released, and as discussed by the University of Florida, these dusty spores can aggravate people with allergies or can inflame asthma or other respiratory conditions.

For this reason, if you are concerned about the effect on people in your household with these conditions, you have another reason to remove it (after the fact that looks disgusting).

How To Get Rid Of Yellow Mold on Houseplants?

Here you have 3 options to remove this quite disgusting-looking slime.

Option #1: Lazy Approach

If you are willing to be patient, then just leave it alone, Fuligo Septica will likely disappear by itself in a few days. That’s right, there is no need to do anything, of course, unless you are worried about the potential health impacts outlined above.

Option #2: Manual Removal

In this case, go for manual removal. However, you need to wait until it gets pale white and cracked. Its surface will be solid. Then, as shown in the video below, it is a simple matter of getting underneath the surface (half an inch below it would be enough) with thick cardboard or any other flat support you might find at home and removing it.

Slime on Mulch | Yellow Slime on Mulch | How to Get Rid of Slime Mold on Mulch

Option #3: Baking Soda or Vinegar

Baking soda, with its high pH level (opposite of an acid), is able to interfere with the growth of the yellow mold. A water solution of 1 tablespoon of baking soda with 2 liters of water that you can spray on top of the mold. The day after, you can remove it.

Vinegar, for the same reason as baking soda, damage the yellow mold due to its slightly different pH (in this case, acidic). However, given that vinegar is not of a strong acid, it might be a good idea to apply in its pure form (not in a water solution). Again apply once and then the day after it should be dead ready for removal.

As always, when removing, just be careful as some spores might have survived, and you do not want to spread them in your indoor garden (our outdoor).

How to Prevent Yellow Mold From Reappearing?

There are four things you can do to prevent mold from occurring again:

  1. Drying the soil: Allow the top layer of soil to dry out between waterings, which will reduce the moisture level in the soil. This will make sure the soil is a much less hospitable home for mold.
  2. Encourage circulation. This type of mold also thrives in an environment with poor circulation. Hence, if you are growing herbs in a greenhouse, make sure to improve airflow around the plants (at least 20 cm apart) and just place a fan at the slowest speed to bring some new air.
  3. Turning the soil: Rotating the soil when you have the occasion (i usually leave a metal stick on the saucer as a reminder) will improve aeration preventing the soil from holding heat. As a side effect, you also improve the growth of your plant by maximizing the exchange of gases that, in a container, might not happen for the lack of worms and other animals responsible for moving the soil.
  4. No hardwood: Use mulch or potting soil that does not contain hardwood, which is what the mold feeds off. For example, use pine bark, pine straw, or cedar bark.

Can You Reuse a Soil with Yellow Mold?

It is possible to reuse those that have been affected by the yellow mold.

The yellow mold named Fuligo Septica is harmless to your plants as it feeds exclusively on decaying material. For this reason, it is possible to reuse soil that had yellow mold.

Black Spot on Your Basil Leaves?

If you have yellow mold on your soil you can consider yourself lucky. It will not affect your plant. However, if you like herbs like me, you might have other fungi-like an enemy to take care of. If this is your case have a look at the top 5 causes of the most common black spots on basil and many other indoor plants

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