How to treat Soil mold

Finding a strange growth on your plant's soil can be alarming, but don’t panic. The vast majority of mold and fungi found in houseplant soil are completely harmless to your plants.

What is soil mold?

Soil mold is a general term used for many different types of fungi that grow in potting mixes. The vast majority of these molds feed on dead and decomposing materials in the soil, helping to break them down into nutrients.

Because mold spores exist naturally in the air and are already present in the soil when you buy it, avoiding them entirely is more or less impossible. However, large blooms and sudden outbreaks typically mainly happen if:

• The soil is constantly moist

• You've recently repotted - Fresh potting soil is rich in organic matter, which can trigger a temporary mold spike for a number of months.

• You use certain organic fertilizers - Products containing materials that aren't fully broken down yet (like compost, kelp, or bone meal).
  

Symptoms

Because soil mold behaves differently depending on your home's environment, you can identify its presence by checking for some key signs:

• Appearance - Look for a fuzzy, velvety, or slightly slimy layer sitting on the soil surface. It most commonly appears as a white fuzz, but it can also turn yellow, brown, or gray.

• Location - While it typically carpets the top layer of soil, it can also peek out of the bottom drainage holes or form a powdery crust on the outside of porous terracotta pots. You might also spot it clinging to fallen, dead plant debris like wilted leaves.

• Odor - Affected soil can give off a faint damp, earthy smell.

Soil mold itself will not cause any symptoms on the plant. If your plant is drooping, wilting, or turning yellow for example, those are usually signs of overwatering or root rot, the underlying conditions that allowed the mold to thrive in the first place, rather than issues caused by the mold.

What to do now

Because soil mold is so common and harmless, you technically don’t have to treat it. However, if the fuzzy look bothers you, here is how you can manage it:

• If you recently repotted your plant, wait for it to disappear on its own. The mold is likely just enjoying the fresh nutrients. It will usually burn through its food supply and disappear on its own after a couple of months.

• Let the soil dry out to the recommended level for your plant before watering again. If the app ever suggests watering while the soil is still too wet, snooze the task.

• If you noticed a mold outbreak after using an organic fertilizer, temporarily swap it out for a mineral fertilizer to stop feeding the fungus.

• (Optional) Remove all visible mold on the surface, especially if you have very dense mold growth. But note that it will likely regrow again as you expose new fresh soil for the mold to grow on.

• Add beneficial bugs like springtails, which naturally eat mold. You can often find them in your other houseplants, in outdoor compost, or buy them as starter cultures from terrarium shops.

Common questions

Why is mold developing in my soil?

Mold is almost always present, and start growing when the conditions are right. It loves organic matter. Soils that are rich in organic components (like compost or peat moss) are more likely to host fungi. This is why you rarely see mold in sandy, mineral-heavy mixes, such as cactus and succulent soil.

How can I prevent this from happening again?

Soil mold can't always be fully prevented. But monitoring the soil moisture level and making sure the soil dries out to the recommended level in between watering your plants is most important. Don't change the soil more frequently than necessary, and consider using a mineral fertilizer for a while.

Can soil mold cause other problems?

It’s actually the other way around! Soil mold won’t harm your plant. It only eats dead organic matter. Never your living plant. A little mold doesn't automatically mean something is wrong. A small amount of mold just means you have healthy, active soil breaking down nutrients. Especially after a recent repotting or fertilizer swap.

Because mold loves moisture, a massive outbreak can sometimes be a secondary symptom of overwatering. While the mold itself won't hurt anything, soggy soil can cause root rot, so it's a good reminder to double-check your drainage. If your plant shows signs of stress, there's something else going on rather than just the mold.

Common Look-Alikes

There are a few common growths that can be confused with soil mold. Fortunately, none of these are directly harmful to your plants either.

Mycelium

Fungal mycelium is commonly seen in the soil of houseplants. It is typically white or yellow and can sometimes form small, egg-like or ball-like structures, with actual mushrooms developing at a later stage.

These fungi feed on decomposing organic material in the soil, not on your living plant.

No action is usually necessary. However, you can pluck out any actual mushrooms that form to prevent them from releasing spores and spreading to other pots.

Algae Growth

This often appears as a dark green to black, slimy coating on top of the soil or on the outside of clay pots.

Algae require consistently wet or damp conditions to thrive, making them almost inevitable when you are growing plants that need constantly moist soil.

Algae generally don't require treatment. However, if the growth becomes thick enough to act like a "lid" and reduce soil aeration, it is a good idea to scrape off the top layer.

Moss

Moss can be highly decorative. Just like algae, it primarily grows on soil that stays constantly moist and in environments with high humidity.