Is It Normal for New Potting Soil To Smell Moldy?

Moldy soil is a common problem for those with container gardens, as containers can trap moisture. But what should you do when your brand-new bag of potting soil has a musty, mold-like smell?

It’s normal for New potting soil to have a musty, earthy scent that’s similar to the smell of mold. However, if a recently opened bag of potting soil shows physical signs of mold growth, you’ll need to sterilize the soil before using it. After all, moldy soil can increase the risk of root rot.

This article will address the signs of moldy potting soil and the dangers of using moldy soil. We’ll also discuss ways to sterilize moldy soil, helping you keep your potted plants in tip-top shape!

What Mold-Free Potting Soil Smells Like

Potting soil is typically composed of several elements, including loamy soil, fertilizer, and perlite. These components often emit an earthy, musty smell, particularly when warm. 

If you’ve purchased a bag of potting soil from a local plant nursery or home improvement store and it’s been sitting out in the sunlight, it can release a strong, musty scent when you open the bag.

This smell doesn’t necessarily mean that the soil is moldy, though the smell can be very similar to the scent of mold.

Identifying the Smell of Mold

If you’ve ever been inside an unfinished basement or moldy bathroom, you’re likely familiar with the scent of mold. Most people describe mold’s odor as earthy and stale, much like the scent of wet and rotting wood.

Unfortunately, this smell is almost identical to the scent of fresh potting soil. Therefore, determining whether new potting is moldy by smell alone is practically impossible. Relying on physical indicators of mold growth is the better option.

How To Determine Whether Potting Soil Is Moldy

There are several ways to determine whether mold spores have infested your new bag of potting soil. Some of the most effective methods include:

  • Look for physical signs of mold in the soil.
  • Examine potted plants for signs of mold growth.
  • Use a mold test kit on soil samples.

Let’s discuss these methods in greater detail to ensure you can identify signs of mold in potting soil.

Identifying the Physical Signs of Mold in Soil

One of the most apparent signs of moldy potting soil is physical evidence of mold colonies. For example, if your new potting soil has fuzzy white growths spread throughout it, it’s likely suffering from mold. 

Molds can also appear as white clumps scattered throughout the soil. If your potting soil contains aggregates (like small chalk pebbles), it can be challenging to tell the difference between mold colonies and natural amendments. 

Additionally, some molds are dark brown or black, helping them blend into the soil. But you can also examine recently potted plants for signs of mold growth to determine whether your potting soil is infected.

Signs of Mold Growth on Potted Plants

Slow plant growth or signs of sickness may indicate moldy soil. When mold grows beneath the potting soil’s surface, it can begin to consume the roots of a plant, leaving it looking sickly.

Another common sign of mold damage in plants is yellowing leaves. So, if you notice that your potted plants’ leaves are suddenly wilting or yellowing, mold may be to blame. 

However, overwatering, lack of sunlight, and fertilizer burn can cause plant leaves to be yellow and fall off. For this reason, this symptom isn’t a surefire sign of mold growth. 

Testing for mold is a far more accurate way to determine whether a soil sample has mold spores. 

Using a Mold Test Kit on Soil Samples

If you don’t see mold growth in your new bag of potting soil and you’d like to confirm the absence of mold before planting, you can use a mold test kit to confirm or deny your suspicions. 

Though few mold test kits are available for soil samples, you can repurpose general-use testing kits to test your potting soil. One of the best options (that doesn’t require external lab analysis) is the Mold Armor Do It Yourself Mold Test Kit (available on

This kit contains a petri dish that cultivates mold spores and a sterile swab. You only need to open the petri dish, dip the swab into your potting soil, then push the used tip of the swab across the dish medium. 

Cover the petri dish with the included top, and wait 48 hours. If mold spores are in your potting soil, they’ll begin proliferating in the petri dish. These mold colonies may look white and fuzzy but can also be orange, green, brown, or black.

Of course, you can also take a sample and send it to an independent lab for testing. 

The SEEML Labs Mold Inspector (available on is a fantastic option, as technicians analyze the samples the same day the lab receives them. This kit includes protective gear, including a face mask and a pair of gloves. 

The analysis you’ll receive can offer an in-depth and comprehensive answer to the question, “Is my new potting soil moldy?” Remember, moldy potting soil can be dangerous, so it’s crucial to confirm that your soil is mold-free before using it.

Dangers of Using Moldy Potting Soil

If you think your new potting soil contains mold spores, you’ll likely want to sterilize it before placing it into containers. After all, moldy potting soil has several notable drawbacks, including:

  • Increased risk of root rot.
  • Decreased plant longevity.
  • Reduced indoor air quality.
  • Increased risk of health problems.

Using Moldy Potting Soil Increases the Risk of Root Rot

Root rot is one of the most dangerous threats to plants. It typically occurs when soil drains poorly and retains excess water over time. These damp conditions allow bacteria, fungi, and mold spores to reproduce rapidly.

These harmful elements can then attack a plant’s roots, slowly consuming them. This process causes the rots to root. Because a plant’s roots are crucial to its overall health and longevity, root rot often leads to premature plant death.

Using moldy potting soil can expedite root rot development. However, it can also affect all plant parts, including stems and leaves.

Using Moldy Potting Soil Can Decrease Plant Longevity

Mold spores in your potting soil can reproduce and spread, eventually reaching a plant’s stem and leaves. When this happens, the mold can begin to consume the plant while blocking light, resulting in expedited plant death.

These spores can also enter the air, which is a massive problem for those with indoor potted plants.

Using Moldy Potting Soil Can Impact Indoor Air Quality

Those planning to use potting soil for indoor container plants should take extra caution to ensure their soil is mold-free. After all, mold-filled potting soil can negatively impact indoor air quality. 

Your home’s indoor air quality can significantly influence your health. For example, indoor air full of pollen or mold spores can be harmful, especially over prolonged periods. It’s even possible to develop respiratory problems when exposed to airborne mold.

While an air purifier can help rid your home’s air of many pollutants, it’s fighting a losing battle if you don’t tackle the source of the mold.

Using Moldy Potting Soil Can Cause Health Problems

Coming into contact with mold can be dangerous, particularly for those with asthma or immunocompromised. 

Though mold in potting soil may not be exceptionally hazardous to human health in outdoor containers, it can be problematic when you use it indoors. After all, airflow is restricted in indoor environments, increasing the chance of breathing in mold spores.

Common health problems associated with mold exposure include:

  • Sneezing.
  • Coughing.
  • Fatigue.
  • Difficulty breathing.
  • Headache.

Besides, mold spores in indoor potting soil can spread to other areas of your home via your skin, clothing, or HVAC system. These spores can lead to rapid mold growth in kitchens and bathrooms. 

Because mold remediation services can be expensive (typically costing thousands of dollars), it’s often best to sterilize moldy potting soil before using it.

How To Sterilize Moldy Potting Soil

If you notice signs and symptoms of mold in potting soil, it’s crucial to sterilize that soil as quickly as possible. After all, mold can proliferate in potting soil, leaching it of its nutrients and becoming more hazardous to handle.

Fortunately, there are several ways to sterilize moldy potting soil to make it safe for indoor or outdoor use. Some of the most common methods include:

  • Baking the soil.
  • Microwaving the soil.
  • Boiling the soil.
  • Exposing the soil to harsh sunlight.

If you’d like to learn more about these sterilization methods and how they work, check out my other article: How to Disinfect Root Rot Soil

Final Thoughts

New potting soil has an earthy, musty smell that’s very similar to the smell of mold. But unless you see physical signs of mold growth, it’s unlikely that the soil is moldy. Still, it’s an excellent idea to examine potting soil thoroughly before pouring it into sterile containers.

Moldy potting soil can shorten a plant’s lifespan and cause root rot. It can also lower indoor air quality and contribute to health problems. Fortunately, there are several ways to sterilize moldy potting soil, making it safe for indoor and outdoor use.

You can read my in-depth guide on whether moldy potting soil still is usable here: Your Bag of Potting Soil Is Moldy: Is It Still Usable?

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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