As a gardener, there’s nothing quite like the thrill of seeing your plants thrive. But sometimes, we stumble across something unknown: a white substance on the ground or the roots of plants. It may raise a silent alarm—is it mold? Is it toxic? Could it be an indication that your garden is booming?
In most instances, this elusive white growth will be mycorrhizal fungi or white mold. To the untrained eye, they are often quite convincing at first sight as being almost the same. However, what they do to your plants is the opposite. One is the gardener’s best friend. The other was the unwanted guest. So how do you know which they are?
Let’s examine each one, how they look, and their main differences to accurately diagnose what’s happening in your garden soil and how to react accordingly.
What Is Mycorrhizae?
Mycorrhizae (the plural form of mycorrhiza) are fungi beneficial to plants and enter into a symbiotic relationship with the roots of most plants. The term is derived from the Greek words mykes (fungus) and rhiza (root), and that’s precisely what these fungi are—root fungi.
These fungi, invisible to the naked eye, infest plant roots and push their system into the surrounding soil, creating a delicate web-like substance called mycelium. The system functions like a longer root system, enabling plants to uptake more water and nutrients—primarily phosphorus and nitrogen—that may otherwise be out of their grasp.
In return, the plant supplies the fungi with sugars and carbohydrates, thus making this a win-win relationship. This subterranean association has existed for over 400 million years and is vital to plant health, soil fertility, and ecological balance.
What Does Mycorrhizae Look Like?
To the naked eye, mycorrhizal fungi can resemble a fine, white, cobweb-like growth in or around the root zone. It may even coat parts of the soil surface in container plants or raised beds, particularly in moist environments.
Some key signs that you’re looking at mycorrhizae:
- A light, webby network around the roots or just under the surface
- No visible plant damage
- Healthy, growing plants nearby
- The white material has no objectionable odor
- It doesn’t spread quickly or go wild topside
Don’t worry – not all mycorrhizal interactions are visible, particularly in sand or well-draining soils. However, you may observe it more clearly in rich, damp, organic material such as compost or coco coir.
What Is White Mold?
White mold, alternatively, is a fungus infection that harms numerous plant species, especially vegetables such as beans, lettuce, and tomatoes. Also referred to as Sclerotinia sclerotiorum, this mold could easily spread and, left unchecked, result in rotting, wilting, and death of the plant.
White mold grows best in wet, humid, and poorly ventilated conditions. It is not opportunistic like some beneficial fungi, such as mycorrhizae, and instead feeds on the rotting tissue of your plants.
How Does White Mold Appear?
White mold most commonly appears as:
- A white, fluffy, cottony growth on stems, leaves, or soil
- Its rapid growth can cover the soil and up plant stems
- Black sclerotia (hardened spores) present that look similar to rat feces
- Yellowing, wilting, or collapse of the infected plant
- Soft, mushy tissue beneath the mold
- It’s not cosmetic—white mold kills the plant by cutting off nutrient flow, and in later stages, it can take over a whole garden bed.
Mycorrhizae vs. White Mold: The Major Differences
Let’s compare them side-by-side:
| Feature | Mycorrhizae | White Mold |
| Appearance | Thin, web-like; often in soil or around roots | Fluffy, cotton-like growth on stems, leaves, or soil |
| Texture | Fine and thread-like | Thick, cottony, and soft |
| Smell | Neutral, earthy | May smell musty or foul if decay is present |
| Plant Health | Promotes plant growth and root development | Causes plant rot, wilting, and death |
| Growth Pattern | Slow and steady; mostly in root zone | Rapid and aggressive; spreads across surfaces |
| Habitat | Healthy, well-aerated soil with living roots | Moist, humid environments with plant decay |
| Treatment Needed? | No; it’s beneficial | Yes; requires removal and treatment |
How To Know Which One You Have: White Mold Or Mycorrhizae
Here are some useful tips to determine what you’re dealing with:
Inspect your plants’ health: If your plants appear healthy and robust, the white material is probably mycorrhizae.
Examine the position: Mycorrhizae would be close to the roots or below the ground. White mold extends onto the stems and leaves above the ground line.
Smell the area: A pungent, musty, or rotting odor indicates mold rather than beneficial fungi.
Test moisture and airflow: Low airflow and high humidity incubators white mold.
Watch growth rate: Mycorrhizae grow slowly. Under favorable conditions, white mold can develop and spread in a day or two.
How To Control Mycorrhizae And Eradicate White Mold
Mycorrhizae need careful management to flourish as healthy partners in plant development. White mold on plants is an offending fungus that requires early identification and control.
Encouraging Mycorrhizae
If you’ve confirmed that it’s mycorrhizae, congratulations—your soil is alive and thriving! To support these fungi:
- Don’t over-till the soil
- Limit synthetic fertilizers, particularly high-phosphorus
- Use compost and organic matter
- Don’t use fungicides unless needed
- Plant a variety of different species to encourage fungal networks
Getting Rid Of White Mold
If it’s white mold, this is what to do:
- Pull out affected plants at once
- Increase air movement around plants (prune, space, ventilate)
- Avoid overhead watering and water at the soil line
- Apply a fungicide if necessary (preferably organic)
- Practice crop rotation to reduce pathogen buildup
- Sterilize tools and containers to prevent the spread
Prevention Tips
Regardless of what you’re dealing with, healthy soil practices go a long way in creating an environment that favors beneficial fungi over harmful pathogens. Here are pretentative measures for mold-free soil:
- Don’t overwater—water deeply but less frequently
- Use mulch to retain soil moisture without creating a humid surface layer
- Promote biodiversity in the garden
- Check your plants regularly for signs of trouble
Last Thoughts
Knowing how to differentiate between mycorrhizae and white mold can save your plants—and your sanity. What may appear to be a damaging mold may be nature doing something beneficial for you, creating a hardy underground web to feed your plants. On the other hand, catching white mold early on can forestall the type of garden catastrophe nobody wants to deal with.
Always look closer before you leap. Sometimes, white fuzz is just a friend in disguise.
Frequently Asked Questions
Can mycorrhizae grow on top of the soil?
Mycorrhizal fungi may occasionally appear on the surface in high-humidity environments, particularly in pots or containers. It’s generally harmless and an indication of healthy microbial activity.
Is white mold dangerous to humans?
White mold in the garden is not usually dangerous to humans, but extended exposure to mold spores can aggravate allergies or asthma in susceptible people. Always use caution.
Can I treat white mold with natural products?
Yes! Neem oil, garlic sprays, and baking soda solutions can control white mold in its initial stages. Provide good air circulation and remove any infected plant material.