Mycelium Explained: The White Web in Your Soil That Boosts Plant Health

Mycelium Growth, Rosser1954, CC BY-SA 4.0, via Wikimedia Commons

Mycelium in Soil: Nature’s Secret to a Thriving Garden

If you’ve opened a bag of soil from Soil Plus and noticed white strands or patches that look like mold, you might be wondering if something is wrong. The good news is, what you are seeing is not a problem at all. In fact, it is a great sign. That fuzzy white growth is called mycelium, and it plays a powerful role in creating healthy, living soil.

Let’s walk through what mycelium is, what it looks like, why it appears in your soil, and how it can benefit your plants.

What Is Mycelium?

Mycelium is the underground growth of fungi. It is made up of tiny threads called hyphae that spread through soil, compost, wood, and other organic material. You can think of mycelium as the underground network that supports mushrooms. While mushrooms are the fruit of the fungus, mycelium is the main body that does most of the work below the surface.

Mycelium is one of nature’s most important recyclers. It breaks down complex organic material and turns it into nutrients that plants can absorb. It is also part of a communication system among plants that allows them to share resources and protect each other from threats.

What Does Mycelium Look Like?

Mycelium in soil often appears as fine white threads, a fuzzy layer, or a cobweb-like webbing. Sometimes it may look like white mold, which causes concern for customers who are not familiar with it. But mycelium is not mold in the harmful sense. It is a natural part of composting and a sign that your soil is alive and full of microbial activity.

In a sealed bag, where the environment is moist and dark, mycelium can grow more visibly. These conditions mimic the underground forest floor, where fungi thrive. When you open a bag and see white strands, you are seeing a living, breathing soil system at work.

Why Mycelium Is a Good Thing

Mycelium is incredibly beneficial for your plants and your garden. Here are five reasons why its presence is a positive sign:

1. Mycelium improves nutrient availability

Mycelium breaks down organic matter and converts it into nutrients that plants can absorb more easily. It helps unlock phosphorus, nitrogen, and other elements that are essential for growth.

2. Mycelium helps plant roots absorb more

Some types of mycelium form partnerships with plant roots. These partnerships are called mycorrhizae. In this relationship, the fungus helps the plant reach water and nutrients beyond its natural root zone. In return, the plant shares some of its sugars with the fungus. This mutual exchange improves overall plant health and growth.

3. Mycelium supports better soil structure

As mycelium grows through the soil, it binds particles together and creates small air channels. This improves aeration, drainage, and water retention. Healthy soil structure leads to healthier root systems.

4. Mycelium protects against harmful microbes

Living soil is more resistant to disease. Mycelium competes with harmful fungi and bacteria, helping to reduce the chances of root rot and other common plant problems.

5. Mycelium captures carbon

Mycelium plays a role in storing carbon in the soil. This supports long-term soil fertility and also contributes to the global effort to manage carbon levels in the atmosphere.

Is Mycelium Harmful?

Not at all. The kind of mycelium found in bagged or bulk soil is not harmful to humans, pets, or plants. It is a naturally occurring fungus that exists in most outdoor soils. When you see it in your garden soil, it means the soil is active and biologically rich.

You do not need to remove or treat soil that contains mycelium. In fact, removing it would reduce the soil's benefits. We recommend using the soil as it is.

What Should You Do If You See Mycelium in Your Soil?

Nothing at all. Mycelium is a sign of healthy, living soil. Simply mix the soil as you normally would and apply it to your garden beds or containers. The mycelium will continue its work underground, supporting your plants without any extra effort on your part.

If the appearance bothers you or seems too concentrated in one area, you can mix the soil more thoroughly to distribute the growth evenly. Once it is exposed to air and sunlight, the visible strands will usually disappear from the surface.

Why You Might See More Mycelium in Bagged Soil

Bagged soil creates the perfect environment for mycelium to grow. Warm temperatures, moisture, and limited airflow all contribute to the visible growth of fungal threads. Our bagged soil contains organic materials like compost and wood fines, which mycelium naturally feeds on. That is why you may notice it more in bags than in freshly scooped bulk material.

At Soil Plus, we intentionally use composted, living ingredients to provide the best foundation for your garden. Seeing mycelium is simply part of that process.

Changing the Mindset: From Mold to Microbial Magic

We understand that seeing something fuzzy and white in your soil can be surprising. But instead of thinking “this soil is moldy,” we invite you to think “this soil is alive.” Soil is not just a medium for holding plants. It is a living ecosystem, full of fungi, bacteria, and microorganisms that support life from the ground up.

Mycelium is one of the most important parts of that ecosystem. It is not a flaw. It is a feature.

Questions? Let’s Talk

If you ever have questions about your soil or notice something unexpected, please reach out. Our team at Soil Plus is here to help you make the most of your gardening experience. We love soil, and we love sharing knowledge with our customers.

Healthy soil grows strong plants. When you see mycelium, you are looking at nature’s underground helper hard at work. You can feel confident that your soil is doing exactly what it should.