What Is Snow Mould? Causes, Identification, and What to Watch For

As winter fades and the snow begins to recede, you might expect to see a green lawn emerging. Instead, many homeowners are greeted by a startling sight: patches of grass covered in what looks like spiderwebs or white cotton.

Every spring, as the snow melts, we get calls from homeowners asking, what is snow mould because they assume their lawn didn’t survive the winter. What they’re usually seeing is snow mould.

Snow mould is a cold-weather lawn fungus that shows up right after snow melts. It looks like gray, white, or pinkish patches of matted grass. It thrives in areas where snow sat for a long time, especially when the ground wasn’t fully frozen underneath.

How to Identify Snow Mould

The good news is it looks worse than it actually is in most cases. While it can look alarming, it is primarily a cosmetic issue for most residential lawns and rarely causes permanent damage. Identifying it correctly is the first step toward helping your lawn recover.

This is the hallmark sign of snow mould, a fungal disease that thrives under snow cover and becomes visible during the spring melt.

Visual Signs of Snow Mould

The most distinct characteristic of snow mould is its texture. It often resembles a fine, cobweb-like netting or a cottony mass resting on top of the grass blades. This fungal growth, known as mycelium, can look like a “matrix” or webbing that mats the grass down.

Key identification features include:

• Circular Patches: The damage typically appears as circular areas of straw-colored or bleached grass, ranging from a few inches to several feet across.
• Webbing: In wet conditions, you may see white, gray, or pinkish fungal threads stretching across the affected leaves.
• Matted Texture: The grass within the patches often appears crusted or glued together, preventing new growth from pushing through.

Where and Why Snow Mould Forms

Snow mould is caused by a lack of air circulation under the snow layer. It is most prevalent in areas where snow piles up deeply or remains for long periods, such as:

• Depressions, swales, or low spots in the yard.
• North-facing areas where snow melts slowly.
• Along driveways or walkways where snow is piled during shoveling.

The condition is often exacerbated by leaves left on the lawn over winter, which trap moisture and further inhibit air movement. Additionally, heavy applications of nitrogen fertilizer late in the fall can promote succulent growth that is more susceptible to infection.

Susceptible Grass Types

Not all grass species react to snow mould in the same way. The severity of the infection often depends on the type of turf you have.

Golf courses often struggle more with snow mould because they rely heavily on bentgrass and annual bluegrass, which are prone to significant damage. Most residential lawns containing a mix of bluegrass and fescue will typically recover on their own.

The Two Main Types of Snow Mould

While “snow mould” is the common term, there are actually two distinct fungal diseases that affect lawns in cold climates. Both thrive in similar environments but have different scientific names and slightly different appearances.

1. Gray Snow mould (Typhula blight): This variety is characterized by white-to-gray fungal growth. It often produces small, hard, grain-like structures called sclerotia on the infected leaves.
2. Pink Snow mould (Microdochium patch): As the name suggests, this type often has a pinkish tint to the fungal mycelium, especially at the outer edges of the patch. Unlike gray snow mould, it does not produce sclerotia and can remain active even without snow cover if the weather is cool and wet.

Pink vs. Gray: Which Spreads Faster?

Not all snow mould behaves the same way. The two most common varieties – Gray Snow mould (Typhula blight) and Pink Snow mould (Microdochium patch) – have different spreading habits.

Why Is Snow Mould Growing On My Grass?

Snow mould growth usually occurs for two reasons:

The main reason, with lots of snow and the up and down of melting, you will accumulate a layer of ice under the heavy snowbank, (the greater the weight of snow, the greater the weight of ice underneath) this often makes the grass blade tissue more prone to snow mould.

The second reason, if the grass is more lush underneath, (from being taken care of well) meaning there is more nitrogen in the leaf blade, then it will be more susceptible to snow mould.

But this is also the reason why it appears more pronounced when contrasted against your greener lawn. It is also why your lawn will green up even quicker this spring since the nutrients are already there!

How Do You Prevent Snow Mould?

There are a number of tasks you could do to your lawn to prevent snow mould. These should be done in the fall before any snow accumulates.

Mow your lawn before winter sets in. (should be 2.75 inches)

• Long grass blades will bend and fold during the winter as the snow piles on top of it. The folded grass will trap moisture and accelerate the growth of snow mould. Mowing your lawn below 2.75-3″ should help to prevent the fungus from growing.

Rake leaves and other debris off the lawn before snowfalls.

• • Leaves and debris in your lawn will trap moisture and prevent the snow from melting as quickly. Freeing up your lawn will help prevent snow mould from growing.

Snow Mould (mold) combined with dog damage on a home lawn

Sometimes it’s not just snow mould.  In the 2nd picture, they also have a dog that has been doing its business on top of the snow, mainly in one section of the lawn.

* Dog and Pet damage compound the problem by adding a higher level of salt to the soil in a concentrated location.  This can be remedied with a specialized application from your LawnSavers professional!  In addition, it is important to rake these areas out thoroughly and to dilute the area with extra watering as soon as possible to flush and spread the salt concentration so grass can regrow.

Will Snow Mould Spread?

Snow mould is a fungal disease that can aggressively spread across your lawn under the right conditions, turning a pristine yard into a patchwork of matted, discolored grass.

While it typically thrives beneath a blanket of snow, the fungus can continue to expand its territory even after the snow melts if cool, damp weather persists. Understanding how this disease travels, and when it stops, is critical for protecting your turf from lasting damage.

How Snow Mould Spreads

Snow mould spreads primarily through the growth of mycelium, which are thread-like fungal structures that move from plant to plant under the cover of snow or wet leaves. The disease does not require a host to move; it can expand outward in circular patches as long as the environment remains favorable.

The spread is driven by specific environmental factors:

• Lack of Air Circulation: A heavy layer of snow or ice prevents oxygen from reaching the turf, creating a stagnant environment where fungi thrive.
• Moisture and Temperature: The pathogen is most active in temperatures between 32°F and 60°F (0°C – 15°C) when the ground is unfrozen but wet.
• Physical Transport: Spores can be spread by wind, rain, and human interaction, such as walking on infected grass or using lawn equipment that hasn’t been cleaned.

How to Get Rid of Snow Mould and Stop the Spread

Many people search “how to get rid of snow mold“, the most effective way to halt the spread of snow mould is to alter the environment so the fungus can no longer survive. Remediation focuses on drying out the turf and encouraging new growth, and this is typically how to get rid of snow mould.

1. Encourage Air Circulation: Once the snow has melted and the ground is dry enough to walk on without leaving deep footprints, lightly rake the matted grass. This breaks up the crusty fungal layer and allows air to reach the soil.
2. Apply Nitrogen: A light application of nitrogen fertilizer in the spring helps the grass “outgrow” the disease by pushing new leaf tissue that replaces the damaged blades.
3. Manage Fall Debris: Prevent future outbreaks by mulching leaves and cutting grass shorter (around 2 inches) before winter to reduce the trapped moisture that fuels fungal growth.

“The easiest way to get rid of snow mould is to allow for air circulation… it will outgrow the snow mould before it causes damage in terms of turf death.”

Can You Get Snow Mould Without Snow?

It sounds like a contradiction in terms, but the answer is yes, you absolutely can get snow mould without a single flake of snow on the ground. While the name suggests a winter-only problem, this fungal disease is better defined by the cool, wet conditions that allow it to thrive rather than by the snow itself.

If you are seeing circular patches of matted, discolored grass in your lawn during cool, damp weather, you might be dealing with “snow mould” regardless of whether you’ve had a white winter.

The Short Answer: Yes (But It Depends on the Type)

To understand how this disease strikes without snow, you must distinguish between the two primary types of snow mould. While they are often grouped together, they behave differently regarding their environmental requirements:

• Pink Snow mould (Microdochium nivale): The culprit responsible for infections without snow cover. It does not require snow to develop and can be active in cool, wet weather with temperatures ranging from 32°F to 60°F (0°C to 15°C). Because it thrives in these “cool and damp” conditions, it is technically classified as Microdochium patch when it occurs without snow cover.
• Gray Snow mould (Typhula spp.): This variety is a “true” snow mould. It typically requires an extended period of snow cover – usually at least 60 days – to develop significantly. The snow acts as an insulator, trapping moisture and maintaining the specific temperature just above freezing that this fungus needs to grow.

Conditions That Cause Snow Mould Without Snow

If you haven’t had snow but are still seeing damage, your lawn likely provided the perfect breeding ground for Pink Snow mould through other means. The disease takes hold when moisture gets trapped against the leaf tissue for prolonged periods.

Common non-snow triggers include:

• Cool, Wet Weather: Extended periods of drizzle, fog, or high humidity in late fall or early spring can trigger outbreaks even in the absence of snow.
• Leaf Accumulation: A layer of unmulched leaves left on the lawn over winter creates a “wet blanket” effect. This traps moisture and prevents air circulation, mimicking the conditions of snow cover.
• Poor Drainage: Low spots in the yard (depressions) where water collects and creates persistent dampness are prime targets for infection.
• Lush Growth in Late Fall: Applying heavy nitrogen fertilizer too late in the season can promote succulent grass growth that mats down easily, creating a dense canopy that traps moisture.

Does Snow Mould Smell?

While the visual damage to the grass is obvious, many people are caught off guard by the odor. Yes, snow mould does smell.

The scent is often described as a pungent, musty odor that rises from the lawn as the snow recedes. This smell is a direct result of the fungal activity occurring beneath the snow, where decaying organic matter and a lack of oxygen create the perfect breeding ground for disease.

The Scent of Decay: What Does Snow Mould Smell Like?

The odor associated with snow mould is distinct and unpleasant. It is typically characterized as a strong, earthy, or rotting smell. Some experts have even described the scent as a cross between “old running shoes” and an outhouse.

This odor occurs because snow mould is essentially a rot. The fungus thrives on decaying leaf tissue and grass blades that have been trapped under a layer of ice or snow without air circulation. As the fungus digests this organic material, it releases gases that contribute to the “mouldy” smell that permeates the yard during the spring melt.

Can Snow Mould Make You Sick?

Beyond the unpleasant smell, snow mould can pose health risks for humans and pets. As the snow melts and the fungus dries out, it releases spores into the air.

Breathing in these spores can trigger allergic reactions similar to seasonal hay fever. Common symptoms of snow mould allergies include:

• Sneezing and runny nose
• Itchy, watery eyes
• Congestion and coughing
• Worsening of asthma symptoms

While there is no evidence suggesting snow mould is toxic to dogs if ingested, the spores can cause respiratory irritation in pets just as they do in humans.

What Snow Mould Means for Your Lawn in Spring

While the sight of “spiderwebs” on your lawn can be unsettling, snow mould is a common and manageable condition.

By recognizing the signs early – circular patches of matted, cottony grass – and taking simple steps like raking to improve air circulation, your lawn can bounce back quickly as temperatures rise.

Here’s the key thing we tell customers every spring: Don’t panic.

Most snow mould damage is cosmetic and temporary. Once the lawn dries out and gets some air movement, it starts to recover on its own. The biggest mistake we see is people overreacting too early, raking aggressively when the lawn is still wet, or assuming they need to replace everything. In most cases, a bit of patience and the right approach to lawn care in Spring is all it takes to bring it back.

How Do You Treat Snow Mould in Toronto?

Like all lawn fungal diseases, you can apply a fungicide (for snow mould this would be done in the Fall). However, in our experience, the prevention of snow mould by regular lawn maintenance is the best option.

Will My Grass Recover From Snow Mould?

Yes, your grass will usually recover just fine. It doesn’t normally kill the grass as the mould does not affect the roots of the plant.

In the Spring, when the grass is relatively dry and not frozen on the surface; just lightly rake the grass to lift up the blades a bit to allow air circulation. The situation normally resolves itself as the grass starts to grow with warmer temperatures.

It doesn’t normally affect the roots, just the leafy tissue on the surface. It usually looks like a bit of a fuzzy web-like mass is growing on top of the blades. These are mycelium that are part of the fungus. You’ll notice it’s usually on the areas where the snow was slower to melt. Make sure to mow your lawn between 2 3/4″-3″ before winter sets in. Be sure to rake leaves and other debris off the lawn before snowfalls. It doesn’t normally kill the grass. Re-seed with cultivars of grass-like LawnSavers custom blend which contain varieties of seed that are bred to be resistant to this fungus.

The good thing is that it’s only superficial and just requires a very light raking with a leaf rake to allow air penetration through the lawn.  The well-nourished plant will grow through this with new leaf tissue.

Aerating and OverSeeding, as well as a balanced and well-fortified slow-release fertilizer, will make all the difference

So in short, snow mould is nothing to worry about.  A light raking and those areas will more than likely disappear as soon as the soil warms up and the grass starts to grow!

Use our month-by-month lawn care calendar to get the growing season off to a good start.
Start whenever it’s above 10 deg C outside and the lawn is not too wet.

I hope this helps,

Kyle!