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Snow Mold

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Posted on: Mar 01, 2023Raunie

The weather is warming, the snow is melting, and it looks like Spring is well on its way. While the weather brings excitement with the ability to soon get outside and begin our season, with every change in season comes different challenges for lawns and maintaining them. Some challenges we will see in the Spring may have actually taken root in the fall, however, and this includes various damaging fungal issues. One of the most common fungal issues we experience in Canada during early-Springtime is snow mold.

Identifying Snow Mold:

Snow mold usually starts to appear on lawns as the snow melts, and it will usually appear in areas of very deep snow cover or poor drainage where snow melt can collect. The fungus tends to appear as circles that range from a few inches across to a few feet across. If there are enough areas of infection that are close enough together though, it can start to look like one large infected area, and individual circles may not be indentifiable. The grass in infected areas is usually matted down and somewhat crusty, and a powdery, web-like growth can occur. There are two types of snow mold: grey and pink. If it is a grey snow mold infection, the powdery growth will be a greyish-white, and a pink snow mold infection will be a whiteish-pink. Grey snow mold generally just affects the blades of the grass, but pink snow mold is more severe and can kill the crowns and roots of the grass as well.

What Causes Snow Mold?

Like all fungal issues on lawns, the causes include five components: the presence of fungal spores, preferred grass species as hosts, turf health, moisture levels, and temperature. Snow mold prefers all the types of grasses we commonly have here in the GTA including common turf grasses like perennial rye grass, Kentucky blue grass, and fescues, as well as common weed grasses like tall fescue. Grass that lacks the proper nutrition is then more susceptible to an infection. All turf fungi like higher levels of moisture, and snow mold likes cooler temperatures between 0-15 degrees Celsius. Snow mold occurs then if there are fungal spores present in the late-Fall and early-Winter, and if heavy snowfalls cover the ground before the ground freezes completely. This then locks in moisture that is ideal for the spread of the fungal spores. So, areas of deeper snow or more shade where the snow takes longer to melt keeps the grass beneath cooler and wetter longer, and increases the risk of a snow mold infection. Other factors that can cause snow mold to appear in the Spring include leaving the grass too long at the end of the season and not raking up leaves before it snows. The long grass and leaves will help to prevent the ground from freezing, will reduce air circulation and light levels, and will hold in excess moisture.

How Can you Prevent Snow Mold?

We can prevent snow mold by taking the following steps in the Fall and Winter:

  • Keep the grass cut at 2.5 – 3.5 inches to avoid long grass being matted down by the snow
  • Rake up leaves before snow starts falling to make sure the ground is able to drain and freeze completely before snow begins falling
  • Rake out any thatch in the lawn before the snow falls to make sure moisture isn’t being held in the lawn, and to increase the amounts of air and sunlight
  • Try to make sure snow is spread out more evenly when shoveling walks and driveways rather than piling it higher along the sides.
  • Have a Fall fertilization done which is higher in phosphorus and potassium and will keep the nutrient balance more optimal throughout the Winter
How do we Treat for Snow Mold?

If snow mold does occur in the spring, then we need to consider the components that are involved in causing the infection: temperature, moisture, and nutrient balance. Gently raking the lawn to remove any thatch and dead grass will increase air flow and help with drainage to remove moisture. If you have a lot of tree cover creating shade, consider pruning the trees back to allow more sunlight and evaporation. As snow disappears and moisture levels drop, and as temperatures rise, the problem will start to dissipate naturally. A Spring fertilization will then help to restore the nutrient balance. If there is an area of damaged turf after the fungal infection disappears, then cut out and remove that turf to dispose of any remaining fungal spores, and put down new topsoil and seed to fill it in.


Remember, the best way to deal with snow mold is to take preventative actions in the Fall to avoid creating the conditions that can lead to a break out in the Spring. We can’t control the temperatures or the amount of snowfall we get – or even how early or late into the year it snows – but we can maintain proper lawn care practices by managing our cutting height and our watering habits. As mentioned, Fall fertilizations also help to strengthen the turf and balance nutrient levels throughout the Winter. If you do see an infected area, then don’t panic; gentle raking, Spring fertilization, and changes in temperature will all help to resolve the issue.