Snow Mold: How to Prevent It This Fall (and Fix It in Spring)

In this guide

1. What snow mold is
2. Why lawns get it
3. Fall prevention checklist
4. Do you need a fungicide?
5. Fixing snow mold in spring
6. Common mistakes to avoid
7. The bottom line

Every spring, as the last snowbanks shrink, a lot of Northeast homeowners find circular, matted, crusty patches in the lawn, sometimes with a gray or pinkish fuzz on them. That's snow mold. It looks alarming, but it's usually cosmetic, and most of it can be prevented with a few simple habits in late fall.

What snow mold is

Snow mold is a group of fungal diseases that grow in cold, wet conditions, often under a long-lasting snow cover. Two kinds cause most of the trouble in the Northeast:

Both show up most often where snow sits longest: the north side of the house, along driveways where plowed snow gets piled, and in low spots.

Why lawns get it

Snow mold needs a cool, moist environment with grass that's matted down and slow to dry. The biggest risk factors are things you can control in the fall:

• Long grass going into winter. Tall, floppy blades fold over under snow and create a damp, insulated mat.
• Leaves left on the lawn. A layer of wet leaves under snow is ideal for fungal growth.
• Snow piled in the same spot every year. Big piles melt last and keep the turf covered for weeks longer than the rest of the lawn.
• Heavy, late, slow-release nitrogen. Lush, soft growth heading into winter is more susceptible. A normal late-fall feeding is fine; excess isn't.
• Thick thatch. It holds moisture against the grass crowns.

Fall prevention checklist

1. Keep mowing until the grass stops growing

Don't stop mowing in mid-October just because the season feels over. Keep cutting at your normal height as long as the grass is still growing, which in much of the region means into November.

2. Lower the deck for the last cut or two

For the final mowing or two of the year, lower the mower to about 2 to 2.5 inches. Shorter grass is less likely to mat under snow. Don't scalp it, and lower gradually rather than in one dramatic cut. Our mowing height guide covers the full-year heights.

3. Get the leaves off

Mulch-mow light leaf cover into the lawn, and rake or blow away anything heavier before the first lasting snow. See mulch-mow or rake? for how much your lawn can handle.

4. Feed sensibly

A late-fall application of quick-release nitrogen, as described in our fertilizer schedule, supports root growth without pushing a lot of soft top growth. Avoid heavy doses of slow-release nitrogen late in the season. And check your state's cutoff date first: New Jersey, for example, bans homeowner fertilizer applications from November 15 to March 1.

5. Plan where the snow goes

If you shovel or snowblow, spread the snow around instead of building one giant pile on the same patch of lawn every storm. If you have a plow service, ask them to push snow onto a gravel area, a garden bed or a different spot from last year.

6. Deal with thatch and drainage over time

If you have more than about half an inch of thatch or water that sits in low spots, core aeration next fall and gradual topdressing of low areas will help.

Do you need a fungicide?

For most home lawns, no. Preventive fungicides are used on golf courses, where every square foot matters, but on a home lawn the damage is usually cosmetic and recovers by late spring. The cultural steps above prevent the large majority of problems. If you have a recurring, severe pink snow mold problem in the same area every year, talk to your local extension office before spending money on a product.

Fixing snow mold in spring

If you do find patches after the snow melts:

1. Wait for the lawn to dry a bit. Walking on soggy turf compacts the soil.
2. Lightly rake the matted areas. A leaf rake or a gentle pass with a flexible rake breaks up the crust and lets air and sun dry the grass. This alone often makes a dramatic difference within a week or two.
3. Spread out any remaining snow piles so the grass underneath gets light sooner.
4. Give it a few weeks. Most gray snow mold patches green up on their own as the grass starts growing.
5. Reseed what doesn't recover. If a patch is still dead by mid to late spring, loosen the soil and reseed it, or plan to overseed in late summer, which is the better seeding window in the Northeast. See the fall seeding guide.

Hold off on fertilizing until the lawn is actively growing in spring. Pushing growth on stressed turf in March doesn't speed recovery.

Common mistakes to avoid

• Stopping mowing too early. Long grass under snow is the number one setup for snow mold.
• Scalping the lawn in one cut. Lower the height gradually over the last couple of mowings.
• Leaving a mat of wet leaves under the first snow.
• Piling all the snow in one spot on the lawn every storm.
• Panicking in spring and applying fungicide or fertilizer to patches that would have recovered on their own with a light raking.

The bottom line

Snow mold is mostly a fall problem with a spring symptom. Keep mowing, finish short, clear the leaves and spread the snow around, and you'll see far less of it. If some patches show up anyway, a light raking and a little patience usually take care of it.

For everything else to do before winter, see the winterizing guide and this month's checklist.

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