Slime Mould in Your Winter Lawn? What it is and How to deal It

Tammy Johnson
Jul 27
4 min read

Updated: Aug 10

Written and edited by Tammy 27th July 2025

If you're anything like me, even on the coldest, wettest wintery days I still grab a moment or two here and there to wander out on the lawn for some fresh air and a reality check before grabbing another chunk of wood for the fire. But have you ever come to a grinding halt, horrified by sight of some weird, gelatinous goo that looked like it came from another planet?

What Is Slime Mould?

Slime mould is one of nature’s weird little wonders, an odd-looking, harmless organism that’s often mistaken for something sinister. It’s not actually a fungus (or mould in the true sense) but a fungus-like 'stuff' that thrives in damp, organic-rich environments.

It doesn’t feed on your grass, just the decaying bits, like bacteria, leaf litter, and organic matter.

You might spot it as jelly-like blobs, powdery smears, or even as foamy splashes that look like someone spilled a bucket of paint across your lawn. Spooky? A bit. Dangerous? Not at all.

These little blobs usually pop up after rain, heavy dew, or long stints of overcast, cloudy, damp weather, especially in shady or poorly drained corners of the yard.

Is Slime Mould Harmful to Lawns?

The short answer? No. It might look a little, alarming and unsightly, but slime mould won't harm your grass. At worst, a thick patch of it might momentarily block some sunlight if it blankets the grass thick enough, but once things dry out, it’ll usually disappear all on its own.

So if you can live with it for a little while, do! It’s part of a living, breathing ecosystem under your feet.

How to Get Rid of Slime Mould (If You’re Not a Fan)

Ok I get it. It doesn't tick the box for 'aesthetics', quite likely a slip hazard for grandma on her way to the washing line, and definitely not what you'd like the curious grandies playing in or adding to their mud pies. So, if waiting for it to leave on its own isn't an option, here's a few safe and simple things you could try:

Rake it lightly or brush it off with a broom, nothing too aggressive, just enough to break it up and get the air flowing. It'll dry out much faster with a bit of encouragement.
Ease up on the watering, especially if you've had decent rainfall lately (like we have!). Your soil’s likely hanging onto plenty of moisture already. If you’ve got automatic sprinklers running, it might be time to hit pause for a bit, no need to overdo it when nature’s already doing the job for you.
Keep the grass mown to reduce thatch buildup and let the air and sunlight in to ground level. Thatch acts like a sponge and creates the perfect hideout for moisture-loving organisms like slime mould.
Improve air circulation and drainage, consider aerating compacted areas or using a soil wetter in hydrophobic spots to help water soak in more evenly.
Encourage beneficial soil life, adding compost or worm castings supports microbes that naturally compete with unwanted fungi and slime.
Topdress low, soggy areas with a mix of sand and compost to even out dips and improve surface drainage.
Let the chooks help A gentle scratch around (supervised of course) can disturb the mould, dry the area out, and even reduce pests while they’re at it. Let them out for a scratch around on the lawn occasionally, they’ll aerate, de-thatch and snack on bugs all in one go.

For the “Spray-and-Walk-Away” Crowd

If the frustration gets the better of you, here are a couple of gentle, garden-safe options that still feel like you're doing something, without harming your lawn or your soil:

Diluted vinegar spray: Mix 1 part white vinegar with 4 parts water and lightly spray the slime mould to help dry it out faster. Just go easy, vinegar in strong doses can affect surrounding grass and soil microbes if overused.
Lemon juice and water mix: Mild, citrusy, and smells better than vinegar! Same idea, use it as a light mist, not a dousing.
Sprinkle a little garden lime: Not to kill it, but to help raise the pH slightly and discourage future growth in really acidic, damp spots. Just a light dusting, too much lime can throw your soil balance out of whack.
Bicarb spray (baking soda): 1 tablespoon of bicarb in a litre of water can help dry and discourage some fungal-like growths. It’s gentle and safe, just don’t soak the area.

Important: These remedies are more about satisfying that “doing something” itch, they’re not miracle cures. But they won’t harm your soil like harsh fungicides would either. Always spot test first and apply sparingly.

Slime mould might look like something straight out of a sci-fi, but really, in all honesty it's just nature doing its thing. In fact, it’s a quirky little sign that your soil is full of organic matter and teeming with microscopic life.

So, unless it’s really bothering you, take a deep breath and move on to the next check box on the 'garden to do list'. It’ll be gone before you know it and your lawn will be no worse for wear.

Keep warm and enjoy this beautiful winter rains.

Happy Gardening 😘🪴