What Is The White Mold In My Mulch—And Is It Harmful?

When you open a new bag of wood mulch, you may notice thin white threads or a powdery white coating growing in it. The same thin white threads can appear in wet mulch in your garden, especially when you disturb the top layer to plant something new. Sometimes you’ll even see a large, whitish blob growing on top of your mulch after a warm rain. Alarmingly, the blob may morph and move around from day to day.

As terrifying as that sounds, the white mold in your mulch isn’t going to harm your plants. You can leave the white mold on your mulch alone—here’s why.

What Is The White Mold In My Mulch?

Fungus grows in mulch just the same as it does in decomposing wood on the forest floor. This is no cause for concern. The white threads are the underground growth of fungi, otherwise known as mycelium. When mushrooms appear aboveground, these are the fruiting bodies of fungi.

As for the creepy blob on your mulch, this is another primitive organism called a slime mold. Some refer to it as “dog vomit fungus,” which gives you a good idea of what it looks like. The slime mold may be bright yellow-orange and oozing when it first appears. Then it dries out, fading to white or brown and producing spores.2 Eventually, the slime mold will disappear on its own.

Should I Remove The Mold?

The mold on your mulch serves a beneficial role by breaking down dead plants and wood and returning nutrients to the soil. These organisms aren’t parasitic and won’t harm your plants (though slime mold will sometimes surround garden plants). If you leave the mold alone, it will dry out and fade from the surface.

If you can’t bear the sight of moldy mulch in your garden, turn it over with a shovel or rake so you no longer see it. This also helps the mulch dry out more quickly. Plants can suffer from root rot and other diseases when they spend too much time in soggy mulch and soil.

Tips To Prevent Mulch From Turning Moldy

Here are a few tips to keep your mulch from turning moldy:

• Slit open new bags of mulch and lay them in a sunny spot for a few days to dry out before spreading.
• Don’t water your garden with a sprinkler, which will wet down the mulch and promote mold. Instead, water individual plants with a hose or watering can.
• Water in the mornings so that the mulch has all day to dry out.
• Fix drainage problems in wet areas of your yard.
• Use a rake to thin out layers of mulch that are more than 2 or 3 inches deep.