Will Mold in Leaves and Wood Chips Harm Your Soil?

“Will the mold from decomposing leaves and wood chip piles harm your soil?” Question from Sylvia of Belle Plaine, Minnesota

Answer: The molds involved in the decomposition of dead plant material are generally not disease causing to live plants, so they should not harm your garden plants. They are distinct from disease-causing fungi.

The soil is filled with fungi of all kinds at all times, some can cause plant disease and others do not. Those fungi that are disease-causing and remain in the soil are brought on by live plants that have contracted fungal diseases and passed them into the soil. These fungal diseases are generally crop specific. Crop rotation on a three-year cycle is the best way to ensure that your different crops are protected from soil-borne fungal diseases. For example, if your tomatoes get fungal late blight, plant beans where your tomatoes grew the previous year followed by squash the next year. By the third year, the late blight should no longer be a problem where you originally planted your tomatoes, and you can plant them in that spot again.

With that said, excess mold spores in the air are not good for human health. Excess moisture encourages mold growth, so to reduce mold in your leaf and wood chip piles, keep them turned regularly to increase air flow. If you plan to use them as garden covers, the mold will dry out once the leaf mulch and wood chips are spread out. Then they won’t be a problem.

Happy gardening!

Jessie Keith

Black Gold Horticulturist


Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.

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