Gardeners use mulch to improve plant drainage, insulate roots from the weather and control weed problems. Mulch also protects plants from dangerous microorganisms that can cause plant diseases, but it can also foster the growth of stinkhorn fungi.
Stinkhorn fungi vary in color and size. The University of California Statewide Integrated Pest Management Program describes them as resembling a giant finger. Several varieties include the Clathrus columnatus or stinky squid stinkhorn, the Mutinus caninus or dog stinkhorn, and the Dictyophora duplicata or veiled stinkhorn. The upper end of the stinkhorn fungus is covered in a foul-smelling, slimy material that attracts spore-spreading insects.
In nature, stinkhorn fungi decompose organic matter in the soil and convert the nutrients into a form that plants can use, so they often grow on organic materials like mulch. Aside from attracting flies, stinkhorn fungi do not harm plants or lawns.
The Ohio State University Extension recommends purchasing mulch products that have low amounts of wood, choosing coarse wood products over finely-ground material and keeping the mulch depth to 2 inches or less. Soaking mulch after application also helps control fungal growth.
- Ohio State University Extension Fact Sheet: Control of Nuisance and Detrimental Molds (Fungi) in Mulches and Composts
- University of Wisconsin-La Crosse: Tom Volk's Fungus of the Month for July 1999
- University of California Statewide Integrated Pest Management Program: Mushrooms and Other Nuisance Fungi in Lawns
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