Landscape mulch usually consists of hardwood shreds or bark chips, providing cover to hold moisture and add a finished look. Wood in mulch also provides a food source for fungi that are natural decomposers, breaking down plant material and utilizing organic matter. Without fungi, dead leaves, twigs and branches would clutter forests and landscapes. We see fungal fruiting bodies after growth of threadlike mycelium in soil and mulch. The most recognizable of these spore producing bodies are mushrooms, but sometimes they produce other structures, such as slime molds, stink horns, bird's nest fungi, and artillery fungus.
Most of these are harmless, providing decay of excess organic matter. Addition of fresh mulch yearly and raking to break up surface growth can prevent these fungi from sporulating. Artillery fungus can leave unsightly spots from spores deposited on siding, walls and cars. Use of pine bark or nuggets rather than hardwood reduces growth of artillery fungus.
NFG 4/2019