Mulch and Mushroom Growth

• Mulches and compost piles are composed almost entirely of decaying organic matter, so they are an ideal location for fungal growth. For the most part, mushroom growth on a mulch or compost pile is at worst a minor nuisance and will not threaten the health of your plant. Some species of fungi, however, can be problematic and can be agents of plant diseases that will infect your plants when the fungi-laden compost or mulch is applied to your plants.
  
  

Consequences

• Shotgun or artillery fungus (Sphaerobolus) can cause serious problems in plants and is commonly seen growing on mulch piles. When artillery fungus sporulates, it throws spores that are very hard to remove and can actually cause significant damage to plants and structures near it. Slime molds can also grow on mulch piles and cause serious, deleterious effects in plants. Other fungi may not be harmful to plants but produce toadstools --- mushrooms --- that are toxic to humans and animals, necessitating immediate removal. Verticillium dahliae and Rhizoctonia solani, two fungi that can cause a wide range of plant ailments, are also frequently seen growing in mulch and compost piles.
  
  

Approaches to Control

• Compost and mulch piles are often noticeably warm internally. This warmth is due to the presence of thermophiles, microorganisms that produce heat as they help decay the organic matter in the mulch and compost piles. Soaking these so-called "high temperature" mixtures with water after applying them to your garden can eliminate nuisance fungi by creating bacteria colonies that will compete with fungi for nutrients. Spade the mixture after it is applied to plants or heap thoroughly soaked mixtures to allow thermophiles to bring the internal temperature of the mixture back up to fungi-terminal temperatures above 100 degrees Fahrenheit.
  
  

Other Considerations

• If you would rather avoid nuisance fungi problems on your mulch and compost altogether, consider purchasing a compost or mulch mixture that is low in wood content. Another effective preventative measure is to carefully control the depth at which you place compost and mulch. Avoiding planting your compost or mulch deeper than 2 inches below soil level will not only eliminate nuisance fungi but will aid in the creation of beneficial bacteria and other microorganisms.