Understanding the role of mushrooms in the environment can often ease the concern homeowners have when they observe mushrooms growing in their lawn and mulch and want to know what action can be taken.

The mushrooms we commonly see in our landscape are fungi. Instead of the thread-like structures often associated with fungi, we are seeing the fruiting bodies.

Mushrooms come in all shades of color, except green. In plants, green signifies the presence of chlorophyll, necessary for photosynthesis which allows the plant to produce its own food and energy. Since mushrooms don’t have chlorophyll to capture the sun and produce food, they have to obtain energy in a different manner.

Everything in the landscape rots over time. Mushrooms aid in this destructive process and utilize decaying items to obtain their energy. Nutrients are also released in this activity and become available to nearby plant roots.

While there are some fungi that will attack living plants to obtain energy (parasites, and these are the ones to worry about), the mushrooms we see in the landscape are causing no harm to surrounding plants. That being said, many homeowners see mushrooms in the yard or mulch as an aesthetic nuisance (although some might be harmful if eaten).

For mushrooms growing in the lawn, simply mow over them. These will eventually disappear when drier weather remains in place or when the organic matter it is feeding on is completely decomposed. Fungi in the mulch can be eliminated by simply raking over the mulch.

Landscape mulches are used to protect soil, conserve moisture, moderate soil temperature, and limit weed growth, as well as beautify and unify landscape plantings. Most mulches are mixtures of shredded wood and bark residues from lumber and paper mills, arboricultural and land-clearing operations, and wooden pallet disposal or recycling facilities.

As does other organic matter, wood and bark decompose over time. The primary organisms involved with their decomposition are bacteria and fungi, which derive their energy for growth from the carbon-based compounds found in wood and bark. The fungi involved in the decomposition of landscape mulches are natural components of the mulch environment.

Some fungi, such as the artillery fungus, are “recyclers” and break down woody tissue directly. Other fungi, such as slime molds, consume bacteria and other organisms living in the mulch. These fungi are not harmful to landscape plants, and no known health hazards are associated with them unless they are eaten.

Artillery fungus resembles a tiny, cream or orange-brown cup with one black egg. The cup is approximately one-tenth inch in diameter. Areas of mulch with artillery fungi may appear matted and lighter in color than the surrounding mulch. They can be a problem.

The fruiting body of this fungus orients itself toward bright surfaces, such as light-colored houses or parked cars. The artillery fungus “shoots” its black, sticky spore mass, which can be windblown, as high as the second story of a house. The spore mass sticks to the side of a building or automobile, resembling a small speck of tar.

Once in place, the spore mass is very difficult to remove without damaging the surface to which it is attached. If removed, it can leave a stain. A few of these spots are barely noticeable, but as they accumulate, they may become very unsightly on houses or cars.

Bird’s nest fungi resemble tiny, gray to brown bird’s nests or splash cups with eggs. The nest is up to one-quarter inch in diameter. These fungi may grow in large areas of mulch, but they are not a problem.

The “eggs” are masses of spores that splash out of the nest when hit by a raindrop. These spores occasionally stick to surfaces, as do the spores of the artillery fungus, but they are easily removed and do not leave a stain. These naturally-occurring fungi decompose organic matter and do not need to be removed.

“Growing Green” is contributed by Lehigh County Extension Office Staff and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-746-1970.