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Martha Maletta, Home Horticultural Consultant
Dated - September 21, 2004
Plentiful rains mean plenty of fungi popping out in all sorts of places. During a recent mountain hike I must have seen 15 to 20 different sorts of mushrooms along a few feet of trail. Mushroom identification I leave to the mycology experts, but the variety of shapes, sizes and colors is fascinating.
The fruiting bodies of fungi, which we commonly call mushrooms, toadstools, and puffballs, appear where the fungus that produces them as part of its lifecycle grows. Fungi cannot feed themselves, as plants do, but need an outside source of nutrients. Depending on species, this may be dead or, in the case of fungal disease, living plant tissue. Around the home, decay fungi may grow in an old tree stump, firewood, some buried construction wood, roots of a long-gone tree, compost, landscape mulch and really anywhere there is a suitable substrate.
Most of the mushrooms that grow in the landscape on dead plant material are not a problem. The most significant concern is their potential attractiveness to young children. Since some could be poisonous, removing or physically destroying them would be the judicious course. If appearance is aesthetically objectionable, removal or destruction is the option. There is no treatment available that will prevent mushrooms other than removing the food source (substrate), which may or may not be possible.
The one fungus that may be a problem around the home is artillery fungus (Sphaerobolus stellatus). The problem relates to this species spore dispersal mechanism: the forcible ejection of sticky, dark spore bodies, which are very noticeable on light-colored surfaces – homes, cars, porch furniture – and have been commonly blamed on insects, wayward road tarring, aerial debris and assorted other causes.
The fruiting body of this very common fungus - the stage that does the "throwing"- is a tiny (less than 1/8 inch diameter) cream-color to orange-brown sphere that grows on decaying organic matter including rotted wood and the bark and wood mulches used in landscape plantings around homes. When temperature and light conditions are right, the mature fruiting body opens into a tiny cup with the spore mass (peridiole) "loaded" and ready to go. About five hours later the cup everts and the peridiole is thrown into the air, reportedly as far as 20 feet. Because it has a sticky coating, it will adhere tightly to any surface it contacts.
This fungus itself is not hazardous. The spore masses pose no threat to plants they happen to land on and they are no hazard to structures, etc. But, they can be very unsightly on buildings and other surfaces, very difficult to remove and often leave behind a stain when scraped off. To date, I have not come across any recommendations for easy, effective removal.
The popularity of wood and bark mulches in the landscape probably accounts for increased encounters with artillery fungus and other fungi in recent years. With proper handling and use, the benefits of mulch should outweigh problems. A recent article from the University of Kentucky, reporting on research at Ohio State University, gives several suggestions for reducing fungi in mulch. Purchase composted mulch products that are high in bark rather than wood content. Avoid finely ground mulches unless they have been composted. Use coarse mulches. Do not apply any mulch deeper than 2 inches. Soak mulch with water immediately after application to encourage bacterial colonization that will compete with fungi.
The recommendations for reducing mushrooms in mulch will also reduce invasion by fungi that eventually turn an excessive mulch layer into a water repelling mass, which can cause a drought situation. There are many other reasons to avoid over-mulching trees and shrubs. For more information on proper mulching consult the RCE Fact Sheet “Problems With Over-Mulching Trees and Shrubs”, which is available on-line at or by calling the Rutgers Master Gardener Helpline at 908-788-1735, M, T, Th, 9 a.m. to noon and Thurs 12:30 to 3:30 p.m.
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