The Homeowners Column

The Homeowners Column

Fungi in mulch

Photo of Sandra Mason

Sandra Mason
State Master Gardener Coordinator

From frogs to fungi it's been a fertile year for anything of the aquatic persuasion. Constant moisture allows just about any surface to support life. Multitude of flat grey green lichen and bright green algae adorn tree branches. Neither causes problems for the tree. Branches are just good landing pads. We have had our share of wet weather fungal diseases such as root rots, leaf spots and fruit decay. However not all fungi in the landscape are bad.

Wood chip landscape mulch can develop its own assorted fungi. Majority of plants prefer organic mulches such as wood chips and compost instead of inorganic mulch such as rock. Organic mulch is naturally in the process of decomposing. That's just what stuff that "once was alive" does. The decomposition improves soil structure by adding organic matter.

A significant group of decomposers is fungi. After rains you may notice mushrooms or toadstools popping up overnight in mulch or in the lawn. Mushrooms are only part of the fungi story.

When a mushroom or toadstool appears we are seeing the fruiting or reproductive structure of the actual fungus. Just like an apple on a tree, the mushroom contains the spores or fungus "seeds" to produce more fungus. We do not see the majority of the underground fungus in these cases. They are either living off the mulch itself or on tree roots from a long dead tree.

Slime molds are not true fungus but can appear on the top of mulch. Slime molds are often bright yellow, but can also be white, gray, brown or red. They can vary from a few inches in diameter to a foot across. They are not decomposing the mulch, but are living off the bacteria and other critters in the mulch. They are (to use the technical terminology) just gross. Your first inclination is to look for a sick dog. Slime mold grossness originates from its resemblance to dog vomit; hence its other name of "dog vomit fungus". The bright colors of slime mold quickly turn brown then off- white and powdery until they are gone in a week or so.

One fungus goes beyond gross. The appropriately named artillery fungus can cause annoying spots on the sides of houses and cars. It first appears in mulch as tiny orange-brown to cream cups (one tenth of an inch in diameter) containing one very tiny black "egg". The "egg" is a mass of fungal spores. Mulched areas containing artillery fungus appear matted and lighter in color.

Artillery fungus orients itself toward light colored objects such as the side of a house or car and shoots the sticky black spore mass far and wide. With high winds the mass can reach a second story of a house. It's a pretty ingenious adaptation to "go forth and multiply". Not so good for us since the tar-looking spore masses are tough to remove.

Ok, what's the bottom line on this landscape fungus? There are certainly some fungi that cause plant disease, but it's not these guys. These are not harmful to landscape plants or people and pets unless they are eaten. Never eat any mushrooms unless you are 100% sure of their identity.

So what can you do? Wait and the mushrooms will dry up within a week or two. However you will probably continue to see the mushrooms periodically when conditions are right, often after a heavy rain. If they are growing off old tree roots, eventually the food source will be depleted. If you have small children or pets, you should rake or mow off the mushrooms as they appear. Aerating the mulch by raking will often help. With slime molds put the mat in a compost pile or a heavy stream of water will disperse it.

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