Extension Educator, Horticulture
There is a fungus amongus. After a rain you may notice a flush of mushrooms that appears overnight in the wood mulch. Now before you get concerned that you have been invaded by the body snatchers, realize most of these are growing on decomposing plant material. The organic mulch, such as the wood chips that we use, is naturally in the process of decomposing. That's just what stuff that "once was alive" does. Like a teenager with a cell phone, they just go together.
Now let's drop down to the life of a fungus. When we see a mushroom or toadstool 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 in the case of slime molds are living off the bacteria and other critters in the mulch. They may also be growing off of old tree roots. The tree could have been cut down years ago, but the roots are still decomposing. Fungus can live in the soil for years and only produce mushrooms when the environmental conditions are right.
You may see what we typically call mushrooms. The fruiting structure can also look quite weird. Ones that you may see are stinkhorns, puffballs or slime molds. With stinkhorns their reproductive structure looks like a giant slimy finger or a male reproductive structure. The spores are on top in a goo that may stink and often attracts flies. Luckily attributes not shared in the human counterpart.
Puff balls look like the name implies - a round ball. As they ripen, the ball gets a hole in the top and when the structure is disturbed it sends out a puff of spores. These are fun to play with.
Slime molds are (to use the technical terminology) just icky. They are not true fungus but will often appear on the top of mulch. It looks like your dog got sick, hence its other name "dog vomit fungus". Some may be bright yellow, but can also be white, gray, brown or red. They generally quickly turn brown then kind of white and powdery until they are gone in a week.
Ok, what's the bottom line on this landscape fungus? There are certainly some fungus 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. Some mushrooms are edible and some poisonous. Even guidebooks do not give you the necessary details to safely eat mushrooms. Question is "Do you feel lucky kid?" If you want to eat mushrooms, go out hunting with an old mushroom hunter. If they have made it past fifty with their liver intact, then they have probably been doing it right.
So what can you do? Wait and the mushrooms will dry up. However you will probably continue to see the mushrooms periodically when conditions are right often after a heavy rain. 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. Just aerating the mulch will often help. With slime molds a heavy stream of water will disperse the mat. When you cut down a tree, try to remove as much of the stump and roots as possible. These decomposing fungus may be a nuisance but are important in the nutrient cycle as they make nutrients more available to plants. Plus they are a great conversation piece.
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