Q. What can I do about mushrooms in my lawn?
Most mushrooms that appear in lawns are what we call “nuisance mushrooms” because they are relatively benign and are not a symptom of a serious fungal problem.
Fungi are naturally present in the soil, and healthy soils contain an abundance of different fungi species. Mushrooms, the visible parts of soil fungi, are known as fruiting bodies and produce the spores that enable fungi to spread and reproduce. Mushrooms tend to appear after heavy rainfall or when soil remains wet for an extended period. If there are old wood scraps from construction debris buried in the lawn, dead tree roots, or a heavy buildup of thatch, mushrooms may appear as the fungi are hard at work breaking down the organic matter.
If you are concerned about children or pets encountering these mushrooms, simply pick them and discard. The fungi can continue to break down whatever is lurking under the turf. Most mushrooms are not poisonous – but since the poisonous ones are really dangerous, you should always use caution when handling them.
Sometimes a dark green, rounded arc of grass appears in the lawn (with or without mushrooms). This is called a “fairy ring” and can range in size from 1 to 12 feet in diameter. Several species of fungi can cause this usually harmless phenomenon. If there is only a dark green ring or arc (with no other damage to nearby turfgrass), simply apply a nitrogen-rich fertilizer to the entire lawn at the rate of 1 pound of nitrogen per 1000 square feet. The dark green is due to increased soil fertility from the byproducts of fungal decomposition. Applying nitrogen will even out the grass color so the rings won’t be as visible.
If there is dead or sickly-looking grass near the fairy ring or mushrooms, the fungus may have grown too dense. Mycelium are thread-like structures that compose the main body of the fungal organism. When these structures become overgrown, they can interfere with grass roots’ ability to take up water and nutrients. Dig out a soil core sample – the mycelium should be visible to the unaided eye. If this is the case but the thread mat is not too thick (less than 2 or 3 inches), aeration can be helpful. If the mat is very dense or thick, it may have to be dug out by hand and removed. Discard the removed material so as not to spread the fungus further. Fill in the dug out areas with fresh soil and, if necessary, re-seed.
If this is a recurring problem, you may want to inspect your irrigation system for leaks or evaluate your property’s drainage and make any needed repairs or corrections.
Los Angeles County
mglosangeleshelpline@ucdavis.edu; 626-586-1988; http://celosangeles.ucanr.edu/UC_Master_Gardener_Program/
Orange County
ucceocmghotline@ucanr.edu; http://mgorange.ucanr.edu/
Riverside County
anrmgriverside@ucanr.edu; 951-955-0170; https://ucanr.edu/sites/RiversideMG/
San Bernardino County
mgsanbern@ucanr.edu; 909-387-2182; http://mgsb.ucanr.edu