Mushrooms are the above-ground fruiting bodies-the “flowers”-of a fungus that lives on decaying organic matter in the soil. The rest of the fungus is a mass of fibers in your soil. You can see them by lifting some forest duff; the network of fibers on the bottom is a fungus mycelium—the body of the fungus. Mushrooms thrive in damp areas, frequently sprouting up in a lawn after wet weather.
Like flowers, mushrooms “bloom” when conditions are right. Depending on the species, it might have a bloom that lasts for a couple of weeks in the spring or fall, or bloom sporadically over the whole summer. Mushrooms may appear in the lawn individually or in clumps.
Fungi that make mushrooms are not lawn diseases; they do not harm living grass, but instead decompose organic matter in the soil, releasing nutrients for the use of the grass. A few species of lawn mushrooms are distinctive:
Some types form fairy rings, rings of mushrooms that may be accompanied by brighter green grass or dead grass. These rings can form in a lawn without mushrooms being present, also. The fungi that cause fairy rings are decomposing a thatch layer in the soil. As they decompose the thatch, they release nutrients that make the lawn greener and more healthy in that spot, forming a dark green ring. The mycelium begins in one spot and grows outward, forming a ring that may grow for years. Sometimes the mycelium is so dense that it forms a waxy, waterproof layer in the soil that prevents water from getting to the grass. This forms a ring of dead or weak grass.
Another fungus is a tree disease called Armillaria root rot. After killing a tree, it lives on the stump and buried roots for years, decomposing them. It forms tightly-packed clusters of yellow mushrooms in the spring, called “honey mushrooms”.
Puffballs are golf ball-sized mushrooms without stems or cap. Giant puffballs are a type of puffball the size of a football.
So what can you do about them?
- You can ignore them and think of them as cute decorations for your lawn.
- You can break them off with a rake or mow them along with the rest of the lawn. But this won’t get rid of the underlying fungus any more than picking roses will make a rose bush go away.
- If the mushrooms are living on buried scrap lumber or a buried tree stump, you can dig up the wood to remove the source of food.
- You can wait for them to finish their dinner. Once the stump or wood or thatch is decomposed, they will disappear. This might take a few years, however.
- You can control the damage from fairy rings by aerating weak regions of the ring, then watering well. Fertilize the entire lawn to mask a green ring. For a longer-term solution, dethatch the lawn to remove the food source.
- You can hire a lawn care company to kill fairy rings. They use a chemical called Flutolanil that isn’t available to home gardeners. This is only effective on fairy ring fungi, however, not fungi living on buried stumps or wood.
- There is no chemical control available to home gardeners for their control.