Ask the Master Gardener: Mushrooms can be both friend, foe

By: Pauline Kuklis Placer County Master Gardener
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Question: Mushrooms have been appearing in a shaded area of my garden. I am receiving conflicting advice from friends about what I should do with them. Are mushrooms in the garden good or bad? Answer: Well, that depends! Mushrooms are the fruiting bodies of various types of fungi. Most mushrooms are good for the yard and garden, as they help to decompose organic matter and return nutrients to the soil. It is quite common for mushrooms to pop up during periods of moist conditions resulting from either natural rainfall or excessive irrigation. This is especially true if your soil is full of good, organic material. A large group of beneficial fungi, known as mycorrhizal fungi, connect themselves to the roots of trees and shrubs. They help the plants absorb nutrients and water from the soil. The plants return the favor by supplying carbohydrates to the fungi. Without this symbiotic relationship, many trees would have difficulty surviving. Mycorrhizal fungi reproduce annually and their fruiting bodies (mushrooms) may appear in your lawn or garden during moist, cool times of the year. Some mushrooms, however, are extremely toxic. There are well over 50,000 species of fungi, and only about 250 are considered delicious edibles. Another 250 are quite poisonous — even deadly when eaten, so be sure to remove them from your garden if small children or pets are likely to ingest them. This can be done by simply raking and disposing of the mushrooms before they have a chance to develop reproductive spores. Note that removing mushrooms does not kill the underground mycelia from which they grow. Since most spores can be wind-blown over long distances, they can easily come into your lawn from neighboring areas. Dethatching lawns can also reduce the growth of mushrooms in lawns since it removes their source of food. Have gardening questions? Call the Master Gardener hotline at (530) 889-7388.