Question:
One of my houseplants has several small, yellow mushrooms on the surface of the potting soil. Will the mushrooms harm the plant?Answer:
The small, yellow mushroom is probably Leucocoprinus birnbaumii. The fungus is sometimes referred to as yellow houseplant mushroom, yellow parasol, or flower pot parasol. This species can be found outside in summer, but is most commonly found year-round with potted plants or in greenhouses. The small, lemon yellow mushrooms are about 1 to 3 inches tall with 1 to 2 inch oval or bell-shaped caps. They may appear singly or in clusters.
A mushroom is the reproductive structure of a fungus that spends the rest of its life cycle as a thread-like body in the soil or debris, not usually visible. That thread-like body, called a mycelium, could have been introduced to the pot in the potting mix. Alternately, a spore of the fungus (similar to a seed) may have floated through the air and landed in the pot, starting the fungal colony.
The Leucocoprinus birnbaumii fungus breaks down dead organic matter in the potting soil. It does not harm living plants and mushrooms do not need to be removed for the plant's sake. However, the mushrooms are regarded as poisonous to people and animals. If pets or small children reside in the home, it would be wise to remove the mushrooms as they appear. Fungicide treatments are generally not effective against mushrooms.
To learn more about mushrooms see Mushroom Questions Answered