When gardening organically, one has to think differently than conventional gardening. Mushrooms are naturally occurring in all soils, but can be more prevalent in organic soils.
Mushroom blooms usually occur in decaying matter when the soil is exceptionally damp, either through over watering or poor drainage. We tend to notice them more as we transition from the warmer summer months into cooler fall or winter months because our watering habits tend to be more frequent in the summer due to the heat. We have to remember to “back off” the watering as the air cools and soils take longer to dry out. Because mushroom mycelia (roots) grow on decaying organic material, plants are safe from the mushrooms and it is not uncommon to have mushroom blooms happen with rich organic material. Reduce the amount of watering to the area and ensure your soil drains properly. The mushrooms will disappear in a few days.