There are many fungi that may live in the potting soil where your houseplants are growing. Most are not harmful to the plant itself, but they are unattractive and may be poisonous to pets or children if consumed. They range from simple mold or mildew to small mushrooms growing next to tour plants. Controlling fungus in potting soil begins before you even place it in the container. Once it is in the container and infected it is more difficult to eradicate, though it can still be controlled.
Purchase only sterilized potting soil or sterilize the soil yourself before using, to kill any fungus spores. Place soil in a roasting pan and cover with foil. Bake in a 200 degree oven for 30 minutes, then let it cool before using.
Avoid over-watering houseplants and empty the drip tray under them whenever there is standing water. Too much moisture is the cause of most fungus problems.
Scoop out the fungus from the potting soil as it appears and dispose of the soil. Scoop it out with a small spoon, making sure to remove the soil under the fungus or the entire stalk in the case of mushrooms.
Treat mold and mildew with a fungicide formulated for houseplant potting soil. Follow package instructions for application.
Re-pot the plant. Remove the plant from its pot and set aside. Rinse the pot out in a solution of one part bleach to 10 parts water, to kill any fungus spores on its surface. Shake off as much of the existing potting soil from the plant's roots and replant in fresh, sterilized soil.