Fungus on indoor potting soil


Hello, I have a couple of potted plants (philodendron) indoors. There is a consistent film of white fungus all over the potting soil. I have tried scrapping it off, as well as repotting in different makes of potting mix, without any success in defeating the fungus. Some leaves have brown patches. I water, sparingly, once every 10 days. The indoor temperature is maintained at 68oF. Please let me know if there is anything I can do.


Thank you for contacting the Toronto Master Gardeners.

The white mold growing on the surface of your soil is probably a harmless saprophytic fungus, this could also be a sign that your plant is not getting enough sunlight or air circulation. The brown patches that you are seeing on your plant could be a sign of overwatering or improper drainage. Does your pot have drainage holes? Even the best watering technique won’t prevent soggy soil if the pot doesn’t drain freely.

We have received numerous questions concerning how to prevent this.The following is from one of earlier posts:

The ‘fuzzy white stuff’ on your soil is likely a fungus or mold.  A fungus or mold on potting soil is often the result of poor ventilation and overwatering.  When a room is cold as you mention your room is, the soil is very slow to dry out.  You do not mention how high or low the light level is in your home – if it is low, the plant soil will dry out slower, so you should water less frequently.

Let’s talk about what to do to eliminate the existing mold and then we’ll talk about prevention.

Remove the top layer of soil with the mold and add some fresh potting soil.  If the problem returns, it will be necessary to repot the plants into pots that have been well washed in a combination of bleach and water (1 part bleach to 10 parts water).  Remove all the old soil from the roots and wash off the roots.  Use fresh new potting soil to repot the plants.  It is not necessary to use diatomaceous earth.

Prevention is key.  Don’t overwater.  Poke a finger a good 2 cm (between your first & second knuckle) into the soil to determine if watering is necessary.  Don’t let the pot stand in water for more than 15-20 minutes – drain the excess water sitting in the saucer.  Ventilation can be increased by having a small fan lightly circulate the air around the plants.

When the ‘white stuff’ on top of the soil is crusty or more crystalline in appearance, it can be the result of salts in the actual water, or a salt residue from any plant fertilizer used.  In such cases, submerge the pot in a pail of clear water to flush out any excess salts.”

Good Luck with your Philodendron.