Indoor – White Fuzz on Soil*


Hello. I have a few small indoor plants that have white fuzzy stuff on the top of the soil. The room is cold and dry ..could it still be fungus? I have never seen any gnats or any other insects. I do not water too much, I don’t think. Would diatomaceous earth help? If not, what can I sprinkle on top?
Thank you.


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.