Mold in Houseplant Soil

Many people suffer from mold allergies.  An often overlooked problem area is mold in houseplant soil. It is a common source of mold that can be controlled by following these simple guidelines.

Causes of Moldy Soil

Mold likes high temperatures (mid 70°F), high humidity, darkness, and stagnant air.

How to Treat Mold in Houseplant Soil

When mold is discovered check to see if it is active (soft, fuzzy, smears easily) or dormant (powdery, easy to wipe). If it is active and it is in single plant replace the top inch of soil from the pot. If it is in the dormant stage, allow the soil to become quite dry. Then brush off the spores, working outdoors and (if possible) with a fan blowing the spores away. Some varieties of mold are toxic to humans, so please use great care. We suggest wearing rubber gloves and a dust mask to protect yourself. Take care to avoid the mycotoxins of toxic molds.

There are fungicides on the market that will kill the mold. Check with your local nursery or garden center for an appropriate one, and use only according to directions.

We prefer a more natural solution. Spray some white  or cider vinegar on the soil and let sit until dry. The acidity of the vinegar will kill mold and mildew. Also sprinkle some cinnamon over the soil. Cinnamon is a natural fungicide.

an example of mold in houseplant soilPrevention of Mold in Houseplant Soil

Be sure your soil is sterile. Whenever you bring home a new plant from the nursery there is a chance it has mold in the soil. To be certain the soil is mold-free repot the plant using sterile soil. Gently clear the roots of the nursery’s soil and repot in sterile soil. Usually potting soil purchased at a store comes sterilized (check the packaging). Some people go the added step of sterilizing in the oven for extra certainty.

Only water  when the soil is dry. Mold in houseplant soil occurs when the soil is constantly moist. Overwatering can be a problem or if your watering is done on a schedule. Always water by touch— the top of the soil should be dry before watering.

Increase exposure to sunlight. If possible allow the soil to be exposed to sunlight. Mold does not like light so adding more light helps control mold on indoor plants.

Use a fan.  Increasing air circulation around your plants is an effective precaution against mold in houseplant soil. Set an oscillating fan on low in times of high humidity.

Trim dead stems and leaves. Dead organic matter should be cleared away.

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