How to Stop Mold Growth on Houseplants

Lillian Downey

Mold growth on houseplants is a fairly common phenomenon, but that doesn't mean that you should ignore it. Some molds are relatively harmless for some plants, such as sooty mold that grows on the honeydew produced by some insects. Other molds, such as those that cause root rot, may cause your plants to die.

Reducing mold growth on your houseplants keeps them healthy and long-lasting, improves their appearance and reduces mold allergies in sensitive individuals.

  1. Make sure the mold really is mold. Sometimes salts and other dissolved minerals can leave a white residue on the top of your soil which looks like mold. From a distance, the two look similar, but upon closer inspection, you can see that the mold appears fuzzy, while the residue looks more crystallized.

  2. Identify the cause of your mold. Most cases of soil mold are due to overwatering. Mold requires a constantly moist environment to grow and thrive. A good rule of thumb for houseplants is to water when the top inch of soil has dried out. This means that the soil below this one inch is still moist, but has begun to dry out. This watering schedule will keep mold from having a consistently moist home. Another cause of mold is high humidity. If your home has excessively high humidity, try a dehumidifier, or add a fan to the area to circulate more air.

  3. Use vinegar to kill the mold. Mix your spray bottle with a tablespoon of distilled white vinegar with each gallon of water. Spritz this solution on the soil of your houseplant, covering the entire soil surface. Do not drench the area with the vinegar spray. You want to lightly mist the soil in about one to three passes, depending on the size of the pot. The vinegar changes the pH of the soil and kills the mold very quickly.

  4. Retreat the soil. If after three days, your mold isn't completely gone, mist the surface of the soil again. Soil mold is often killed with one treatment, but persistent soil mold may require two treatments. Also, retreat any time you see more mold reappearing.

  5. If after several treatments, your mold is not going away, consider using a spoon or small shovel to remove the top layer of soil which contains the mold. You can just scrape the soil off that has molded, or remove the top half inch and replace it with fresh mix. It is important to note that mold will continue to grow until the issues of overwatering and excessive humidity are solved.

  6. Tip

    If treating seedlings or other very delicate plants, try using a more diluted vinegar solution and make sure you are only very lightly misting the soil. You do not want to saturate the soil. The acid can damage a plant without an established root system. If you see mold on the plant itself, use the same methods to reduce its growth as you would for mold growth on the soil.