How to Treat Mildew on Plants

To treat mildew on plants, it is important to select a method that will not harm the plant. Using the below instructions can help you with mildew problems on your indoor and outdoor plants.

Step 1: Safety

Oxygen bleach is superior to chlorine bleach because it is non-toxic and will not harm plants or animals. It is safe to use on anything water washable. While oxygen bleach does not create the hazardous fumes chlorine bleach does, it is wise to take precautions. Keep the work area ventilated by turning on an overhead fan or air conditioner. You can also open a window. Use caution when handling oxygen bleach, avoiding contact with the eyes or skin. Wearing gloves or safety goggles can reduce the likelihood of injury. Never mix any bleach with ammonia, as this can create a dangerous gas. 

Step 2: Mix the Bleach

To mix the oxygen bleach, check to see if your spray bottle has a measurement guide on the side. If not, most spray bottles are either 24 or 32 fluid ounces. You can use a measuring cup to determine the amount the spray bottle holds. Using the oxygen bleach, mix 6 to 8 ounces per gallon of hot water or 2 ounces per quart. This equals approximately a cup's worth of bleach per gallon.  Make sure you use hot water with the bleach. This activates the chemical, sodium percarbonate, in the bleach.

Step 3: Apply the Bleach Mixture

Spray the bleach mixture on the plant anywhere mildew is growing. This includes the leaves, branches, and trunk. When finished, allow the mixture to sit for about fifteen minutes. Avoiding spraying the plant in direct sunlight. You do not want the bleach solution to dry on the plant.

Step 4: Rinse

Use a water hose to rinse the plant thoroughly. On branches and the trunk, you can use stronger water pressure to blast loose mildew off. For small indoor plants, you can use a sink sprayer to clean them.

Step 4: Repeat as Necessary

When the plant is dry, inspect it for any remaining mildew. If mildew is still present, reapply the oxygen bleach and re-rinse.

Step 5: Prevention

Remember that mildew thrives in moist, warm, and shady environments. Your plant provides the organic material for mildew to thrive off of. By reducing the relative humidity, you can prevent mildew from forming on indoor plants. Turn on the air conditioner to reduce the temperature and use a dehumidifier to lower moisture levels. Ultraviolet light is not likely to kill established mildew, but it will help to prevent new mildew from forming. Placing your indoor plants in sunlight will deter future mildew growth. Also avoid overwatering your indoor plants. Watering on a set schedule can sometimes lead to too much water or moisture in the plant, thereby causing mildew to form. Allow for the top 1 to 2 inches of plant soil to dry in between waterings.