How to Kill Powdery Mildew in Mulch

Lay down a tarp in a location near the mulch but away from any plants that you are growing.

Move the mildew-infested mulch over to the tarp using a shovel. This will help prevent the soil from being affected by the anti-mildew agents you'll be using.

Spray the mulch with a bleach-based mildew killer. Bleach is toxic to mildew but it can damage other plants if it soaks into the soil, which the tarp will prevent. Turn the mulch over with the shovel and respray to ensure the spray contacts all the mildew. Allow the mulch to sit for about 10 minutes.

Rinse the mulch thoroughly in water with a garden hose. Turn it over with the shovel and re-rinse several times to make sure you wash off all the cleaner. Allow the mulch to dry.

Move the mulch back to its original location once it is completely dry.