How to Get Rid of Mildew on Cedar

Cedar is often used for outdoor construction because it generally holds up well to the elements.

However, cedar is still susceptible to a range of weather-related wear and tear, especially mildew. Getting rid of mildew on cedar takes a little elbow grease, but it's not entirely impossible. Mildew that has set in to cedar will continue to grow unless you are aggressive in killing it. A simple household solution can fix your mildew problem and restore your cedar's color and durability.

Purchase a spray canister at a hardware store. Look for the same type of sprayer marketed for use with insecticides.

Mix in the spray canister three quarts of water, one quart of bleach and one-quarter cup of liquid dishwasher detergent that is ammonia free. The bleach will kill the mildew and the detergent will help to remove any dirt and mildew remnants.

Spray the cedar thoroughly. Let the solution sit for10 to 15 minutes to allow time for the bleach to kill all the mildew.

Rinse with a hose or pressure washer. Repeat the treatment if necessary to ensure that all the mildew is removed. Allow the wood to dry completely for one or two days.

Treat the cedar with a water-repellent stain or preservative that contains a mildew-repelling agent, if you are able to. You can use this type of product on cedar decking and siding.

Things You Will Need

  • Spray canister
  • 3 quarts water
  • 1 quart bleach
  • ΒΌ cup liquid dishwasher detergent
  • Hose or power washer
  • Wood stain or preservative (optional)


  • Apply a sealant or wood stain only after you've rid the cedar of mildew completely. If any mildew is still present, it will grow through the stain and continue to spread.


  • Don't use a household detergent that contains ammonia. The ammonia and bleach combination will create a poisonous gas.
  • Avoid rinsing off the bleach solution before the 10 to 15 minutes are up. The bleach will not have enough time to kill all the mildew.