Pour baking soda over the grease stain on the cedar deck as quickly as possible. Allow the baking soda to absorb the grease stain while you gather other stain-removing supplies.
Mix 1/4 cup mild liquid hand dishwashing detergent with 1 gallon hot water in a bucket. Wear rubber gloves to protect your hands and mix the soapy solution with one hand.
Sweep up the baking soda with a broom and dust pan and discard the baking soda. Dip a scrub brush in the soapy solution and scrub the grease stain. Continue to dip the scrub brush in the soap water and scrub until the grease stain has lifted.
Rinse the area with plain water and towel dry so you can see if the grease stain has been fully removed.
Wash the cedar deck with a cleaning solution made from 2 tbsp. oxygen bleach detergent combined with 1 gallon hot water. Rinse the deck with plain water and allow it to fully dry.