Plastic outdoor benches are pretty low-maintenance, but the wrong cleaner or scrubbing pad can leave behind chalky patches, streaks, or fading. The safest approach is to start gentle and only move up if you actually need to.
Start by rinsing the bench with a garden hose to remove loose dirt and dust. Then fill a bucket with warm water and add a few drops of mild dish soap—nothing with bleach or strong degreasers. Dip a soft microfiber cloth or non-abrasive sponge into the soapy water, wring it out, and wash the bench in small sections. If you are cleaning a colored or dark bench for the first time, test the soapy water on a hidden spot and let it dry before doing the whole surface.
For stains like bird droppings, tree sap, or mildew, mix baking soda with a little water to make a paste. Apply it gently with a soft cloth, rub in a circular motion, and rinse thoroughly. For mildew, a 50/50 mix of white vinegar and water works well, but never combine vinegar with bleach or other cleaners. Rinse the bench completely after any treatment because residue can cause uneven fading.
After cleaning, dry the bench with a clean microfiber towel or let it air-dry in the shade. Avoid harsh brushes, magic erasers, bleach, ammonia, and undiluted vinegar, because they can break down the plastic surface and make discoloration worse over time. To keep the color stable, park the bench out of direct afternoon sun when possible or use a UV protectant made for plastic outdoor furniture.
A gentle wash every few weeks plus a good rinse after storms or pollen season is usually all you need to keep a plastic bench looking bright without bleaching or yellowing it.