That's an excellent and practical question! The answer isn't a simple yes or no—it depends entirely on the cushion's material and construction. Always check the manufacturer's care label first; this is your most reliable guide.
Typically, cushions with removable covers made of fabrics like polyester, olefin, or solution-dyed acrylic are often machine washable on a gentle, cold cycle. Use a mild detergent and avoid bleach. However, many outdoor cushions have a fixed cover or contain non-removable foam inserts; these should never go in the washing machine as it can destroy the foam and stitching.
For most all-weather cushions, spot cleaning with a mild soap and water solution is the safest bet. For a deeper clean, you can often hose them down, scrub gently with a soft brush, and let them air dry completely in the sun. A key pro-tip: purchasing cushions with zip-off, machine-washable covers is the easiest way to simplify maintenance and keep your outdoor seating looking fresh season after season.