The short answer is: it's not recommended. While the durable, synthetic material of resin wicker can withstand weather, a power washer's intense pressure can be damaging. The high-pressure stream can force water deep into the weave, potentially trapping moisture inside the furniture frame, which can lead to mold, mildew, or rust on underlying metal parts. More directly, it can fray, crack, or splinter the resin strands, ruining the furniture's appearance and integrity.
For safe and effective cleaning, use a gentler method. Mix a solution of mild dish soap or a dedicated outdoor cleaner with warm water. Using a soft-bristled brush or a sponge, gently scrub the furniture. Then, thoroughly rinse it off with a garden hose on a gentle shower setting, ensuring all soap residue is removed. Always allow the furniture to dry completely in the sun before using it or adding cushions. This manual approach cleans effectively without risking the damage that a power washer's high-pressure jet can cause, extending the life of your outdoor investment.