About 1–2 weeks at 40°F (4°C) or below, according to USDA FoodKeeper v128. That window runs from the day you bought it — FoodKeeper publishes no separate after-opening figure for this one.
Does Swiss chard need to be refrigerated?
Yes — keep Swiss chard at 40°F (4°C) or below. Refrigerate at 40°F (4°C) or below.
How can you tell if Swiss chard is bad?
Look for: Sliminess or a wet film; Mould or dark mushy spots; Limp, shrivelled, or yellowing leaves; An off or sour smell. Never taste something to test it — when in doubt, throw it out.