The answer to whether you can leave urban outdoor furniture outside all winter isn't a simple yes or no. It primarily depends on the material. True all-weather materials like powder-coated aluminum, teak, and certain high-quality synthetic resins (HDPE) are designed to withstand freezing temperatures, snow, and moisture. They can typically remain outdoors if properly cleaned and, for some, covered with a breathable, waterproof cover.
However, furniture made from materials like standard iron (which can rust), untreated wood (which can warp and crack), or cushions with non-weather-resistant fabric must be stored indoors for winter. Even for all-weather pieces, best practice involves a thorough cleaning to remove dirt and debris that can trap moisture, applying protective oil for woods like teak, and using fitted covers to shield from heavy snow load and UV degradation. Storing cushions and textiles indoors is always recommended.
Ultimately, consulting the manufacturer's care instructions is crucial. When in doubt, storing furniture in a dry, covered space like a garage or shed will maximize its lifespan and keep your urban oasis looking its best for seasons to come.