The short answer is yes, you can leave quality wrought iron furniture outside during winter, but it requires proper preparation and care to prevent damage. Wrought iron is durable and heavy, making it resistant to wind, but its main enemy is moisture, which leads to rust.
To protect your furniture, start with a thorough cleaning. Wash off dirt and grime with mild soap and water, and let it dry completely. Inspect for any existing rust spots; sand them down and touch up with matching rust-inhibitive paint. The most critical step is applying a protective wax or sealant designed for metal outdoor furniture. This creates a barrier against snow, rain, and salt.
Using a waterproof, breathable furniture cover is highly recommended. Ensure the cover fits well and is secured to prevent moisture buildup and wind from whipping it against the metal, which could cause scratches. Avoid plastic tarps that trap condensation, as this promotes rust. If possible, place furniture in a slightly sheltered area, like under a deep eaves or a patio cover, to reduce direct exposure to the elements.
Even with covers, check on your furniture periodically during mild winter days. Remove heavy snow accumulation to prevent undue stress on the joints. Come spring, clean it again and inspect for any issues that need addressing before the season's use.
With these proactive steps, your wrought iron furniture can withstand winter weather and remain a beautiful part of your outdoor space for many seasons. Neglecting preparation, however, can lead to costly repairs or replacement due to accelerated rust and corrosion.