It's a lovely idea to add comfort to your garden bench with a fabric cushion, but leaving it outside permanently is often a recipe for disappointment. While not inherently a "bad" idea, it's a high-maintenance one that requires the right materials and consistent care. Standard fabrics will quickly fall victim to rain, leading to mildew, and sun, which causes fading and fiber degradation. The constant dampness can also rust or warp your bench frame.
For success, you must start with cushions specifically designed for outdoor use. Look for labels like "weather-resistant," "all-weather," or "solution-dyed acrylic." These fabrics dry quickly, resist mildew, and have UV inhibitors to prevent fading. Even with these, proactive care is non-negotiable. You should shake them off regularly, clean spills immediately, and store them indoors during prolonged harsh weather or off-season.
A more practical alternative is to use removable cushions. Treat them like you would an outdoor umbrella—enjoy them when you're outside and store them in a deck box or garage when not in use. This simple habit dramatically extends their life. For a truly hands-off approach, consider built-in bench seats made from slatted wood or choose cushions with a quick-dry foam core and a waterproof liner. Ultimately, a permanent fabric cushion can work, but only if you invest in premium outdoor-grade products and commit to their upkeep. Otherwise, opting for easy-to-remove comfort or alternative materials will save you time and money in the long run.