The short answer is: it's not advisable to leave standard plush cushions on your outdoor furniture all the time. While convenient, doing so will significantly shorten their lifespan due to exposure to the elements. For long-term care, it's best to bring them in when not in use, especially during harsh weather or extended periods.
Standard plush cushions, often made from fabrics like cotton or velvet, are highly susceptible to damage from rain, sun, mold, and pests. Moisture is the primary enemy, leading to mildew, internal rot, and unpleasant odors. UV rays from the sun will fade colors and break down fibers, making fabric brittle.
To protect your investment, develop a routine of bringing cushions indoors or into a dry storage box when you expect rain or won't be using the furniture for several days. For daily use, consider investing in high-quality, all-weather cushions specifically designed for outdoor use. These are made from solution-dyed acrylics or polyester with quick-dry foam cores, offering much greater resistance to sun and water. Using a waterproof storage bench or dedicated deck box provides easy, accessible protection. For permanent setups, a fitted waterproof cover for the entire furniture set adds an extra layer of defense.
Ultimately, a little effort in cushion care goes a long way. Storing them properly preserves their comfort, appearance, and saves you money on frequent replacements, allowing you to enjoy your outdoor oasis for many seasons to come.