Honestly, there is not one magic number that works for every bench, but most wooden outdoor benches need to be re-stained or resealed every 1 to 3 years. The exact timing depends on the type of wood, the finish you use, your local weather, and how much sun and rain the bench gets.
If your bench sits on a covered porch in a mild climate, it may only need attention every 2 to 3 years. If it is fully exposed to harsh sun, snow, or heavy rain, you will probably need to re-seal it every 12 to 18 months. A simple test is the water bead test: sprinkle a few drops of water on the wood. If the water beads up, the seal is still working. If it soaks in and darkens the wood, it is time to clean and recoat.
Hardwoods like teak, ipe, or white oak hold up better and can often go longer between treatments. Softwoods like pine or cedar are more porous, so they usually need sealing more often. Cedar is naturally rot-resistant, but it still fades to gray and benefits from a protective coat every 1 to 2 years if you want to keep its color.
The type of finish matters too. A penetrating oil or sealer typically lasts about 1 to 2 years. Film-forming stains, like solid stains or deck stains, can last 2 to 3 years but may peel if the wood was not prepped well. Spar varnish or marine varnish offers more water resistance but can crack under UV exposure and generally needs sanding and recoating every 2 years or so.
Before re-staining or sealing, always clean the bench first. Use a wood cleaner or a mild soap-and-water mix with a soft brush, rinse it, and let it dry completely. Lightly sand any rough spots or peeling areas. Never apply a new coat over dirt, mildew, or flaking finish, or it will fail quickly.
Also watch for visual signs rather than sticking only to a strict calendar. If the wood looks dry, faded, gray, or rough to the touch, it is time to reapply. If water no longer beads, if you see small cracks or raised grain, or if the original color has washed out, do not wait for a set date.
In short, plan for every 1 to 2 years for exposed softwood benches, every 2 to 3 years for hardwood or sheltered benches, and always let the condition of the wood guide you. That approach will keep your bench protected, safe from rot, and looking far better season after season.