The short answer is no, they do not always need seasonal oiling or staining as a fixed rule, but they do need seasonal attention. A wooden slat street bench exposed to sun, rain, frost, and everyday use will dry out and weather faster than indoor or covered furniture. In most climates, a deep clean and inspection every spring and autumn is enough, while oiling or staining is usually needed every 12 to 24 months rather than four times a year.
The real deciding factors are the wood type, the existing finish, and the local climate. Dense hardwoods like teak, ipe, or white oak are naturally weather-resistant and may only need regular cleaning with an occasional brightening or light oiling. Softer woods like pine, fir, or pressure-treated lumber usually need more consistent sealing to prevent cracking, splintering, and rot. If water no longer beads on the surface, or if the wood looks dry, faded, gray, or rough to the touch, it is time to reapply oil or stain.
The best routine is to wash the bench first with a wood cleaner or mild soap and water, removing dirt, mildew, and debris from between the slats. Let the wood dry completely. If the old finish is peeling or uneven, lightly sand the surface. Then apply a penetrating exterior wood oil or a semi-transparent stain with UV inhibitors. Two thin coats work better than one thick coat, and you should avoid heavy film-forming varnish or paint unless it is specifically designed for exterior wood, because trapped moisture can cause peeling and decay.
Seasonal oiling can actually do more harm than good if you overdo it. Excess oil sits on the surface, attracts dirt, and can become sticky or dark over time. A better habit is seasonal cleaning and inspection, with re-oiling or staining only when the wood actually needs it. In areas with harsh winters, coastal salt, or intense summer sun, check the bench before winter and again after the last frost.
So, street benches with wooden slats do not strictly require oiling or staining every season. What they need is regular cleaning and an honest seasonal check. Reapply oil or stain every year or two, or whenever the wood stops repelling water, and the bench will stay stronger, safer, and better looking for years.