No, urban planter boxes do not automatically need to be refinished or sealed every year. Annual maintenance is wise, especially in cities, but a full refinishing job should be based on condition, material, climate, and exposure rather than a rigid calendar. A well-made planter with a durable factory finish, composite boards, powder-coated metal, or sealed concrete may last several years between treatments. Untreated softwood, a rooftop box exposed to wind and freeze-thaw cycles, or a planter with poor drainage may need attention more often.
For wood planter boxes, inspect the surface in spring or early fall. If water still beads on the wood and the finish is intact, you can usually wait. If the wood looks gray, feels rough, drinks water quickly, develops cracks, or the old stain is peeling, clean it, sand lightly, and apply a suitable plant-safe penetrating oil, stain, or sealant. In many urban settings, wood may need a refresh every one to three years, not necessarily every year. Cedar, cypress, and thermally modified wood are more rot-resistant, but they still benefit from periodic protection. Avoid sealing wet wood, and let solvent-based products cure fully before replanting.
Metal and concrete planters have different schedules. Powder-coated metal generally needs only touch-ups when it is scratched or rusting, while concrete sealers often last a few years depending on porosity and weather. Urban conditions can speed up wear because planters face pollution, reflected heat, rooftop wind, irrigation splash, deicing salt, and freeze-thaw cycles. Good drainage matters as much as any finish. Standing water and soggy soil cause rot and finish failure faster than dry exposure does.
Sealing is not always the best fix. Some wood needs to breathe, and over-sealing can trap moisture and encourage rot. A breathable oil or stain is often better than a thick film finish. Always check drainage holes, add a liner when appropriate, and keep soil and mulch below the rim so water can move freely.
A practical rule is to inspect urban planter boxes every year, clean them as needed, test how the surface handles water, and refinish or reseal only when condition calls for it. So annual inspection is smart, but annual refinishing or sealing is not required for every planter box.