Urban planter boxes are typically made from concrete, metal, wood, plastic or HDPE, fiberglass or composite, and sometimes natural stone or terracotta. Concrete and stone are common in streetscapes and plazas because they are heavy, stable, and resistant to wind and vandalism. Metal planters—such as powder-coated steel, galvanized steel, aluminum, or weathering steel—offer a modern look, are relatively lightweight, and work well in modular systems. Wood, especially cedar, teak, or ipe, provides a warm appearance but needs protective finishes and may rot over time. UV-stabilized HDPE and fiberglass or composite planters are popular because they are light, rot-proof, and low-maintenance. Terracotta and ceramic are more decorative and less common in heavy public use.
For the longest outdoor lifespan, precast reinforced concrete—or natural stone where weight and budget allow—usually lasts the longest. Properly designed concrete planters can remain serviceable for decades, though freeze-thaw cycles, poor drainage, and root pressure can cause cracks. Among lighter materials, UV-stabilized HDPE and high-quality fiberglass or composite are excellent long-term choices because they do not rot and resist moisture and insects. Marine-grade stainless steel or well-protected galvanized steel can also last a very long time, but scratched coatings and ordinary steel may rust. Wood has the shortest lifespan unless it is a durable species with regular maintenance.
So the practical answer is: concrete or stone lasts longest overall in urban outdoor conditions; HDPE and composite are the best long-lasting lightweight alternatives; metal needs careful coating and maintenance; wood is attractive but requires more care.