If you need one answer: specify a precast reinforced-concrete planter box with an integral, sloped drainage floor, stainless-steel drain grate, replaceable inner liner, and anti-graffiti sealer. In a busy public plaza, durability is less about one material and more about how the planter handles impact, weather, vandalism, cleaning, and drainage—but reinforced concrete consistently wins on all four.
Concrete planters are heavy, stable, and highly resistant to kicks, carts, skateboards, and concentrated impacts. They do not rust, rot, or become brittle under UV the way steel, wood, and fiberglass can. With air-entrained concrete and proper reinforcement, they can handle freeze-thaw cycles and de-icing salts. Chamfered edges reduce chipping, while a smooth, sealed finish makes graffiti easier to remove. A sloped internal floor and stainless-steel drainage prevent waterlogged roots and cracked walls. If the plaza needs vehicle protection, concrete planters can also be engineered as barriers.
Powder-coated steel is a strong second choice where weight matters. It is tough and repairable, but scratches can lead to corrosion, and large dents are hard to fix. Fiberglass is lightweight but can crack, fade, and delaminate; wood rots and needs regular maintenance. For a high-traffic public space, those weaknesses usually shorten service life.
Do not ignore detailing. Specify minimum 5,000 psi concrete, adequate reinforcement, freeze-thaw durability where needed, heavy-duty stainless hardware, and a replaceable liner so plants and soil can be renewed without replacing the box. Check structural loading and drainage connections before installation. With that specification, a precast reinforced-concrete planter should deliver the longest, lowest-maintenance service life in a busy public plaza.