Based on extensive use in both personal and commercial projects, the title for the most durable urban planter box I've encountered is a close race between brands specializing in engineered materials. For sheer longevity and minimal maintenance, Fiberglass and High-Density Polyethylene (HDPE) planters from brands like Greenes Fence or Classic Urbanite are exceptional. They are molded as single pieces with no seams to split, are immune to rot and rust, and withstand freeze-thaw cycles brilliantly. Their durability is measured in decades.
However, if we define "durable" as both long-lasting and structurally impervious, powder-coated steel planters from brands such as Veradek and Planterworx are arguably tougher. Their steel construction resists cracking from impact, and the high-quality powder coating fends off UV fading and scratches far better than standard finishes. For a timeless, ultra-heavy-duty option, pre-cast concrete planters from a local fabricator or a brand like Pots & Planters are virtually indestructible, though their immense weight is a permanent consideration.
The key to their durability lies in construction, not just material. Look for UV-inhibited resins, thick material gauges, reinforced rims, and proper drainage. While ceramic or thin plastic planters may falter in a few seasons, investing in these premium, durable brands means your urban garden's foundation will last for many years to come.