Yes. An urban planter box can be used on a gravel roof without puncturing the waterproof membrane, provided it is installed as a non-penetrating, protected system rather than fastened through the roof. The key is to keep the planter and its loads separated from the membrane and to avoid any screws, anchors, or stakes that pass through the roofing layers.
A suitable setup usually includes a protective separation layer such as a geotextile or slip sheet, rigid protection such as pavers or a pedestal system, and a freestanding planter with its own base. The planter should be raised so water can drain freely, and it should not block roof drains or create ponding. Because gravel roofs are ballasted and can hide the membrane, workers should move gravel carefully and inspect the membrane before installation.
Weight, wind uplift, and maintenance matter. Soil is heavy when wet, so confirm the roof’s structural capacity with a qualified engineer. In exposed locations, use a ballasted or otherwise restrained planter design that does not rely on membrane-penetrating fasteners. Choose a planter with drainage, a root barrier where needed, and access for inspection. Also check local codes, insurance requirements, and warranty terms with the roofing manufacturer.
In short, yes—an urban planter box is possible on a gravel roof without puncturing the membrane if it is designed as a protected, freestanding, non-penetrating installation and reviewed by a structural and roofing professional.