Yes—there are several urban planter box designs made to attach to a railing rather than sit on the floor. The most common are hook-over planters, which hang from the top rail with built-in metal hooks; clamp-on planters, which use adjustable brackets or C-clamps to grip the railing; and saddle or over-rail troughs, which straddle the top of the rail and often include liners and drainage trays. For smaller spaces, modular vertical planters can be hung from rails with straps or hooks, while heavier custom boxes may use stainless-steel brackets designed for the railing shape.
These designs are popular on balconies, terraces, and apartment railings because they save floor space and bring greenery closer to eye level. However, railing planters must be chosen carefully. Wet soil is heavy, so check the railing’s load capacity and the building’s rules before installing anything. Use lightweight potting mix and shallow boxes for herbs, flowers, and small greens. Make sure the planter is secured against wind, has drainage holes, and includes drip trays so water does not annoy neighbors. For glass railings, avoid clamping directly to glass unless the product is specifically rated for it; use rail-safe brackets or freestanding alternatives. Renters should prefer non-drilling hook-over or clamp-on models, while owners may choose bolted bracket systems for larger planters.
In short, yes: railing-attached planter boxes are widely available, practical, and well suited to urban gardening—as long as you match the design to your railing type and keep weight, drainage, and safety in mind.