Yes—but usually not with a standard decorative planter. A Japanese maple can grow in an urban planter box only if the box is designed as a true tree planter rather than a lightweight street container. The planter must be large enough for the root ball and future roots, strong enough to hold saturated soil, the tree, and wind loads, and stable enough not to tip or bow.
For a small Japanese maple, choose a generously sized box—often at least 90–120 cm wide and deep, and larger for long-term growth. Dwarf or compact cultivars are much better suited to containers than full-size varieties. The material matters too: reinforced concrete, steel, thick timber, or a fiberglass planter with a steel frame is far safer than thin plastic or lightweight resin. Corners, base panels, and drainage openings need proper reinforcement.
Weight is a major issue. Wet soil is extremely heavy, and a tree adds more load, especially during wind. If the planter will sit on a roof, balcony, or deck, have the structure checked by a qualified engineer. Good drainage is essential because Japanese maples dislike waterlogged roots. Use drainage holes, a free-draining soil mix, and a slight air gap or gravel layer where appropriate. Dark metal planters can overheat roots in strong sun, so insulation or a lighter color may help.
Japanese maples also prefer shelter from harsh afternoon sun and drying wind. Keep the soil consistently moist but not soggy, mulch the surface, and protect the trunk from strong wind. In the long term, expect some root pruning and repotting or soil refreshment. So, would an urban planter box be strong enough? A standard decorative box probably not. A properly engineered, adequately sized, well-drained tree planter can be—provided it is matched to the tree’s mature size and the site’s structural limits.