Yes, an urban planter box can be used to grow a privacy hedge on a small deck, but it works best when the planter is treated as a miniature raised bed rather than a decorative pot. The key is to give the hedge enough root space, drainage, sunlight, and structural support while keeping the deck safe and usable.
For a small deck, choose a planter box that is at least 18 to 24 inches deep and wide enough for the mature root ball. As a rough guide, allow 40 to 60 gallons of soil volume per shrub, depending on the species and the privacy height you need. A planter box hedge will not usually match an in-ground hedge, so choose compact evergreens such as dwarf boxwood, Japanese holly, yew, or other slow-growing, upright shrubs that suit your climate. Bamboo can create fast privacy in an urban planter box, but only if it is a clumping variety and the planter has a sealed root barrier.
Drainage and weight are critical on a small deck. Use a planter with large drainage holes, pot feet, and a saucer or tray that directs water away from the deck surface. Fill it with lightweight, high-quality potting mix rather than heavy garden soil, and check that the deck can support the combined weight of the planter, wet soil, plants, and water. If you are unsure, ask a structural professional.
Install drip irrigation or a simple watering schedule, because planter box hedges dry out faster than garden beds. Prune lightly and regularly to keep the hedge dense and within bounds, and use a trellis or slim screen behind the plants if you need extra privacy while the hedge fills in. With the right planter size, compact evergreens, good drainage, and routine care, an urban planter box can create effective privacy on a small deck without turning the space into a crowded garden.