Yes—an urban planter box can be used on a wooden deck without damaging the wood, but only if you treat it as a moisture-management and weight-management project rather than simply setting the box down. Wooden decks fail when trapped water, poor airflow, and constant damp contact soften the timber, encourage mold, or leave rust and tannin stains. The planter itself is rarely the problem; the way it drains and sits is.
Start by keeping the planter off the deck surface. Use sturdy pot feet, outdoor-treated timber offcuts, or planter risers to create a clear air gap. This lets the deck dry and prevents the base from sitting in a puddle after rain or watering. Put a drip tray or a waterproof liner under the box, but make sure the tray cannot overflow onto the wood. Ideally, direct drainage away from the deck or into a shallow tray you can empty. A liner inside the planter also protects the wood from soil moisture and keeps roots from touching the deck.
Choose a planter with good drainage holes and use a lightweight potting mix rather than dense garden soil. Urban planter boxes can become surprisingly heavy when wet, especially large ones, so place them near supporting beams or over joists and spread the load where possible. If the box is very large, use casters or a rolling base designed for decks, and check the deck's load capacity if you are unsure.
Finally, inspect the area every few weeks, especially after heavy rain. Wipe up spills, remove fallen leaves from around the base, and check for soft spots, discoloration, or mold. With an air gap, reliable drainage, a protective tray or liner, and sensible weight distribution, an urban planter box can sit on a wooden deck safely without causing damage.