Yes, using a liner inside your wooden urban planter boxes is a highly effective and common practice to protect them from rot and significantly extend their lifespan. The constant moisture from soil and water can quickly break down untreated wood. A liner acts as a protective barrier between the damp soil and the wooden walls.
For the best results, choose a liner material that is durable and allows for drainage, such as heavy-duty landscape fabric or polyethylene plastic (like a pond liner). Avoid non-porous materials without drainage modifications. Crucially, never completely seal the bottom. Always drill or punch drainage holes in the liner at the bottom of the planter, aligning with holes in the wood, to prevent waterlogged soil which harms plant roots.
Install the liner loosely against the wood, securing it only at the top rim. Leave a little slack to accommodate soil pressure. For extra protection, consider using a natural rot-resistant wood like cedar or redwood, and applying a safe, non-toxic sealant to the interior wood before adding the liner. This layered approach ensures your wooden planters remain sturdy and functional for many growing seasons, keeping your urban garden thriving.