Yes, using a liner in a wooden urban planter box is highly recommended to significantly extend its lifespan by preventing rot. While durable woods like cedar or redwood have natural rot resistance, constant exposure to moist soil and water will eventually cause decay. A liner creates a crucial protective barrier between the damp soil and the wood.
You have several effective liner options. A simple and common method is to use a heavy-duty plastic sheet or a pond liner, ensuring you puncture holes in the bottom to align with the planter's drainage holes. This allows excess water to escape while shielding the wood. Alternatively, you can use a commercial plastic or fabric grow bag placed inside the box. For a more natural approach, applying a non-toxic waterproof sealant directly to the interior wood surfaces is also effective.
Regardless of the liner choice, proper drainage is non-negotiable. Ensure your planter box has adequate drainage holes at the bottom. Adding a layer of gravel or pebbles beneath the liner can further improve drainage and air circulation. Combining a reliable liner with good drainage practices will protect your investment, keeping your wooden planter boxes structurally sound and beautiful for many growing seasons.