Whether you need a liner in your wooden urban planter box isn't a simple yes or no—it depends on your goals. A liner is highly recommended for longevity and plant health. It acts as a protective barrier between moist soil and the wood, significantly slowing rot and decay. This extends the life of your planter, especially with cheaper woods like pine. Liners also help contain soil, prevent nutrient loss from excessive drainage, and offer more control over moisture levels.
For most urban gardeners, using a liner is the wise choice. Opt for permeable materials like landscape fabric or recycled felt, which allow water to drain while holding soil. Ensure you create drainage holes in the liner that align with holes in the wooden box to prevent waterlogging. Avoid non-porous plastics directly against the wood, as trapped moisture can accelerate rot. If you prioritize a natural, unlined look and use rot-resistant wood like cedar, you can forgo a liner, but expect a shorter lifespan for the box itself. Ultimately, a proper liner is a small investment that protects your larger investment in the planter and your plants.