Protecting your wooden planter box from moisture and rot is key to its longevity. The right liner creates a crucial barrier between the damp soil and the wood. For most gardeners, a heavy-duty landscape fabric is an excellent choice. It's permeable, allowing excess water to drain while preventing soil from directly contacting the wood, which slows decay.
For boxes that will house moisture-loving plants or sit in very wet climates, an impermeable liner like a rubber pond liner or thick plastic sheeting can be used. The critical step here is to puncture several small drainage holes in the bottom to prevent waterlogging. Always ensure your planter box itself has adequate drainage holes as well.
Avoid using materials that trap too much moisture against the wood, like non-permeable plastic without drainage, as this can accelerate rot. Similarly, lining with old compost bags or thin trash bags often leads to premature failure. For a natural look, consider a coco coir or felt liner, but be aware these may break down faster. Ultimately, the best liner balances protection for the wood with a healthy root environment for your plants.