Whether you need a liner inside your wooden urban planter box isn't a simple yes or no—it depends on your goals for plant health and planter longevity. Generally, using a liner is highly recommended. Wood is porous and breaks down when constantly exposed to moist soil. A liner acts as a protective barrier, significantly extending the life of your planter by preventing rot. It also helps contain the soil and prevents staining from soil or fertilizer runoff on your balcony or patio.
However, proper drainage is non-negotiable. Never create a completely sealed, watertight environment. If using a plastic or pond liner, you must puncture several holes in its bottom, aligning with drainage holes in the wooden box itself. This allows excess water to escape, preventing root rot. For a more breathable option, many gardeners use landscape fabric. It allows water to drain while containing the soil and offering some protection.
Consider a layered approach: place a liner against the wood, ensure adequate drainage holes, and add a 1-2 inch layer of gravel or broken pottery at the very bottom before adding soil. This further improves drainage. For planters used for edible plants, ensure your liner material is food-safe. Ultimately, a well-installed liner protects your investment, maintains a healthier root environment, and makes your urban gardening project more sustainable and easier to maintain.