Choosing the correct liner for your wooden urban planter boxes is crucial for plant health and the longevity of the box itself. The primary purpose of a liner is to protect the wood from constant moisture and soil contact, which causes rot and decay. It also helps contain the soil and prevent it from washing out through drainage gaps.
Your best options are permeable landscape fabric or a durable plastic liner with added drainage holes. Landscape fabric is an excellent choice as it allows water and air to pass through while holding soil in place. It's easy to cut and fit. For a plastic liner, use a heavy-duty polyethylene or pond liner. Crucially, you must puncture several holes in the bottom of any non-permeable liner to ensure proper drainage and prevent waterlogged soil, which kills plant roots.
Avoid using materials that degrade quickly, like trash bags or newspaper. Also, consider adding a 1-2 inch layer of gravel or pebbles at the bottom of the lined planter before adding soil. This layer further improves drainage. A well-chosen liner will shield your wooden planter, promote healthy root growth, and make your urban gardening project a lasting success.