URBAN PLANTER BOXES

Short answer: yes, it can be okay, and in some urban planter boxes it is useful—but only when the plastic is installed as a liner rather than a sealed bathtub. A liner can protect wooden sides from damp soil, slow soil loss through gaps, and separate soil from metal or concrete. The risk is drainage. If water collects above the plastic, roots can suffocate and rot, especially in hot urban courtyards. Use a heavy-duty, UV-resistant HDPE or EPDM pond liner rather than thin sheeting or garbage bags. Press it into the corners, but make sure every existing drainage hole remains open. Ideally, slope the base slightly toward the holes, place a shallow layer of coarse gravel or lightweight aggregate over the liner, cover that with landscape fabric, and then add soil. This creates a drainage path while keeping fine particles out. For wooden boxes, line the sides and leave the bottom drainage clear; for metal boxes, avoid trapping water against the metal. If the planter has no drainage holes, add them before planting or choose a breathable lining. Check moisture regularly, and do not let the liner block air movement completely. For edible plants, use a known food-safe liner and avoid unknown recycled plastics. In short, plastic lining is acceptable and often helpful in an urban planter box, provided drainage, aeration, and durable materials are prioritized.