Whether you need a liner for your urban planter box depends on its construction material. The primary purpose of a liner is to protect the box from moisture damage and, in some cases, to prevent soil contact with questionable materials.
For wooden planters, especially those made from cedar or redwood which are naturally rot-resistant, a liner is highly recommended to extend their lifespan. You have several effective options:
1. Landscape Fabric or Weed Barrier: This is often the best choice. It's permeable, allowing water to drain freely while containing the soil. It prevents soil from washing out and helps protect the wood from constant moisture.
2. Plastic Sheeting or Pond Liner: Use this with caution. While it provides excellent waterproofing, you *must* puncture drainage holes in the bottom to prevent waterlogged soil, which leads to root rot. Avoid lining the sides completely to allow for some air circulation.
3. Built-in Coating: Some planters come with a plastic or metal interior coating, which serves as a ready-made liner.
For plastic, metal, or composite planters, a separate liner is usually unnecessary as these materials are already waterproof and durable. The focus should be on ensuring adequate drainage holes at the bottom.
A critical step, regardless of liner choice, is to add a 1-2 inch layer of coarse gravel or stones at the bottom of the planter before adding soil. This layer, beneath the liner, creates a drainage reservoir and further prevents the drainage holes from clogging.
In summary, for long-lasting wooden urban planters, use a permeable landscape fabric liner combined with a gravel drainage layer. This setup protects your investment, ensures proper drainage, and creates the ideal environment for your plants to thrive.