Yes, using a liner for planter boxes on a wooden deck is highly recommended and often essential. The primary purpose is to protect your deck from moisture damage, which can lead to costly rot and structural issues. While not all liners are "special," selecting the right type is crucial.
A good liner serves two main functions. First, it acts as a root and soil barrier, preventing soil from directly contacting the wood and retaining moisture against it. Second, it helps manage water drainage. The liner should not be completely waterproof at the bottom; instead, it should have or allow for drainage holes. The key is to create a system where water drains *through* the planter in a controlled way, not seeping out the sides.
For optimal protection, consider a multi-layer approach:
1. Primary Liner: Use a durable, flexible pond liner or a heavy-duty plastic sheet as your main moisture barrier. Ensure it covers the entire interior.
2. Drainage Layer: Place a layer of gravel or hydro stones at the bottom of the liner before adding soil.
3. Root Barrier (Optional): For particularly vigorous plants, a separate root barrier fabric can add an extra layer of protection.
4. Elevated Base: Always place your planter box on pot feet or small blocks to elevate it off the deck surface. This ensures air circulation and allows drainage water to escape without pooling underneath.
By incorporating a proper liner and drainage system, you can enjoy your deck garden with peace of mind, knowing your wooden deck is safeguarded from prolonged moisture exposure.