When building planter boxes for an edible urban garden, the safety of construction materials is paramount. Many gardeners ask: is it safe to use pressure-treated wood? The answer depends heavily on the type of treatment used.
Historically, wood treated with Chromated Copper Arsenate (CCA) contained arsenic and was deemed unsafe for direct contact with edible plants. However, CCA has been phased out for residential use since the early 2000s. Modern pressure-treated lumber for consumer use typically employs alternative preservatives like Alkaline Copper Quaternary (ACQ) or Copper Azole. These are considered much safer, as they use copper as the primary fungicide without arsenic or chromium.
While the risk from modern treatments is low, a cautious approach is wise. For absolute safety, use a heavy-duty plastic liner as a barrier between the treated wood and your soil. This prevents any potential chemical leaching. Ensure the liner has drainage holes. Alternatively, consider using naturally rot-resistant woods like cedar or redwood, or composite lumber made from recycled plastics.
The soil's pH also plays a role. Slightly acidic soil can increase the potential for copper to leach from ACQ-treated wood. Maintaining a neutral pH (around 6.5 to 7.0) can help minimize this. Ultimately, using modern, labeled "safe for garden use" treated lumber with a proper liner is a common and generally accepted practice for building durable, long-lasting edible garden planters in urban settings.