Using pressure-treated wood for urban planter boxes where you grow food is a common question with a nuanced answer. Historically, lumber treated with chromated copper arsenate (CCA) contained arsenic and was deemed unsafe for direct contact with edible plants. However, since 2003, most residential pressure-treated wood uses safer preservatives like Alkaline Copper Quaternary (ACQ) or Copper Azole. These are considered low-risk, as the copper compounds bind tightly to the wood fibers.
For ultimate safety, experts recommend using 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, opt for naturally rot-resistant woods like cedar or redwood, or use untreated pine with the understanding it will have a shorter lifespan.
When building your planter, avoid using old, unknown treated wood which could be CCA. For new ACQ-treated wood, the risk is minimal, but using a liner provides peace of mind. Focus on filling your box with high-quality, organic soil for the healthiest harvest.