Using treated wood for planter boxes intended for growing edible plants raises significant safety concerns that urban gardeners should carefully consider. Traditionally, wood was treated with chemicals like chromated copper arsenate (CCA), which contains arsenic—a known carcinogen that can leach into soil and be absorbed by plant roots. While CCA-treated wood is now restricted for residential use in many countries, newer treatments using alkaline copper quaternary (ACQ) or copper azole still introduce copper into the soil, which can reach toxic levels for plants and soil life.
For edible gardens, the primary risk is chemical migration from the wood into the soil and subsequently into your vegetables, herbs, or fruits. Even with newer treatments, the long-term safety for food crops remains debated. Health-conscious gardeners often choose untreated, naturally rot-resistant woods like cedar or redwood, or alternatively use composite lumber, food-safe plastic containers, or metal planters with proper lining. If using older treated wood, assume it contains harmful chemicals and avoid it for edibles entirely. For any planter construction, adding a heavy-duty plastic liner as a barrier between the wood and soil can provide an additional layer of protection, though it may not be completely foolproof over time. Prioritizing known safe materials ensures your urban harvest remains healthy and uncontaminated.