Using treated wood for urban planter boxes intended for edible plants requires careful consideration. The primary concern revolves around chemical preservatives that may leach into soil and be absorbed by plants. Traditional pressure-treated wood containing chromated copper arsenate (CCA) has been phased out for residential use due to arsenic concerns. Modern pressure-treated lumber typically uses alkaline copper quaternary (ACQ) or copper azole, which are considered safer but still contain copper that can accumulate in soil over time.
For edible gardens, many experts recommend using naturally rot-resistant woods like cedar or redwood, or untreated wood with shorter lifespans. If using modern pressure-treated wood, consider lining the planter box interior with heavy-duty plastic (with drainage holes) to create a barrier between soil and wood. Another option is selecting wood treated with micronized copper, which has lower leaching potential.
Regular soil testing can monitor copper levels when using treated planters. Most safety concerns diminish when using wood produced after 2003, when CCA was discontinued for residential use. For maximum safety in vegetable gardens, untreated or naturally durable woods remain the preferred choice for long-term peace of mind.