Many urban gardeners wonder about the safety of using treated wood for planter boxes containing edible plants. The concern stems from chemicals used in wood preservation processes that could potentially leach into soil and be absorbed by plants.
Historically, wood treated with chromated copper arsenate (CCA) raised significant health concerns due to arsenic content, leading to its phase-out for residential use in 2003. Modern pressure-treated lumber typically uses copper-based preservatives like ACQ (Alkaline Copper Quaternary) or CA-B (Copper Azole), which are considered safer alternatives.
Research indicates that while these copper-based treatments can leach small amounts of copper into soil, the levels rarely reach concentrations harmful to human health, especially when proper precautions are taken. The amount of copper absorbed by plants varies by species, with root vegetables typically accumulating more than leafy greens or fruiting plants.
To minimize any potential risk, experts recommend several safety measures: using a heavy-duty plastic liner between the wood and soil, selecting wood labeled for garden use, avoiding fresh treated wood for edible gardens, and considering naturally rot-resistant alternatives like cedar or redwood. For those particularly concerned, using untreated wood with a non-toxic sealant or opting for alternative materials like food-grade plastic or metal planters provides peace of mind.
Regular soil testing can help monitor copper levels, and adding organic matter to soil can help bind copper particles, reducing plant uptake. With proper precautions, modern treated wood can be a viable option for urban planter boxes, though many gardeners prefer untreated alternatives for complete peace of mind when growing edibles.