Many urban gardeners wonder about the safety of using pressure-treated wood for their planter boxes, and this concern is both valid and important. Pressure-treated wood has been chemically treated to resist rot, insects, and decay, making it durable for outdoor use. However, the chemicals used in this treatment process can potentially leach into soil and affect plants.
Historically, pressure-treated lumber contained chromated copper arsenate (CCA), which included arsenic - a known carcinogen. Since 2003, most residential pressure-treated wood has switched to safer alternatives like alkaline copper quaternary (ACQ) or copper azole, which don't contain arsenic. While these newer treatments are generally considered safer, they still contain copper compounds that can accumulate in soil over time.
For vegetable gardens, the risk depends on what you're growing. Root vegetables like carrots and potatoes are more likely to absorb chemicals than above-ground crops like tomatoes and peppers. Many experts recommend using a heavy plastic liner between the wood and soil to minimize contact, though this doesn't eliminate all risk.
If you're concerned about chemical exposure, consider these alternatives: naturally rot-resistant woods like cedar or redwood, composite lumber, or metal planters. For existing pressure-treated planters, adding a barrier and replacing the top few inches of soil annually can reduce potential contamination.
Ultimately, while modern pressure-treated wood poses less risk than older varieties, many gardeners prefer erring on the side of caution, especially when growing edibles. Your decision should balance durability needs with your comfort level regarding potential chemical exposure in your urban garden.