Treated Lumber in the Garden: Is It Safe for Edibles and Ornamentals?
A common question among new gardeners building raised beds is, “Can I use treated lumber for raised beds or container gardening?” The short answer is yes—but with a few important considerations.
The Appeal of Wood in the Garden
Wood is a popular choice for garden structures because it’s affordable, easy to work with, and readily available. But when it comes to choosing the right wood, things can get a bit tricky.
- Untreated wood like pine is safe for growing food, but it breaks down quickly when in contact with soil—often rotting within a year.
- Naturally rot-resistant woods such as cedar, redwood, and certain hardwoods last longer and are also safe, but they’ll eventually succumb to decay too.
Why Treat Wood?
To extend wood’s life, especially in damp or pest-prone environments, it’s often treated with preservatives. Historically, people used plant oils and tars like pine tar to keep moisture and bugs at bay. These natural coatings worked to some extent but required frequent reapplication.
In the 18th century, the British Royal Navy went a step further—coating ships with copper to prevent barnacles and shipworms. Copper, while essential to plant health in small amounts, is toxic in high concentrations—a good reminder that balance is key, even in the garden.
A Brief History of Treated Lumber
By the 1940s, wood treatment had become a science. Pressure-treated lumber became common, with chemicals like chromated arsenicals, creosote, and pentachlorophenol used to make wood incredibly durable. However, these treatments leached toxic substances into the soil and water, making them unsuitable for food gardens.
The most widely used preservative during the late 20th century was chromated copper arsenate (CCA). While effective, it contained arsenic—a known carcinogen. In response to health and environmental concerns, CCA was banned from residential use in the U.S. as of December 31, 2003.
What About Today’s Treated Lumber?
Since 2004, treated lumber sold for residential use in the U.S. has been treated with ACQ (alkaline copper quaternary)—a water-based preservative that guards against fungal decay and insect damage. ACQ is considered safe for gardens, including food production, and is approved by the FDA.
There is a catch, though: ACQ-treated lumber doesn’t last as long in direct soil contact as the older (toxic) treatments once did.
Tips for Safe Gardening with Treated Lumber
- Use only treated lumber labeled safe for residential or garden use—this means post-2004 ACQ-treated wood.
- Avoid repurposing old lumber—especially if you don’t know when or how it was treated.
- Create a barrier—if you want extra peace of mind, line your raised beds with heavy-duty plastic sheeting to keep soil from directly touching the wood.
- Consider alternatives—composite or recycled plastic lumber is long-lasting and safe, though it can be more expensive upfront.
Final Thoughts
Treated lumber can be a safe and practical choice for your garden—as long as you know what you’re working with. Stick to modern, ACQ-treated wood or other safe materials, and your raised beds, trellises, or planters can thrive for years to come.
Happy gardening!
