Pressure-treated wood is a popular choice for outdoor projects, including raised garden beds, due to its durability and resistance to rot and pests. However, studies have raised concerns about the potential health and environmental risks associated with the chemicals used in the treatment process.
The most common preservative used in pressure-treated wood, chromated copper arsenate, contains arsenic, a known carcinogen.
As gardeners, it’s crucial to understand the potential dangers of using pressure-treated wood in our gardens and explore safer alternatives to ensure the health of our plants, our families, and the environment.
What Is Pressure-Treated Wood?
Pressure-treated wood undergoes a process that infuses the lumber with chemical preservatives under high pressure. This makes the wood more durable and resistant to rot, decay, and insect infestation compared to untreated wood.
The most common preservatives used are chromated copper arsenate (CCA), alkaline copper quaternary (ACQ), and copper azole (CA). (ref) While newer copper-based treatments are considered less toxic than CCA, which was phased out for residential use in 2003, they still contain chemicals that can potentially leach into soil.
The Troubling Truth about Chemical Leaching
Despite the wood treatment industry’s claims that the chemicals in pressure-treated wood become fixed and unlikely to leach out, numerous studies have shown otherwise. (ref) Here are some key findings:
- Arsenic, copper, and chromium from CCA-treated wood can leach into the surrounding soil, with the greatest concentrations found within a few inches of the wood.
- Leaching is most pronounced during the initial exposure to the elements, especially rainfall, but continues at a slower rate over the lifespan of the wood.
- Acidic soil conditions and organic acids produced during composting can increase the leaching of preservative chemicals.
- While the amounts of arsenic and other chemicals that transfer into crops appear to be low, any level of exposure from homegrown produce is concerning.
Risks to Your Health and the Environment
Arsenic is a known human carcinogen, and exposure has been linked to various health problems, including skin, bladder, and lung cancers. Copper, while an essential nutrient in small amounts, can be toxic to aquatic life.
The production and disposal of pressure-treated wood also raises environmental concerns.
Although the risks from eating vegetables grown in beds made with treated wood may be small for individuals, it’s still an unnecessary exposure that is best avoided, especially for children who are more vulnerable to the effects of toxins.
Additionally, using this wood contributes to the continued manufacturing and eventual disposal of a product that poses ecological hazards.
Safer Alternatives for Your Garden Beds
Luckily, there are several options for constructing raised beds without resorting to pressure-treated lumber:
- Naturally rot-resistant wood: Cedar, redwood, and black locust are examples of woods that have a natural resistance to decay and insects, making them good choices for garden beds.
- Recycled plastic lumber: Made from recycled HDPE plastic, this wood alternative will not leach any chemicals and is highly durable.
- Concrete blocks, bricks, or stones: These inert materials can be used to create long-lasting beds that won’t contaminate your soil.
- Untreated wood with a liner: If using untreated wood, you can line the interior of the bed with heavy plastic to create a barrier between the soil and wood.
- Mounded soil beds: Forgo any framing and simply mound the soil into raised beds, avoiding the need for treated wood altogether.
When it comes to the garden you pour your heart into and the food you feed your loved ones, it’s not worth taking chances with pressure-treated wood. By choosing a safer material for your raised beds, you can have peace of mind knowing that you’re eliminating a potential source of contamination.
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Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.