Treated lumber is a popular choice for building raised garden beds, as it is affordable, easy to work with, and resistant to rot, fungi, and other pests. However, the use of treated wood can lead to chemicals leaching into the soil, which could be harmful to plants. The main concern with treated wood is the potential for chemicals used in the treatment process to leach into the soil, which could then be absorbed by plants. This is particularly concerning for beds used for growing edible plants.
Alkaline copper quaternary (ACQ) is a relatively new chemical treatment that is safe for use in vegetable gardens. However, CCA-treated wood, which contains copper, chromium, and arsenic, is no longer available for residential use as of 2004. The ACQ treatment is considered safer for use in raised garden beds, but it is important to preserve it if you want to maintain organic practices.
When using treated wood for garden beds, it is essential to seal the lumber, use a good plastic liner, and plant edibles in the middle of the bed. However, safe practices recommend not using treated wood where it may come into direct or indirect contact with drinking water or a component of food, animal feed, or beehives. The USDA prohibits treated lumber for soil contact use in their certified National Organic Program published in 2011.
Most modern treated lumber is now MCA-C treated (Micronized Copper Azole), approved for fresh water contact. Although newer, safer treated wood is considered safe, Wolmanized Outdoor does not recommend using pressure-treated wood for garden beds. In summary, using newer, safer treated wood for non-edible plants with proper precautions like barriers is recommended. While the risks to human and environmental health are still present, the “new” pressure-treated wood is safe for use in raised garden frames with a few precautions.
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📹 DON’T Use Pressure Treated Wood in Raised Garden Beds
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Gratitude from Flagstaff, AZ! While our high mountain, short season climate is pretty opposite yours in Broward County, FL, I have thoroughly enjoyed your articles. I am very familiar with Regen Ag and have been organic gardening for 40+ years, and I have found great pointers and new ideas from your articles. This article on pressure treated wood was informative. My raised beds (with pine boards) will be 4 years old this summer and are still in good shape, though beginning to show some rot – the benefit and downfall of high altitude desert gardening! I may start replacing them with cedar, one at a time over the next few years. Thanks for your informative articles, excellent production quality and very friendly approach. It’s a joy to watch. Thanks and keep up the great work!
Great article! Succinct and to the point. I’m just a home gardener not looking to be certified organic so I have used PT GC for my raised beds for many years now (post 2004). When we moved back to AL in 2010 I did a lot of research into this subject and spoke with our local extension office which provided me with additional resources to look into. The end result was that I landed exactly at the same conclusion that your excellent article points out. I did not use a barrier on the inside of the raised beds but instead, I built them in the fall and allowed them to sit out over the winter and filled them with soil in early spring. My thinking was that I would allow the treatment to leach and dissipate over time. The extension office pointed me to research that showed that any leaching happens just a couple of inches from the wood. Even with using PT wood, I need to replace my old beds and build new ones this fall. I will try the plastic liner on the sides facing the soil and see how long it lasts. Thanks again for your article and I appreciate your non-condescending approach to presenting the subject matter.
I’m eliminating plastic from my gardeing as possible because plastic leaches. I’ve read some concerning articles about the microplastic pollution in organically produced food. It seems switching from pesticides and herbicides to plastic wasn’t a good solution. Due to my family’s autoimmune health problems we are exceedingly careful about how we grow our food. I appreciate your scientific analysis about treated wood. Is there risk of bio accumulation over time with the copper?
I have a ton of treated lumber from old decking I had to remove. Amazingly it’s still usable so I repurposed some of it around the property. Unfortunately I can’t remember if I got it back in 2003/2004 or right around when the change was taking place. We have some raised beds but I used redwood. Now we are planning another raised bed for another other plant and veggie garden, but had some second thoughts about the pre 2004 lumber, but like you said I will still check the tags that might still be stuck on the ends.
Humans have been working with and using copper since the copper age starting around 5000bc, since then we have used this metal in everything including pennies, pots, buckets, water pipes, wires, toys, jewelry, roofs, and much more. It’s also been used in gardens for decorative purposes and as an organic fungicide. Copper treated wood has been used extensively in decks, gardens and playgrounds since the early 2000s. It is also an essential mineral for both plants and humans. Like almost everything, too much copper exposure can be toxic. Yet with all this copper in our lives copper poisoning or copper toxicity in humans remains extremely rare. On the list of things to be worried about, copper poisoning from garden beds should be very low.
I recently built a few beds with redwood 2x12s held together using dovetails and dowels so there are no screws to rust or pull out. The boards were $8/ft for full dimension 2x12s plus tax and a few dollars for oak dowels. It was not cheap, about $100 for a 2’ by 4’ bed but hopefully they hold up for many seasons and I can grow a lot of food in them. If they last for 10 years it’s only $10 per year which isn’t much more than buying plastic pots or other raised bed options. If they last 15-20 years the cost per year is almost nothing at that point. Quality pays for itself if you are planning on using them for the long term.
Perhaps a little more research on plant take-up of the chemicals involved instead of the process of how the wood is treated would be more helpful to gardeners. A simple search of published research found me this. The first is a quote from a paper out of Penn State extension and the second is a link to the paper. I think viewers will find what they need to know. I realize youtube is about getting clicks and catchy titles do that, but I appreciate content more….. Very few studies have analyzed plants grown in close proximity to CCA-treated wood. The Hickson Corporation, a manufacturer of CCA-treated wood, analyzed carrots, okra, peppers, cucumbers, and tomatoes grown in raised beds made with CCA-treated wood. They found that As, Cr, and Cu contents were in the same range as those of vegetables purchased at a grocery store or grown in raised beds made with untreated wood. Analysis of grapes grown adjacent to CCA-treated stakes showed no increase in As, Cr, or Cu.4 Romaine lettuce grown in pots with soil that contained small (approx. 1 inch) cubes of CCA-treated wood showed increased uptake of As such that a normal serving (50 g) would contain 0.004 mg of As.5 This compares to the normal dietary intake of 0.004-0.01 mg of inorganic As and the estimated safe intake level of 0.05 mg of inorganic As. The average adult would have to eat over 1.3 pounds of this romaine lettuce every day to exceed the estimated safe intake level of As. extension.psu.edu/environmental-soil-issues-garden-use-of-treated-lumber