There is scientific consensus that treated wood can be used for garden and vegetable beds. Current research confirms treated wood has no impact on plants and produce.
The information below explains what preservative components are used in Viance ground contact treated wood intended for residential use and the results of numerous scientific studies.
The AWPA Book of Standards, lists copper azole (CA)for ground contact applications in Use categories UC4A, UC4B and UC4C. CA is widely available under the brand name Preserve® and is sold at 84 Lumber and independent lumber dealers across North America.
The CA preservative contains copper, the primary fungicide and termiticide in Viance’s residential ground contact product. The fungicide prevents soil fungi from attacking the lumber and works to deter insects, including termites. Copper is also a common fungicide for food crops used by consumers for growing vegetables and is a disinfectant in swimming pool chemicals.
Of interest to the home gardener is whether any of the preservative components in treated wood used to construct a raised bed garden could render the food crop unsafe for consumption. The current evidence confirms those concerns are unwarranted.
Current Research Study – April 17, 2024, Update
After three growing seasons, Oregon State University (OSU) researchers Presley and Konkler concluded “that no increase in copper concentration was detectable in vegetables grown in garden boxes made with CA-C treated wood over vegetables grown in untreated beds.” Dr. Gerald Presley, lead researcher on the project further stated that the study tested soil samples and vegetables from the garden boxes in a laboratory to determine copper levels. The data confirms treated wood used to build raised beds for gardening has no impact on the amount of copper found in plants grown in the beds.
Read the complete study in the article available in the Wood and Fiber Science Journal.
Research Study – April 17, 2023, Update
Dr. Gerald Presley, Assistant Professor at Oregon State University, began a small-scale study in 2020 on metal leaching in treated wood garden boxes. After two growing seasons, eleven types of garden vegetables have been analyzed for copper content. These include arugula, basil, beets, carrots, kale, lettuce, parsnips, peas, radishes, tomatoes, and turnips. None of the vegetables grown in beds made with copper azole treated wood showed elevated copper levels compared to vegetables grown in beds constructed with untreated wood.
Research Study – February 24, 2022
Dr. Gerald Presley, Assistant Professor at Oregon State University, began a small-scale study in 2020 on metal leaching in treated wood garden boxes. After one year, the data shows no difference in copper (Cu) content in vegetable matter harvested from treated or untreated boxes. Dr. Presley will plant each year, rotating crops, and monitor metals over a 4 to 5-year period. The goal is to annually sample soil and crops to build a large, long-term dataset on many vegetables over the life of a garden box. Dr. Presley explains, “We still have a few more samples to process from year one, but from what we see now there does not appear to be any measurable impact of treated wood garden boxes on metal levels in vegetables.” Annual data from this study will be presented at the American Wood Protection Association meeting and published in the proceedings. Data will also be available to members of the Environmental Performance of Treated Wood Research Cooperative in annual reports.
Prior Research
John Harrison, President of JRH Toxicology, a consulting firm specializing in scientific advice to the industry and government, writes in 2017 that CA and ACQ have been carefully evaluated for safety and registered by the Health Canada Pest Management Regulatory Agency (PMRA) for use in residential construction applications. He stated in a bulletin titled, Treated Wood in Raised Bed Gardening, “Scientific evidence and data have shown that using pressure treated wood for raised bed or box gardening is safe to adults and children in terms of the plants grown and used in these containers.” He further explains, “All chemicals in consumer products have a toxicity and most are very low, so they are not a problem, especially those regulated by the federal government. This is also the case with currently registered wood preservatives that contain copper. In fact, small amounts of copper are necessary for human and plant life and termed “an essential trace element”.
In a 2014 study, wood research scientists Love, Gardner and Morrell at Oregon State University found that in growing radishes, carrots and potatoes in a copper azole treated Douglas-fir planter, the copper levels were not higher in roots or tubers of radishes, carrots or potatoes compared to beds constructed from untreated wood. They also state that when people are concerned about the migration of wood preservatives, they can use polyethylene (plastic) to line the inside of the planter. Their scientific results indicate that although plastic lining is “not entirely necessary”, it can be used if there are safety concerns. The use of a plastic barrier will also extend the life of the preserved wood and help keep the raised bed garden soil within the bed area. For proper drainage, the plastic material should not be used underneath the raised bed garden.
Viance recommends for those who have concerns to line only the interior walls with heavy plastic sheeting. There have been no justified claims that today’s treated lumber causes any negative effects from leaching into the soil.
Article updated by Guest Contributor, Edie Kello, former director of marketing for Viance.
Sources
Read the complete study in the article available in the Wood and Fiber Science Journal.
Researchers: It's Safe to Garden with Raised Beds Built with Preserved Wood
Dr. Gerald Presley, Assistant Professor Wood Science and Engineering, Oregon State University