Raised Gardens and Pressure Treated Lumber
Many of our clients ask about raised gardens but have concerns about pressure treated lumber. If the raised garden is built with it, will it be safe for growing vegetables their families may eat? You may have heard stories that made you concerned. So, is pressure treated wood safe for the garden? The answer may surprise you.
History of Pressure Treated Wood
To understand Where the concern is coming from and what dangers may be involved in 2022, we first need to know a little history surrounding treated wood. Naturally, wood breaks down and rots over time. Fungi and insects commonly found in a garden setting also contribute to lumber having a shorter life span. Scientists have been trying to make wood last longer for a long time.
One solution was to treat wood with creosote, that black smelly liquid you may have seen leaking from an old telephone pole or a railway tie on a hot day. Creosote works well to protect wood, but it also was found to kill any plants close to a creosote treated log. Another negative thing about creosote only recently discovered, is that it is a carcinogen and harmful to humans.
Chromated Copper Arsenate (CCA)
In the 1930’s chemists came up with a new chemical to protect wood. Chromated Copper Arsenate (CCA) was used to treat wood beginning in the 40’s. Chromium, Copper, Arsenic, the main chemicals involved, together were very effective in protecting wood and it has been used in residential settings for most of the 20th century. People started asking questions about CCA’s potential to harm the environment if broken down and released. Most of the concern was related to the chromium and arsenic components. Many studies showed that even if these chemicals leached from the wood, they would only travel a few inches into the surrounding soil. Therefore, people were told if used for planters to, as a precaution, plant vegetables 12” away from the CCA treated wood. A much bigger concern was for people handling the wood.
Alkaline Copper Quaternary (ACQ)
In 2002, the Environmental Protection Agency (EPA) and the Wood Preserving Association (WPA) Decided to stop the production of CCA treated wood. Since 2003 CCA treated wood is impossible to buy and use in a residential setting. Today, (since 2003) Alkaline Copper Quaternary (ACQ) is most commonly used to pressure treat wood. It is universally recognised as being safe for gardens and residential settings. It’s primary ingredient copper, is naturally occurring in the soil and is an element that both plants and humans need.
Organic Plants and Treated Wood
Not everyone will be happy with using pressure treated wood in the garden. Untreated wood is readily available, and some wood, like cedar, is naturally more durable. Agriculture and Agri-Food Canada does not allow certified organic growers to use pressure treated wood in their gardens. Obviously, they still believe some chemicals could still infect nearby plants. If you like the benefits of pressure treated wood but want your garden to be more organic, consider lining the beds with plastic and create a barrier between the wood and the soil.
B.R.A.G. Contracting Inc.
B.R.A.G. Contracting Inc. can build you beautiful, raised garden beds from pressure treated or non-treated wood. Our clients have had raised gardens built for a few good reasons. Having a raised garden protects your plants from rabbits and other invaders. If you’re older, a raised garden reduces the pain of bending over or kneeling for prolonged periods. And they make beautiful features and barriers when included in decks. Ask us about including raised beds in your deck design.