Pressure Treated Lumber in Your Garden
Many of our clients ask about raised gardens but have concerns about the use of pressure treated lumber around them. 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 concerned you. Therefore, is pressure treated wood safe for the garden? The short answer, Yes!
History of Pressure Treated Lumber
To understand where the concern is coming from and what dangers may be involved, we first need to understand a little history about treated wood. Wood naturally breaks down and rots in time. Fungi and insects commonly found in a garden setting also contribute to lumber degrading. Scientists have long been trying to make wood more durable.
First, creosote was used to treat wood. It’s 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 from insects and fungus, but it also kills plants that are close to it. Also, it was recently proven that it is a carcinogen and harmful to humans.
Chromated Copper Arsenate (1930 – 2003)
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 1940’s. Chromium, Copper, and 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 began 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 they were going to use wood treated with CCA in a garden to plant vegetables 12” away from the wood. A much bigger concern was for people handling the wood.
Alkaline Copper Quaternary (Used Today)
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 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.
Not everyone is satisfied using pressure treated wood in the garden. Untreated wood is readily available, and some wood like cedar, is naturally more durable. The Canadian Department of Agriculture 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.
LCM General Contractor
LCM General Contractor can build you a beautiful, raised garden bed 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 pests. 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.