Treated Lumber in Your Garden: Is it safe?

Treated Lumber in Your Garden: Is it safe?

  • CCA
  • cedar
  • garden
  • gardening
  • lumber
  • pressure
  • PT
  • treated

With an ever-growing community of gardeners, we often get a question at Sunbury Cedar that goes something like this: can I use this pressure treated stuff for my garden bed? Is it safe? Will my family get sick?

It’s an important question, and one that I’ll answer in this article. We’ll first look at the history and processes involved with pressure treated lumber, the chemistry behind cedar and finally discuss the pros and cons so that you can make an informed decision.

So what is pressure treated (PT) lumber?


It’s exactly what it sounds like. Typically, mills take a cheaper stock that is prone to fungal decay and soak it in a chemical bath while applying pressure. This process forces the chemical into the wood, increasing the decay-resistance of the wood significantly.

In the past, a chemical known as chromated copper arsenic (CCA) was used in almost all PT lumber. Now one of those chemical names may jump out at you, namely arsenic. Yes, arsenic is poisonous to humans. Once the general public realized this, there was a movement to stop using the chemical altogether. The wood products industry voluntarily stopped using CCA in residential lumber in 2004, though it is still widely used for telephone poles and in other structural applications. It should be noted, that there are no confirmed cases of families or children becoming sick after being in contact with CCA lumber. The levels of arsenic in CCA lumber were such that you would have to consume a large amount of wood fibre to see an immediate adverse reaction. I do not in any way recommend this, but you get the point. Additionally, some researchers have proposed that plants would not survive long enough to uptake enough arsenic to affect long term human health.

Regardless, CCA lumber is not produced anymore, so we don’t have to worry about it. Since 2004, a variety of new treatments have been developed to preserve lumber. Although there is limited research on possible health side effects of these new treatments, most manufacturers provide extensive warnings regarding their use in gardens.

With all this said, I don’t want to scare anybody off the use of PT lumber. Modern pressure treated lumber is a safe, quality product when used correctly.

A more popular alternative to PT lumber in gardens is red or yellow cedar.


Red cedar contains an organic compound called Thujaplicin. Yellow cedar contains several extractives that contribute to its durability, chief among them being the compound Nootkatin. Both of these compounds exhibit anti-fungal and anti-bacterial properties that make cedar a naturally durable material. Yellow cedar is considered more durable, as it is significantly more dense and harder than red cedar. The natural extractives found in cedars provide them with excellent durability overall, allowing them to survive for well over 10 years when in contact with soil and moisture, and in some cases over 100 years. Keep in mind, however, that wood is a natural material, and because of this its properties are inherently variable. There is by no means a guarantee on how long a particular board will last in your garden.

To answer the questions, we started with: you probably shouldn’t use PT lumber in a garden that’s growing food for you or your family. If it’s a garden that was built before 2004, you should definitely replace the PT lumber, as it was likely treated with CCA. Even if it isn’t part of a food-producing garden bed, the arsenic in the treatment can affect water supplies. Don’t be afraid to use PT lumber in your backyard, but use natural products like red and yellow cedar for your vegetable gardens.

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