Is Pressure Treated Lumber Safe?

Is pressure treated lumber safe to use in applications like garden beds, compost stations, and chicken coops.

It depends on who you ask.

Although it had been sold for decades for use in outdoor construction and garden projects,  lumber treated with Chromated Copper Arsenate (CCA) was banned for residential use  in  2003 because of concern that arsenic could leach into nearby soil and contaminate plants and people.

The two new compounds that have replaced CCA  - Alkaline Copper Quat (ACQ) and Copper Azole (CA-B) - are free of arsenic, and rely on an increased percentage of copper to protect wood from insects. Quat, the fungicide in ACQ lumber that prevents soil fungus from attacking the wood, is also used in disinfectants and swimming pool chemicals.

CA-B treated lumber uses tebuconazole to protect wood from soil fungus, which is also used as a fungicide on food crops.

Scientific studies have shown that while copper from ACQ and CA-B lumber does leach into soil, it's limited to only a few inches around the site of contact, and levels are so low that risk to humans from exposure to copper is tiny.

So with all of this evidence that treated lumber is safe, why is it still frowned upon by the organic gardening community?

Perhaps folks are uneasy about chemicals with names like tebuconazole coming in contact with their food, no matter how small the amount or how many scientists say it’s no big deal.

It says something that, on its own website,  Wolmanized Outdoor – one of the largest manufacturers of pressure treated lumber -  does not recommend using pressure treated wood where the chemicals may become a component of food, instead suggesting that a liner be placed between the wood and soil where edible plants are grown.

But the effectiveness of a liner to separate soil and treated wood is iffy at best, and certainly not reliable for a long period of time.

Garden forums and blogs are full of DIY’ers assuring each other of the safety of their treated wood beds and coops, and lamenting the cost of naturally rot resistant woods like cedar, redwood and cypress -  in one case describing cedar  as “8x the cost of pressure treated wood”

We’ve found that premium Western Red Cedar lumber from the local lumber store to be about 3x the cost of pressure treated wood, which might be a difference of couple hundred dollars for most garden projects.

We’ve also found cedar to be 1000 times better looking than pressure treated lumber in our garden projects and because it’s completely free of synthetic chemicals of any kind, our customers can focus on enjoying their garden instead of wondering if the wood is safe.

So back to the original question: Is treated wood safe?

In the grand scheme of things there are probably other chemicals that are more toxic and cause for concern than ACQ and BA-C, and if you built a raised bed or coop with treated lumber, you probably don’t need to rush out and update your will.

But for what it’s worth, pressure treated lumber is not allowed for use in certified organic food production... which is why we choose cedar instead of pressure treated lumber for our garden projects.

Comments

[Andrew Thiessen]

Here, here Matt! We too use only cedar for veggie beds. I met w/ Selwyn Elementary this morning discussing just this issue.

I also use untreated cedar to build my honey bee hives because I originally felt scraping and painting pine hives sounded like the kind of fun I'd rather not indulge in! Plus, cedar hives look great once they weather to a natural grey after a season.

Keep up the good work!