Is it safe to use treated wood for raised bed gardens?

Marjory Wildcraft

The answer to that question used to be a solid "no", but I recently came across this post by The Natural Handyman who says the old chemicals used before are not in use now. And it's safe to use pressure treated lumber.

The Natural Handyman says: until 2003, the most common preservative used for pressure treated wood was chromated copper arsenate (CCA), a compound using arsenic as its primary rot protectant. Over years, the industry, in cooperation with government recommendations, phased out the use of CCA for all residential and most commercial wood pressure treatment. Part of the reason was the fear that the arsenic would poison the soil and anyone who touched it. Though actual cases of poisoning via pressure treated wood use by the public were hard to find, there was enough circumstantial evidence of soil contamination to warrant a change.

Here is the rest of the post:

https://www.naturalhandyman.com/iip/infxtra/infptforraisedgardens.html

Torey

There is still a lot of that CCA wood out there in use on decks, fences, gazebos and other projects. This wood is extremely dangerous when burned. Firefighters (at least in my area) have been cautioned about exposure when attending fires that may contain large amounts of CCA treated wood. High concentrations of arsenic can be found in the ash. So, please don't burn any CCA treated wood. Mark it and send to a hazardous materials waste site. If you have to cut this wood for any reason, make sure you are wearing proper PPE.

This is a link to the SDS sheet for CCA. https://www.koppersperformancechemicals.com/sds/pdf/cca-sds-english.pdf

This is a link to a case study of a family who suffered with extremes symptoms of arsenic poisoning from using CCA scrap wood as a heating source. https://www.nap.edu/read/4795/chapter/14

This is a link to an article that states 1 Tbsp of ash from CCA treated wood is enough to be lethal to humans. http://www.noccawood.ca/docs/cca_wood_ash.html

If you are buying newer, pressure treated wood, check to see which preservative type products have been used in the manufacturing process. Some pressure treated wood is being treated with pesticides (to reduce damage by insects) and herbicides (to reduce damage by invasive weeds). I don't think we want either of those in our food gardens if we are growing organically. Caveat emptor!

Lisa K

I think I will stick to untreated cedar or redwood even if I have to replace them every few years. But yet cinder blocks.

Wendy

I use untreated wood, and yes, they need to be replaced every 5 years or so. I don't like having to guess what is in the wood and if it might be leaking into my soil.

gardneto76

I have always used untreated wood, then applying linseed oil to the outside of the bed after it is built. This is to help protect it from the intense sun here in Phoenix. I built a compost bin and it has lasted several years. I forgot to treat the boards that separate the bins and they will need to be replaced this year, but the outside is doing amazing still 5+ years later.

Carlos Clavell

Thank you for the heads up on the treated wood board. I will have to exchange the wood for a more organic friendlier version. Home Depot store say on their website to line the wood with a plastic when using it for edible plant garden or use natural fir/cedar untreated wood. I wish I would have known this prior to making the purchase but at least I didn't implemented the wood board. Thanks again guys!!

Brindy

Thank you for the article. I'm thinking I still feel safer with untreated wood, but @Lisa K mentioned cinder blocks. Would those be safe?

Torey

Cinder blocks and concrete blocks are two different products. Cinder blocks are made with by products of coal burning, mixed with Portland cement. Concrete blocks are made with aggregates (sand & gravel) mixed with Portland cement. Cinder blocks are cheaper and lighter. But they aren't always labelled as to what is in them.

This is an article that discusses the controversy about using them in garden beds. Plastic is suggested as a liner for any raised bed construction material that may have been treated or have chemicals that might leach, but I don't like that idea either.

https://buffalo-niagaragardening.com/2015/09/29/are-cinder-blocks-ok-for-vegetable-gardens-answers-to-that-other-soil-safety-questions/

I prefer to use wood for my raised beds and just replace it as necessary. It will last longer if it has some sort of oil treatment on the outside. Rocks work, too. I use rocks on the outside of the garden when I am building beds by the house or at the edge of the driveway.

VermontCathy

My cold frames are 7 years old, and while they have been starting to rot out for the past year or two, I didn't feel the need to replace them until this year. I'm about 75% done with the rebuild.

Fortunately the lids last longer than the part that touches the ground, because lids are much harder to build.

vickeym

We have 10 acres so there is always dead fall trees around. That is what I usually use for my raised beds. They will rot out after several years, but they last well enough for me. Since I have them available and they are free, they work well for me. Also, my husband has a chain saw mill and when he cuts slabs off the outside of a log he is making lumber from, I often use them as well. I know this won't work for everyone. But has been a huge help and a way to use up wood that is not fit to build with otherwise.

water2world

Lots of good info--getting reading to prepare for raised beds!

https://community.thegrownetwork.com/discussion/comment/902011#Comment_902011

Should be able to find this!

ChrisHaukoos

https://community.thegrownetwork.com/discussion/comment/901956#Comment_901956

Thanks, Torey!!! Wow, long answer, but definitely good information and very helpful too.

Marjory Wildcraft

https://community.thegrownetwork.com/discussion/comment/911578#Comment_911578

Yes @torey is awesome.

matt251

Pressure treated wood used to contain arsenic as the wood would be soaked in it to kill bugs, parasites etc. However, that practice has been banned since 2003, at least here in Canada where I live it has. But, I'm pretty sure the U.S. banned it as well, but don't quote me on that.

LaurieLovesLearning

Welcome @matt251! Please leave a short intro in our introductions so we can know what part of Canada you are from. 😄

https://community.thegrownetwork.com/categories/introductions

You'll be able to find FAQ & tutorials in "Our Front Porch" if you ever need them.

A person should still be aware that there are still chemicals in some new treated wood that are most likely best avoided by any food areas. Last year, we came across a pile of new treated wood by a tower in a provincial park that had chemical warning labels attached to them.

It still remains wise to know what your wood of choice has so that you are aware of what will be going into your soil & food. It could easily be just like the BPA mess. They may take one away & replace it with another just as harmful or worse. Somehow, the truth tends to come out later rather than right away.

Edit to add: According to this company in BC, it is still used in some situations. It isn't used in playgrounds & residentially, but can still be present in industrial & agricultural use (fenceposts are one).

https://www.pwppost.com/process

Here's more on the various treatments and some of their safety issues:

https://www.bobvila.com/articles/7-important-things-to-know-about-pressure-treated-wood/

Torey

Hi @matt251. Welcome from another Canadian.

You are right about the arsenic but even though it has been banned you might still find it as @LaurieLovesLearning has point out. However, there is old wood that is still in use in decks and other household projects. If you are tearing down an old deck or other structure with old CCA, you have to be careful with it.

jowitt.europe

We use untreated larch wood boards. At least 3 cm thick. They keep very long. It is considered to be the best hard wood. I would expect that our high beds will last at least 10 years. We buy boards from a local company. It is easy for us, as larches grow everywhere where we live.

Lisa K

Big Lots had some for sale that were stainless steel, which reminded me about using water troughs for horses.

Cornelius

What about galvanized steel beds? I know a company in Australia makes them and are used by one of my favorite YouTubers (Self-Sufficient Me).

Lisa K

@Cornelius I went and looked at the Big Lots catalog again and they are galvanized not stainless steel.

MissPatricia

I used concrete blocks. Two high makes it possible to sit and rise easily. The big problem is that they are very heavy for this small, older woman.