Using Pressure Treated Lumber in Raised Garden Beds

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April 12th, 2009

Short Answer: Yes, it is safe. Long Answer: Read On…

I am a man of science. I don’t believe in anecdotes, and having an analytical mind and having been exposed to rigorous scientific study in college when I was a research assistant in a lab, as well as of course the academic work in college, I’ve always looked at things scientifically, and today I’m going to look at pressure treated lumber.

Many people and sites and magazines will say you shouldn’t use pressure treated lumber, it is bad and will leach dangerous chemicals like arsenic into the soil and it’ll get in your plants and give you cancer.

Okay, there are a lot of assumptions there, and assumptions are bad.

I’m sure we all know the story of fish and mercury right? Mercury gets in the water and the fish drink the water, and since mercury and other heavy metals do not get metabolized, they can permanently build up in fish flesh (this is like lead poisoning in humans). Then predatory fish eat the little fish and they get even more mercury build up. Then humans eat the predatory fish and we get mercury poisoning.

So why can’t the same thing work with plants and treated lumber? Well you have to assume the lumber leaches dangerous quantities of dangerous compounds into the soil, then you have to assume that the leaching travels adequate distance in the soil, then you have to assume that the plant roots take up the compounds and do not metabolize them (remember, plants metabolize many dangerous compounds, house plants clean our homes of dangerous carcinogens) into some other compound. Then you have to assume that the compound is stored in the part of the plant that we eat and at dangerous levels.

There are a lot of assumptions, and just one break in the chain breaks the risk.

CCA lumber contains chromium, copper, and arsenic. Chromium isn’t that toxic and only if we inhale it. Copper isn’t toxic to mammals, and in fact it is used in some skin creams and whatnot. Arsenic is the bad one, a known carcinogen, something to be avoided. Did you know the Romans used to use it as makeup? But people didn’t live long back then anyways.

The truth is arsenic is everywhere, it naturally occurs in soil and water and we eat small amounts of it everyday. The type in CCA wood (inorganic arsenic) is more toxic than the natural types, but just for reference, it is already in the food you grow.

According to this article, which is an excellent source. Studies have been done showing most leaching only occurs during the first rainy season, and that it doesn’t leach more than a few inches from the wood. Then, most plants do not take it up from the soil, the ones that do in only small amounts, and the arsenic is stored in the parts we do not eat. For instance carrots grown in a control bed had 0.05 parts per million arsenic, those in a bed with CCA lumber had 0.11 parts per million, a doubling, but still a very small amount, and carrots were one of the worst (root vegetables in general were the worst since that is where the plants store arsenic).

So, is CCA lumber safe? Well, you can leave it out for one year letting the initial leaching get over. Then you can build your beds and line it with plastic sheeting or roofing fabric or some other membrane to stop leaching, and you can not plant root vegetables in it or near the sides of it where the leaching take place.

All told, by looking at the science, I do not think anyone needs to worry about growing vegetables in CCA lumber beds. Sure, you could use cedar, and pay 8x the price (if you can even find cedar in a 2×10 or 2×12 which is my preferred size), but CCA would be fine.

Should you go out and buy CCA pressure treated lumber to build your raised beds? Well no, you can’t. You see, despite the tiny safety risk, CCA pressure treated lumber was banned for consumer use by the EPA in 2003. Any pressure treated lumber manufactured for consumer use after that date has no arsenic in it. The ban all told was a better safe than sorry issue grown out of kids touching/playing on/eating off of/ CCA playground equipment, not garden contamination, but nevertheless, for the last 5 years pressure treated lumber has not contained arsenic.

So, for those worrying about it, don’t. Save yourself a few hundred dollars and get pressure treated lumber for your raised bed or other garden projects. It is cheaper than cedar, and worry free. Even if it still contained arsenic it’d be pretty safe, but it doesn’t even have that small risk anymore.

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33 Responses to “Using Pressure Treated Lumber in Raised Garden Beds”

  1. Don  Says:
    April 12th, 2009 at 8:33 pm

    Arsenic is no longer used in pressure treated lumber in the US and was outlawed several years ago. Home Depot no longer carries it.

    They use a new process that is perfectly safe to use in raised gardens. Just make sure you don’t use the older pressure treated wood.

  2. John at JWLW  Says:
    April 13th, 2009 at 6:16 am

    Good Morning:

    Whats the new pressure treated wood contain ?
    Does it have a symbol like the “CCA” ?

    John

  3. Mark  Says:
    April 14th, 2009 at 3:23 pm

    The new initials are either ACQ or MCQ.

    ACQ contains no arsenic – only copper and quaternary ammonium compound and has been around now for several years.

    MCQ is a newer treatment that is treated with particles instead of liquid and is supposed to be even more stable than ACQ.

  4. Scotts Soil  Says:
    April 15th, 2009 at 1:09 am

    Pressure treated lumber is a life saver in many situations. I thank god for the scientists that came up with it. Does anyone know how long it lasts? I’m assuming it’s close to a lifetime.. Am I right?

  5. Tiffany  Says:
    April 20th, 2009 at 7:36 pm

    You know, there are quite a few companies who offer safe materials, already treated and ready to go:

    http://www.composters.com/raised-garden-beds.php

  6. gary  Says:
    April 22nd, 2009 at 7:50 am

    Tiffany, sure these companies charge $200 to $600. for their safe materials, pre-fab raised-gardens. If you want more than one, now you’re talking the big bucks.

  7. Jenn  Says:
    April 22nd, 2009 at 9:58 am

    Excellent. This is what I needed to know for my research before I did a raised bed.

    Much thanks.

  8. Annette  Says:
    April 22nd, 2009 at 10:42 am

    PVC? Since when was that environmentally friendly?!?!? It may not leach into your vegetables (What are the long-term studies on PVC filled garden beds?) but then, are you really sure? And PVC is around forever… After all those freezings/thawings, it probably will crack and break. Then it heads to the landfill to live for generations to come…..

  9. Lindsay  Says:
    April 22nd, 2009 at 12:04 pm

    Hi! My name is Lindsay and I run a blog called Frugal and Fabulous. I’m currently running a giveaway for a one year subscription to Flower Magazine. I thought this was something you and your readers might be interested in! :)

    The direct link is here: http://www.frugalandfabulous.org/2009/04/giveaway-subscription-to-flower.html

    Please feel free to enter!

  10. Jon  Says:
    April 23rd, 2009 at 5:30 am

    I work for a window company…I wont say which one..but I will say this…I work in the repair dept. and all of our windows and doors that were milled from lumber treated with arsenic which is pre 1990ish vintage..hold up a lifetime.. all of the rotting window issues are from windows made of lumber that wasn’t treated with arsenic… I understand enviormental concerns..but do you want a 30 thousand dollar window job you did to your home say 10 years ago rot away?…think about it like a homeowner.. P.S. 10yrs?…. no warranty..

  11. Mike H  Says:
    April 25th, 2009 at 7:12 am

    Has it been proven that resins used in wood-like lumber will not leach into the soil?
    Second, is there some simple, soil testing mechanism to monitor leaching from treated lumber ? Can a typical soil test be used ? Would it help to lay treated lumber used for a raised bed on a footing of sand or gravel that could absorb any toxic run-off and prevent seepage spread ?

  12. Carlous Stockton  Says:
    April 25th, 2009 at 9:30 pm

    I Am Building a Raised Bed Garden with 18 old treated lumber from a old deck will it be safe

  13. Joe Patmos  Says:
    April 26th, 2009 at 1:11 pm

    So I finished my raised bed, shoveled in 2 cubic yards of good top soil with peat mixed in and then ran across the pressure treated wood question. I am done freaking out and have been researching the issue of leaching chemicals.

    I am starting to think I may leave it as it and not worry.

  14. Paul Charlesworth  Says:
    April 27th, 2009 at 6:45 am

    Safe is a very interesting word. You could argue that nothing is “Safe.” Everything we do has inherent risks, but I would say that 18 year old lumber has gone through all the leaching it will. Take a look at this Fine Gardening article:

    http://www.finegardening.com/design/articles/pressure-treated-wood-in-beds.aspx

    I just built some raised beds with the new micronized lumber from Ever Guard. I lined them with landscaping fabric mainly because I placed them on the fabric and cut through. This ties the beds to the fabric and stops soil coming out the bottom.

    I think that as people get used to the idea that we most places nolonger use CCA, they will stop saying that PTL is bad for raised beds.

  15. Darren (Green Change)  Says:
    April 27th, 2009 at 6:39 pm

    Thanks for adding some science into this debate. It can be an emotive issue, and people freak out without any concrete information.

    I’ve got some non-arsenic PTL in my vegie beds and have satisfied myself that it’s as safe as any alternative.

  16. Steve  Says:
    April 29th, 2009 at 5:24 pm

    I read this when doing research.

    “Avoid using creosote or pentachlorophenol treated lumber (such as railroad ties) for the frames, to prevent these chemicals from leaching into the soil and injuring your plants.”

    From
    http://www.thegardenhelper.com/bed~const.html

    A different slant on the issue. I’m glad I can use PTL. I have enough left over from deck project to do it with out buying anything.

  17. Mean  Says:
    May 5th, 2009 at 6:42 am

    I just finished building three raised beds with cedar. I used 4by4’s and went 4 high plus a 1by6 mitered top. They look great. They are roughly 8by4, 10by4 and 12by4 feet. Total cost was a little over a thousand dollars. Am I crazy? Maybe. Will they last for 30 years and therefor be the last beds I will ever build? I sure hope so!

  18. Administrator  Says:
    May 5th, 2009 at 7:18 am

    Will you ever grow enough food to justify the cost?

    And I think 30 years is probably a long estimate, cedar is rot resistant, but it is in full contact with soil. I would guess 7-10 years.

    But I’m sure they look pretty.

  19. TF  Says:
    May 10th, 2009 at 12:30 pm

    I just bought pressure treated lumber for my raised beds. I was worried about using it, but its comparative cost to cedar is why I got it. As a precaution, I decided to line the beds with 4ml visqueen plastic around the lumber so the soil won’t come in contact with the lumber at all.

  20. Juli  Says:
    May 18th, 2009 at 12:29 pm

    My husband just built 3 raised beds out of pressure treated lumber purchased from our local Menards. The website we were following said to use cedar and the cost would have been $485. We got all the supplies with the pressure treated for $107. I’m happy with how they turned out and they’ll last a long time.

  21. palexandria  Says:
    June 24th, 2009 at 7:33 am

    Someone asked how long pressure-treated lumber asks. Well, it’s not a lifetime, at least not the stuff in my yard. I just bought this place and there are raised beds in the back yard made with landscaping timbers (round on the sides, flat on top and bottom) that still have their old pressure-treated labels on them. Many of them are rotting. I don’t know how old they are but I’d guess from what I know about the folks who used to live here, they are less than 20 years old. Still, that’s pretty long for something out in weather all the time.

  22. palexandria  Says:
    June 24th, 2009 at 7:44 am

    p.s. Thank you SO much to the person who originally posted this. I was stressing out about all the pressure-treated lumber in my yard, wondering whether I should get my soil tested, thinking I should replace it all and get new dirt, etc… This is great news indeed for me. Especially since I’ve planted all kinds of stuff already including asparagus in these beds. Yippee! I can stop worrying!

  23. Samantha  Says:
    July 8th, 2009 at 4:28 pm

    I was worried because I am putting up a fence made from PTL and it is right next to my garden. Thanks to the original poster I don’t think I’ll sweat it. Some people have brought up lining their gardens with plastic to prevent leaching from the PTL. Hmmm, what with all the news about bisphenols in our plastic, one wonders if plastic is safe..

  24. John White  Says:
    October 10th, 2009 at 5:02 am

    Palexandra noted that her “pressure treated” landscape timbers were rotting.

    Most landscape timbers sold at the big box stores, they are typically 4×4 or 5×5, are dip treated not pressure treated, but unless you read the fine print on signs or the labels you would probably presume they were pressure treated because they look identical to pressure treated.

    Dip treated wood has only a thin surface layer of treated wood, the cores and any cut off ends are untreated and will rot like ordinary wood. Of course dip treating is less expensive than pressure treating, and this is a clear case of getting what you pay for.

    John White

  25. Bruce, Austin, TX  Says:
    November 4th, 2009 at 4:24 pm

    Is “dip treated” landscape timbers more or less likely to leach arsenic? And for those who would like to be sure, where and how would you get a soil test to check arsenic levels?
    Thanks

  26. Frank  Says:
    January 8th, 2010 at 6:30 am

    I built a raised bed, vegetable garden using the 8′ pressure treat yawn post sold at Lowes. I was concerned about any chemicals going into the soil around the post. I lined it with a heavy plastic. Should this help with preventing chemicals from entering the ground?

  27. Pamela Cohen  Says:
    February 21st, 2010 at 11:15 am

    I think most of us have enough toxins in our ‘body bank’. At Gardenaut I read a response as to what to build raised beds out of, which is regular lumber, because in ten years, you might want to change the design of your yard, anyway. Why worry or rationalize? After using redwood from an old water tower to build two raised beds last year, I used a linseed oil that had carcinogens added to it. Thinking I could keep it from leaching into my soil, I used that black road fabric, and thought about using the black landscape fabric, but then I wasn’t sure about black AZO dyes that also cause cancer, or what leaches out of plastic. Babies today are born with over 200 foreign, toxic chemicals in their bloodstream.
    I would rather use rock, as it holds the heat and extends the growing time of plants. I think dry stacking or single stacking would be best, as I’m not sure I want the lime from cement binding elements in the soil, either.
    Now, if the galvanized mesh at the bottom of the gardens (to keep the moles from destroying my efforts) won’t kill me off sooner, I can stop worrying. What a conundrum of thought.

  28. Administrator  Says:
    February 23rd, 2010 at 6:03 am

    I’d rather use stone too.

    But it is exponentially more expensive than wood, and if I’m growing my own food to save money, where is the savings then?

  29. mike  Says:
    May 15th, 2010 at 3:53 pm

    can I use pine 2×10 and stain it?

  30. Administrator  Says:
    May 16th, 2010 at 8:15 am

    You can, but you shouldn’t.

    1. Stains are probably not healthy for the soil.

    2. Stains, sealers, etc, meant for decking, is meant to protect the wood from water than falls and runs off. They will not stand up to being in constant contact with soil. They will rot quickly.

    You either need to use pressure treated wood, or a rot resistant (and expensive) species like teak, cedar, cypress, or redwood.

  31. Theresa Gallo  Says:
    May 24th, 2010 at 7:15 am

    Hi,
    Also a person of science–well, a reasonable math PhD, I certainly wouldn’t risk it. I’m planning on using untreated wood only. If I have to replace it in a year or two so be it. I might just spend the extra money for naturally rot resistant sustainably harvested wood too. My toddler will be with me playing in the dirt, planting and watering. She’ll eat the food we grow. She certainly doesn’t need arsenic exposure. I know we’re all exposed to toxins daily, but I won’t knowingly subject myself and my family to toxins. The Environmental Working Group was key in getting the arsenic outlawed in treated wood.
    Here’s the EWG info page…check out their risk assessment.
    http://www.ewg.org/featured/232
    Enjoy your (hopefully non toxic) gardens!
    T

  32. Administrator  Says:
    May 24th, 2010 at 8:00 am

    I’m not sure which part of your scientific mind fears something that hasn’t existed in 7 years. It sounds more like superstition than science to me.

    Any pressure treated wood you buy today has no arsenic.

  33. John Saltenberger  Says:
    June 15th, 2010 at 10:58 am

    Here’s a quote from the Environmental Working Group article cited by Theresa Gallo above:

    On February 12, 2002, under pressure by consumers, members of congress and the EPA, the wood industry agreed to stop using arsenic-based wood preservatives as of December 2003. By 2006, US consumption of arsenic had dropped more than 300 percent.

    So, that article echos the original author’s claim: Pressure treated lumber sold in the US after 2003 contains no arsenic. It would seem that risk of arsenic exposure from using pressure treated lumber is no greater than background.

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