Using Pressure Treated Lumber in Raised Garden Beds

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.

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

  1. susan  Says:

    This is information on an actual study done at Ohio state university on using pressure treated wood with raised garden beds.

  2. Chris  Says:

    Contrary to your statement in the second paragraph, the little fish do not “drink” the water and intake the Mercury in that manner. The dominant route for Mercury into the food supply is through bioaccumulation. Small amounts of mercury are taken up by plants, those plants are eaten by small herbivores which are in turn eaten in greater quantities by others up the food chain. The farther up the food chain, the more Mercury “accumulates”. Raised beds cannot be compared to fish and Mercury, because bioaccumulation is not an issue in raised beds.

  3. Karen  Says:

    Thanks to this forum I now don’t feel compelled to replace the soil in my new SFG. I followed the directions in Mel’s book and went to several Home Depot stores asking for wood lath for the grid. I was adamant the it not be treated since I was using organic soil components and plants. Only one store said they had some, which I had cut and placed in my garden. Over a week later, I read on the tag on the wood “PROSEAL LATTICE TRIM”. So, nobody had untreated wood, but one store sold me stuff that they said was untreated. I wonder where Mel Bartholomew gets his supplies.

    Regarding the cost for raised beds, mine were $40 each from Wegman’s for a kit of cedar pieces that are supposed to slide together and make a 4′ x 4′ x 6″ bed. They all required some pounding together or sanding, and some of the corners split, but I’m happy with the price. They can also be stacked for growing deep-rooted crops.

    Regarding the Eco wood treatment, beware that it immediately turns your nice new looking wood into an aged-looking greenish gray color. Some folks seem to like that. I hate it. I only used it on my first bed and stopped as soon as I saw what it did to my beautiful new planks.

  4. JoeBob  Says:

    Thanks for the informative article. There are enough chemicals in processed foods to be concerned about without stressing over homegrown veggies-it’s nice to be able to put this issue to “bed”. Plus, Stephanie nailed it–stress kills. Chill out, enjoy the fresh fruits of your labor and take in a little vitamin D the way nature intended-get some sun.

  5. David  Says:

    ACQ and MCQ contain large amounts of copper. Copper has a very low oxidation rate which will cause fasteners to rust much faster than they would if nailed or screwed into plain lumber. Becasue you’re going to water the garden a large amount of free oxigen will be available and fasteners will rust very fast. To avoid this you can use Stainless, Hot Dipped galvanized or larger (1/2 inch diameter) fasteners. Enjoy you gardening.

  6. Mike  Says:

    I get about 7 years out of 2×10 plain spruce. I just put in some more beds and brushed linseed oil on them.

  7. Michelle  Says:

    Thank you for the info. I have some wood left over from the deck we just built. I thought it would be a good size for planters, but someone told me they didn’t think I should use it. Glad I can reuse it and save a fortune!

  8. Matt  Says:

    Susan- thanks for that link, that’s great info. I would choose against using CCA wood (any more than I already have) in a garden based on that info. CCA is no longer widely used in the USA and Europe but still seems to be the dominant form here in NZ. As much as we like to market ourselves as “clean and green” we’re a bit behind the curve on some things! We have a powerful timber industry here – read into that what you may.

    Re-using old deck wood would probably be OK as much of the leaching may have already occurred. Do try to catch as much of the sawdust as possible – cut over a tarp on a non-windy day and bag and dispose of waste. Carpenters working on our house cut a bunch over the lawn and we couldn’t get grass to grow there for two years. That should tell you something about how “benign” it is. I think anyone lining PT gardens with plastic is probably just making things worse as we are starting to learn about how harmful plastic leaching is.

  9. Rick  Says:

    I’m thinking that some people are just afraid of everything. I appreciate the original poster’s efforts to educate us on this issue – and the science behind it. I do not live in a bubble. In a gardening class I took, a woman going over 300 lbs was going on and on over the health risks of inorganic vegetables. Really??? I am supposed to take m health advice from you? My great grampa lived to 91 as a farmer…and used methods that would make you pucker. Make your own choices. Thank you OP!

  10. Hank  Says:

    WOW…! I am so glad I found this discussion concerning PTL … 99% of the comments were quite helpful. I am residing in Galveston, Texas and was wondering about the toxicities of PTL, and whether they were safe to use or not. I’m planning on building two or three raised-beds using 2×12’s PTL. I’ll probably make my beds 8ft. x 3ft. Thanks for all the comments. I am not afraid of using the newer PTL’s since it has been ten years since the aresenic ban began in 2003…and it is now 2013. Thanks All!

  11. Mark  Says:

    It’s outright irresponsible to write a blog stating pressure treated wood is perfectly safe, when you don’t even know what the contents of it are (and more over, make obvious errors).

    To use this in your garden, where you grow food, is just one of the stupidest things I’ve ever heard of in my life. Spend the extra $2 on Cedar; BTW, here it’s actually nearly the same price.

  12. Doldrums  Says:

    This article is disappointing. The writer claims to be a person of science who worked in a lab. Wy then not conduct your own experiments regarding leaching instead of relying ona literature review that at best rely on received wisdom which are inaccurate to begin with. Why would you risk leaching in the first place. The whole point of home gardening is to take back your own control of your food supply and to try and minimize as much your foods exposure to industrial processes and chemicals. PTL is just that. Untreated Pine works great. It may rot in 5-6 years but by then the boards are easy to replace.

  13. Administrator  Says:

    Uhh why not do my own study? Because I don’t own the necessary lab equipment, or have the time. I’ll have to take the word of people who did do the studies, because I believe them, not some vague industrial luddite boogeyman. You might as well ask why I don’t do my own crash tests prior to buying a new automobile. It isn’t really practical, you know?

  14. Administrator  Says:

    Oh Mark, yes, it is safe.

    Some people get a little too overzealous on environmental issues. Not everything man made is bad, not everything natural is good. If you ever take a chemistry class you’ll learn everything is a chemical, and just because something is sythentic vs natural doesn’t make it any less or more a chemical or less or more dangerous (nevermind that the ingredients in pressure treated lumber are all naturally occuring). Plus, as I explained above, you make a ton of assumptions assuming that something nearby the soil in which you grow food crops is going to end up on your plate.

  15. PinkinTN  Says:

    Individual choice, but why even risk it? I just made 3 beds from cedar fencing bought from Lowes for less than $2 ea. Each bed measures 3’x 6’x 12″ = $12 ea. Will I have to replace these beds every 2,3,4 years? yes, I will but with peace of mind that my family is not “ingesting or not” wood treatment leaching into the soil. To me that peace of mind for $36 is cheaper than that chance of future medical bills and meds because treated lumber lasts longer. Agree or not, your choice and my opinion.

  16. Jon  Says:

    Great article. I just left Home Depot where I was comparing prices to build raised beds. I decided to do a little reading before purchasing because I had heard the stuff about pressure treated lumber. I now plan on going with PTL, as it is the cheapest and longest lasting. To all those who say, “why even take the chance?”, I say how do you even live your life? How do you cross a street, drive a car, fly in a plane? Why even take the chance? Take this philosophy to it’s logical conclusion and you end up living in a bunker eating organic granola and water.

  17. Chris Welzel  Says:

    I am doing more research on the Australian methods of treating wood but I noticed all the holier than thou comments on using cedar. A quick search shows that cedar has the following traits. “It is common for the dust to cause dermatitis, asthma, nasal cancer, nose bleeds, giddiness, rhinitis and stomach pains.” I guess all the know it all experts didn’t research the ‘safe’timber.

  18. Dave from MA  Says:

    To PT or not to PT, that is the question. The studies on old Arsenic treated indicate very very low concentrations at even optimal leaching conditions; ie the wood was powdered. Copper Azole (CA-B) retains even better. Melted food grade canning wax and brushed the inside of the box with a nice fat waxy coat mostly for water resistance and durability, but works better than plastic if that’s what it takes to dispel the alarmism……

  19. Don L  Says:

    I came to this site because I found out that a local composting facility is grinding up PT wood along with everything else and then marketing the finished compost to gardeners. I’m glad that I go through the process of making my own compost and not buy commercial compost.

  20. Shannon  Says:

    I have a question. What about using 20 year old pressure treated wood in a garden bed? Would it be safe to use for a long period of time? I can only assume that nearly all the chemical it was used to be treated with would have leeched out by now. However since I want to make this bed part of the garden and possible grow herbs, I want to make certain it is safe. Would it be? Or would it be better off as a one time use?

  21. Administrator  Says:

    @Shannon – should be okay. If you like you could avoid planting root veggies in that specific bed, but as you say, most of it should be leached out, and even if it wasn’t, there possibility of transmission is so ultra low.

  22. Lindsay  Says:

    One thing I found is 5 year old pressure treated fence posts totally rotted due to water rot. The type of wood used in this PT process seem to be quite soft. Therefore other treatment to prevent water adsorption may be a good idea for subterranean use.

  23. Brittney  Says:

    I have been doing so much research and when I found this article I was excited that I didn’t have to take apart the huge box garden I made but reading the comments made me worry again…

    I researched my local store I buy my treated wood from and found the company who makes the treated wood((it will say on the tag at the ends of your wood or online))…

    **Ecolife** is the company that treated my wood, infact they treat almost all wood st Lowes… which says they follow the AWAS standards but I decided to read their “safety” list AND THIS IS WHAT I FOUND AMONG MANY OTHER CRAZY WARNINGS….

    **** “Do not use pressure-treated wood in circumstances where the preservative may become a component of food, animal feed or beehives.”**** so even though they follow the standards given that says it’s safe, their own website says DO NOT USE AROUND FOOD, ANIMALS, BEEHIVES….

    Just wanted to post this here for others who were looking just like I was. If you want to see this information for yourself, go to GOOGLE and type in ECOLIFE TRESTED WOOD ((the website http: looks like or such)) and then click on “safety” towards the bottom

  24. Administrator  Says:

    In our litigious society warnings often go above and beyond, but on the plain words of it they are saying “Don’t eat our wood.” Which is probably good advice. They’re not saying it is going to get into your food if grown in proximity, they’re saying, don’t eat the actual wood. You should also not breath the dust in when sawing it, as all carpenters know, and never burn pressure treated wood either. It is however safe to use to hold up dirt in a raised bed, just keep your feasting to the vegetables inside, and don’t eat the raised bed itself 😉

  25. Red T  Says:

    I came here (new to gardening) to find out the longevity of Douglas Fir used in raised bed gardening, and learned much more! Though I still don’t know how long to expect the Douglas fir to last in my raised beds here in the desert.

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