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Re: Use of treated lumber not recommended for vegetable rais ed beds

  • Subject: Re: [cg] Use of treated lumber not recommended for vegetable rais ed beds
  • From: Dboek@aol.com
  • Date: Mon, 31 Dec 2001 22:10:04 EST

Hi, and happy New Year everyone,

I'll add my 2 cents on top of Gwenn's. 

Treated lumber is not by any means the only way to hold soil in raised beds. 
The easiest way, of course, is simply to mound up the soil, as Alan Chadwick 
taught decades ago, and as traditional gardeners around the world have done 
since time immemorial. 

Treated lumber is an easy and familiar material that seems 'convenient'. You 
(or eager donors) can buy it in a big box store, cut it with power tools, 
make something that looks 'nice' (if you like square corners). Other than 
that, there is no reason whatsoever to use it. And once you've got it, you 
can only get rid of it by hauling it to a landfill for toxic waste.

Lots of people have used it, as Gwenn has, innocently enough. But that's no 
reason to continue to use it.

The risk from leaching is real and documented (you've tested soil, 
Gwenn-thanks for sharing your data. However, what about your root vegetables 
growing within a foot of the edge of the wood?). But leaching is only one of 
the problems with CCA wood. (The A represents 'arsenic', by the way, the most 
dangerous poison in the wood, the two Cs are for copper and chromium.)

CCA lumber is made from cheap pine, grown non-sustainably in monocultural 
plantations, many of them in the rural South of the USA. The negative 
environmental impacts of these huge 'tree farms' are enormous. 

The heavy metals are forced into the wood under tremendous heat and pressure, 
using a process that is supposed to make them bond permanently with the wood. 
No doubt about what they do - they are poisonous metals, pure and simple, 
that will never break down biologically. A termite eats them, it's a goner. 
The same, potentially, is true for any organism, including me and you.

The biggest risk to people, probably, is from two risk factors, neither 
having to do with eating. First, when you saw the wood, the sawdust is 
extremely hazardous. You are supposed to wear a mask and gloves and be very 
careful about working with CCA. Over and over, though, I've seen people 
ignore precautions. If you do your cutting in the garden, the sawdust - small 
particles that can free the toxins - can very easily end up in a garden bed. 
Also, you can pick up some toxic metals by touching the surface of CCA. Just 
watch children carefully, don't let them touch the sides of the beds when 
they are weeding... (that's the reason it is not used on playgrounds in NC - 
though people here ignore the research and common sense and still use it. - 
It's cheap and everybody does it is the most common explanation). In 
addition, if you burn it, the fumes are very dangerous.

As the wood weathers and decays (CCA prevents insect damage and fungal rots, 
not weakening from weathering and physical stresses), the wood fibers began 
to fall apart, and sooner or later you have a concentrated pile of high 
arsenic material in your garden. As Gwenn rightly points out, our cities are 
already highly toxified environments, thanks to our past behavior. Using CCA 
lumber does nothing to help correct this problem, however, it only makes it 

The kicker with CCA is that once you've got it, you are stuck. You can only 
dispose of it in a toxic landfill, in most states - and leaching may already 
have moved toxic metals into your soil under the wood, as Gwenn found. The 
plastic liner idea, though a creative notion, really doesn't solve this 

I agree with Gwenn that plastic 'woods' are currently very expensive and hard 
to find - as well as very heavy. My suggestion is to use recycled materials 
instead, especially concrete, rock and pavement chunks. At Berkeley's Edible 
Schoolyard, I saw how the children and gardener David Hawkins made lovely 
beds and even a high retaining bank using chucks of debris from an old 
parking lot. You can also mix inexpensive concrete with soil to create 
earthen blocks. Not only is this free, but you set a good example of 
recycling in action. Bonus - you are not tied into strictly rectangular 
patterns for the garden beds. Mighty nice in Squaresville.

Locally, I'm using a lot of rock. A nearby quarry sells rock cheap, $12 a 
ton. I pick out nice pieces of blockish riprap and drystack it. True, this is 
for a home garden and not all community gardens will want to do this. But it 
works nicely. Think locally.

Last of all, the most important thing is to get people gardening. I have 
strong opinions about CCA (comes from a background in sustainable agriculture 
development, I reckon), but I deeply respect the fact that Gwenn and her 
gardeners are doing soil testing and making up their own minds. As much as I 
dislike CCA, there are plenty of other things that are much more dangerous to 
people, especially in the inner city. The essential thing is that they are 
enabling people to garden and think for themselves. In 2002, that's my wish 
for everyone.

Don Boekelheide
Charlotte, NC

In a message dated 12/31/01 3:55:15 PM Eastern Standard Time, 
Gwenne.Hayes-Stewart@mobot.org writes:

> Thought we'd put in our two cents here at Gateway Greening, St. Louis.  We
>  use pressure treated lumber for our raised beds and have done so for 
>  years.  Common sense would tell you that this is not a good idea.  However,
>  every couple years, we test the soil in the beds, old beds, new beds,
>  middle, ends, sides, and the soil outside the raised beds. 
>  In every case, in every series of tests, we discovered NO leaching inside
>  the beds.  There were minute traces directly underneath the timbers in one
>  test.  The soil outside the beds was determined to be unfit for food
>  production for more chemicals than one could count.
>  Like many of you, our gardens are on abandoned lots in the inner city core,
>  with buildings collapsed into their foundations with a skin of top soil
>  covering heaven knows what.  
>  Recycled plastic lumber costs too dang much money. We will continue to test
>  and will stop using treated lumber if we ever detect leaching into beds.  
>  far, it just isnt there.
>  I read somewhere that some folks line the timbers with plastic sheeting. If
>  you remain concerned but cannot afford recycled lumber, you might consider
>  trying that method.
>  Gwenne

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