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RE: Use of treated lumber not recommended for vegetable raised beds

  • Subject: RE: [cg] Use of treated lumber not recommended for vegetable raised beds
  • From: Gwenne Hayes-Stewart <Gwenne.Hayes-Stewart@mobot.org>
  • Date: Mon, 31 Dec 2001 15:00:09 -0600

Title: RE: [cg] Use of treated lumber not recommended for vegetable raised beds

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 fifteen 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.  So 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.


-----Original Message-----
From: Greg Lecker [mailto:glecker@michaudcooley.com]
Sent: Monday, December 31, 2001 2:33 PM
To: community_garden@mallorn.com
Subject: [cg] Use of treated lumber not recommended for vegetable raised

The use of pressure treated lumber for raised vegetable or fruit
planting beds is not recommended, as evidenced by the
following information which I summarized from the Minnesota
Master Gardener List Serve Archives. Uses for non-edible
landscaping seem to be possible, although precautions are still

Alternative long-lasting materials for raised beds are cinder
blocks, interlocking landscape blocks, redwood, cedar,  plastic
lumber, "Trex" (made from wood and recycled plastic), the sky's
the limit.

CCA lumber is also called pressure-treated lumber or "green"
lumber.  It does have a green cast to it.  CCA stands for
chromated copper arsonate (copper, chromium, and arsenic are
all toxic metals at elevated concentrations).  I understand that
there is research being done to look at the fate of the arsonate in
soil surrounding very old timbers, but so far I've not heard of
conclusions having been drawn.   Now the timbers have been
pressure-treated, and the chemical is bound tightly into the wood
at least in landscape timbers that are not so old they are
beginning to deteriorate.  However, to my experience, if I were
to walk through an area of a lumberyard where such treated
wood is stored I would definitely detect an odor of the CCA
chemicals.  This is an indication that some fraction of the CCA
treatment is mobile in the environment.  It is also true that ALL
compounds tend to dissolve in groundwater to some extent.  I
would NEVER surround veggies with CCA treated lumber.  I'm
not sure if enough research has been done to indicate just how
much arsenic leaches into the soil.  However, a director of a
child development center in North Carolina mentions that her
state mandated several years ago that there can be no CCA play
structures in the playgrounds.   There is a test that can be done to
determine how much arsenic is in the soil around the play
structures, so some arsenic must be leaching out.

Creosote is thought to be carcinogenic, gloves are recommended
when handling railroad ties, and face masks to cover your nose
and mouth are recommended when cutting them.

While it's true that for non-edible landscaping, some non-edible
plants -- grass, shrubs, flowers -- are not bothered by the fumes
given off by creosote-treated timbers.  Others, more sensitive,
can be damaged.  I know of no list that distinguishes between
them, however.  It would be pretty much trial and error.  Use of
"older" creosote-treated ones that don't give off much in the way
of fumes (on a hot day) may be a solution for non-edible
landscaping needs.
Greg Lecker
A Vision of Michaud Cooley Erickson
Suite 1200
333 South Seventh Street
Minneapolis, MN  55402
Fax: 612.339.8354

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