Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001917
11/12/99
USING TREATED WOOD AROUND THE GARDEN
Wood borders are attractive enhancements to the home
garden. However, their attractiveness wanes as the wood
becomes decayed. The use of treated wood as a home garden
border is a practice growing in popularity, allowing the
home gardener attractive borders without fear of decay.
Wolmanized wood is the most commonly available treated
wood. The wood is impregnated with a combination of
chemicals known as CCA (chromated copper arsenate), which
serve to protect the wood from attack from agents such as
fungi, which can shorten the useful lifetime of the wood.
However, protection against decay is not without its
price. There are toxin effects resulting from high
exposure of the chemicals. Such exposure may contaminate
fruits and vegetables that are eaten by the growers.
Under normal conditions, the risk of contamination is low.
The chemicals are forced into the wood at very high
pressure and remain effectively bound to the wood for very
long periods of time, allowing only very small amounts of
these chemicals leak out and get into the soil. Some
elements do not move rapidly through the soil, resulting
in limited migration. These elements are: arsenic,
chromium, and copper. Movement from treated wood would
not be expected to cause a significant increase in the
normal background levels of these elements.
Slow moving elements could have an effect on plant roots.
Plant roots growing within 6" of treated wood could have
slightly higher levels of copper and arsenic. The effect
is dependent on the plant species, the volume of soil in
close proximity to treated wood, and the soil fertility
conditions. Due to the general unavailability of chromium
in soils, no increase in plant uptake of this element is
expected.
Although precautionary barriers are not really necessary,
they provide extra protection. The inside of the wood can
be lined with heavy duty plastic as a means of protection,
or the wood could be coated with an appropriate sealer.
SOURCE:
"Using Treated Wood Around The Garden"
Michael A. Kamrin
Center for Environmental Toxicology
Michigan State University
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