By The Old House Web


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.


"Using Treated Wood Around The Garden" Michael A. Kamrin Center for Environmental Toxicology Michigan State University

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