Thankfully, most wood rots if it is left outdoors exposed to the elements. Imagine what a pile up we would have if all the trees that had lived around here over the last 10,000 years were still lying where they fell: not a pretty sight.
Fortunately, the decomposers are ready to move into any damp piece of wood and use it as a nutrient and energy source. In the process, they take the wood apart, adding humus to the soil and returning carbon dioxide and water to the air. Admittedly, rotting wood can be a slimy, mycelium-infested mess, but the process is beneficial.
What do we do if we don't want wood to decompose when it is used outside? Our northeastern region is home to a number of trees whose wood is rot-resistant. Eastern Red Cedar makes good posts for fences and pens. Its durable, red heartwood lasts for decades in the ground. The same substances that help it to resist rot also make it useful for protecting woolens against moths in chests and closets. The Atlantic White Cedar, which is often used for shingles and telephone poles, grows in freshwater swamps along the Atlantic Coast.
Earlier in this century, many beautiful garden structures were made of Black Locust, another very rot-resistant wood which is quite common on Long Island and in Connecticut. White oak and Catalpa woods are also very durable. And, until they were wiped out by an imported blight early in this century, Chestnut trees provided long-lasting fence posts and rails, as well as wood for barns and cow stalls.
I got to thinking about these durable woods when I read an article from Organic Gardening magazine about pressure-treated wood, sent to me by a listener. The article, which was based on both government and academic reports, warned of the dangers of using pressure-treated wood to make garden beds or compost bins.
Here's the story. Most pressure-treated lumber begins its life down south. After the old-growth, yellow pine was all cut down, primarily to make sturdy factory floors, timber companies planted yellow pines in rows and vigorously stimulated their production with fertilizers and pesticides. Voila! A quick-grown lumber, not as strong or as durable as the forest-grown trees, but very suitable for absorbing the chemical stew which is injected into it under pressure.
The chemical mixture, called CCA, contains two heavy metals (chromium and copper) and a poison, arsenic. This toxic mixture is sufficient to repel most wood-rotting fungi. Decomposition is avoided as long as these substances remain in the wood. The problem, however, as Organic Gardening describes it, is that CCA doesn't stay in the wood. Arsenic wipes off on hands and clothing, and it leaches into soil with severe, negative effects. The poisons in pressure-treated wood are liberated by acid precipitation, as well as by the acid environments found in compost and soil. The article cites American and Canadian government researchers who found arsenic on every cloth they wiped over playground equipment of varying ages made from treated wood. It also reports that 15 samples of soil from raised-bed gardens made with CCA wood had measurable quantities of arsenic in every sample.
It is especially important not to burn pressure treated lumber. Once burned, the chemicals are no longer locked in the wood; they end up in the air or in the ashes, ready to move around in the environment.
Let caution be your guide and avoid using pressure-treated lumber near compost or food plants, at the very least. There are so many suitable alternatives, and it seems wise not to encourage the widespread use of arsenic and chromium.
Besides using rot-resistant woods, less durable lumber can be coated with a mixture of linseed oil and turpentine, both plant-based products. This treatment lengthens the life of wood, especially when it comes in contact with the ground. We frequently use recycled boards or pallets to make garden beds and compost bins. The wood will eventually decompose and become a healthy part of the soil.
Learning to take advantage of the special properties of local trees is an important step in reconnecting with the environment.
This is Bill Duesing, Living on the Earth
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