Durable Wood

by Bill Duesing

First broadcast on WSHU/WSUF-FM, September 27, 1996

Thankfully, if it is left outside, most wood rots. Imagine what a mess we would have if all the trees that had lived around here over the last 10,000 years were piled up where they fell. It would be quite a tangle.

Fortunately, the decomposers are ready and waiting to move into any damp piece of wood and use it as an energy and food 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, mycellium-infested mess, but it is a healthful process, a form of composting.

What if we don't want wood to rot when it is used outside. This region is home to a number of trees whose wood is rot-resistant. Eastern redcedar makes good posts for fences and pens. Its durable, red heartwood lasts for decades in the ground. The same substances that help it resist rot, make it useful for protecting woolens in chests and closets. The Atlantic whitecedar, 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, chestunt 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 after I read an article sent in by a listener. It was from Organic Gardening magazine, but drew on a large stack of government and academic reports. It also made sense. The article warned of the dangers of using pressure-treated wood to make garden beds or compost bins.

Most pressure treated lumber starts down south. After the old growth yellow pine was all cut down to make sturdy factory floors and other things, timber companies planted yellow pine in rows and stimulated its production with fertilizers and pesticides. Voilà! a quick grown lumber, not so strong or nice as the forest grown, but one that absorbs a chemical stew very well.

This wood is treated under pressure with a mixture, called CCA, of chromium and copper, two heavy metals and arsenic, a poison. This mixture of substances seems to be sufficient to keep any healthy fungi away and therefore prevents rot, at least as long as these substances remain in the wood. The problem, as Organic Gardening sees it, is that they don't stay in the wood. Arsenic is wiped off by hands and clothes, and it leaches into soil with severe negative effects. It is especially liberated by acid environments such as are found in compost and soil, as well as by acid precipitation. The article cites American and Canadian government researchers who found arsenic on every cloth they wiped over treated wood playground equipment of varying ages. It also tells of two extension agents from Texas who tested 15 samples of soil from raised bed gardens made with CCA wood. They found measurable quanties of arsenic in each sample, but somehow concluded that arsenic was not leaching from the lumber.

I talked to Bob at a plant in Massachusetts which treats lumber shipped up from the south. He said that, after treatment, the chemicals are locked up in the wood and that in 60 years of use they had never been documented to be a problem. He did note that it is 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 the ashes, ready to move around in the environment.

It's hard to know the truth. In the meantime, avoid using this lumber near compost or food plants. There are many suitable alternatives, and it seems wise not to encourage the wide spread use of arsenic.

Besides using one of the woods I mentioned, less durable wood can be coated with a mixture of linseed oil and turpentine, both plant based products which together lengthen the life of wood when it comes in contact with the ground. We frequently use recycled boards or pallets to make beds and compost bins. The wood will eventually compost and become a healthy part of the soil.

It also makes sense to seal any pressure treated lumber that children contact regularly and to think twice before buying or using any more of it.

This is Bill Duesing, Living on the Earth


This page and its contents are copyright © 1996-1997 by WSHU-FM, Fairfield, CT, and by Bill Duesing.