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Making Those Wooden Posts and Fences Last Longer PDF Print E-mail
Written by LEE REICH, For The Associated Press   
Thursday, 06 January 2011 03:28

There comes a time when every gardener needs to set wood in or on the ground.

Perhaps it's a solitary post stapled loosely with chicken wire to which a clematis or trumpet honeysuckle vine can cling. Perhaps it's one of many posts joined by high fencing to persuade deer that they can more conveniently eat from neighbors' gardens. Perhaps it's the wooden sides of your compost bin.

Wherever wood is exposed to moisture, however, it rots. Those same bacteria and fungi that keep our planet from being overrun with an accumulation of dead branches and tree trunks are not so welcome at our fence posts and trellises.

Fortunately, many ways exist to slow wood rot in the garden.

CHEMICALS CAN DO THE JOB

For finished lumber, most people these days opt for pressuretreated, or PT, wood. True, PT lumber should not rot for decades, but there are hazards associated with its use. Take care not to breathe any sawdust generated when working with this lumber, and dispose of it in the trash, not the soil.

Wood preservatives are generally toxic to more creatures than just wood-rotting bacteria and fungi, in varying degrees. Think twice before applying a preservative to wood, or using a wood treated with preservative near a vegetable garden or children's playground.

Anything that keeps moisture out of dry wood will prolong its life. Years ago, the Forest Products Laboratory of the U.S Department of Agriculture came up with just that: an effective water repellent made by combining 1 ounce of melted paraffin wax with 1.5 cups of boiled linseed oil. (Be careful when heating and mixing – both are flammable.) Once the mix cools, add enough paint thinner to make 1 gallon.

Besides this water repellant, you can buy a number of chemical preservatives that you merely paint onto the wood.

Even better is to dip the wood into the water repellant or preservative.

One reason why PT lumber is better than these home treatments is that with PT lumber, the preservative is forced into the wood under pressure at a factory. If using a store-bought or homemade preservative, apply some to the butt ends of your wood, and some will be sucked into the wood along the grain.

TRIED AND NOT NECESSARILY TRUE METHODS

Long before chemical preservatives or PT lumber were available, farmers had other ways of preserving fence posts. One traditional method was to char any parts of a post that would be in or near the ground. Bacteria and fungi have a hard time digesting charcoal, so decay was put off as long as the charred coating remained intact.

Another method was to stick the post-to-be in the ground upside down, on the theory that a piece of dead wood would suck in water in the same direction as it did when it was a part of a living tree. I wouldn't bank on it.

ROT RESISTANT, NATURALLY

Then there are woods that are naturally rot-resistant.

If you are using finished lumber, you may be restricted to choosing from among red cedar, redwood, white oak, perhaps cypress. If you can use unfinished wood – posts for a rustic pergola, for example – you can expand your palette to include such woods as black locust, osage orange, white cedar, chestnut and walnut. Black locust, osage orange, red mulberry and Pacific yew might be expected to last in or on the ground as long as PT lumber!

Note that it is the heartwood – the old, interior portion – of any tree that resists decay. So even though western larch and douglas fir are only moderately rot-resistant, the large proportion of heartwood in every log makes these woods suitable for many outdoor uses.

In contrast, Eastern red cedar is very rot-resistant, but – especially when young – has very little heartwood. Dig up an old cedar post and you will find the sapwood eaten away to a heartwood skeleton of the trunk and remnants of old side branches.

As long as the soil has yet to freeze hard, it's not too late to dig holes for garden structures and ornaments. Choose your wood carefully. And consider sticking any posts in the ground butt end up and charred.

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