BioGro Number 5365

Australian company WoodShield has achieved BioGro certification for its polymer-encased timber posts, which offer more strength, durability and flexibility than conventional treated timber posts – without the toxic drawbacks of treated timber.

In 2010, New Zealand’s organic growers faced a dilemma. The USDA announced that farms selling organic products in the US would no longer be allowed to install chemically treated timber. At the time, few non-toxic alternatives existed in New Zealand with the availability and versatility to fit immediately into existing farming operations. WoodShield has stepped in to help fill this demand.

The USDA prohibition applies to lumber used in direct contact with organically produced and handled crops and livestock, such as vineyard posts and livestock fencing. (It doesn’t extend to uses such as lumber for building materials that are isolated from the certified organic production area.)

The standard treated timber posts on most New Zealand farms have been pressure-injected with copper chromium arsenate (CCA). This wood-preserving cocktail is highly toxic. Copper and chromium are preservatives, but they are also heavy metal contaminants which can leach into soil. Arsenic is the ingredient of greatest concern; it can leach into groundwater supplies, and chronic exposure is associated with various cancers. Arsenic has been detected above established safe levels in soil tests in Marlborough vineyards that use CCA posts. It is also toxic to insects, frogs and other wildlife.

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In 2003, our Australian team went looking for a safer alternative. The idea was to take untreated pine posts and cover them in a polymer shield instead of pumping chemicals into them.

We initially designed the posts for vineyards. It took approximately three years to develop and refine the production process, but the approach has now been proven to work in all agricultural applications, and WoodShield Pty Ltd has worldwide patents in place.

We machine untreated pine posts to 75mm, 93mm and 113mm diameters. Then we apply a protective layer of UV-resistant pipe-grade polyethylene, encasing the posts to finished sizes of approximately 83mm, 100mm and 124mm respectively.

The process creates a strong adhesive bond between the timber and the polymer, completely sealing the post, leaving no timber exposed.

The result greatly increases the timber’s overall strength. We had Melbourne Testing Services complete ‘Three Point Bending Tests’ on the WoodShield posts. It took 40-50% more force to break our posts, compared to treated pine posts of the same size.

The breakage deflection angle is also approximately twice that of normal posts. This means that the post bends more before it breaks; it’s more likely to flex and bend than to crack and snap. Breakages at ground level from mechanical harvesting have been significantly reduced.


You can still nail them, screw them, whack them and knock them in the ground. We protect the post ends with thick end caps, enabling the posts to be hydraulically driven into the ground, just like a standard timber post.

So we’ve improved on many problems of chemically treated posts, such as warping, splitting, chemical leaching, rotting and breaking at ground level, making WoodShield posts a better option than CCA posts in numerous ways.

Our products are now used widely in organic viticulture, standard viticulture and dairy farming. We’ve also just started working with the kiwifruit industry in the Bay of Plenty, and the oyster farmers around Waiheke Island. Equine fencing is another use, as are park surrounds, playgrounds, jetty posts and many landscaping projects.

The first WoodShield vineyard posts were installed in 2004, and are still going strong more than a decade later. Twelve years after installation, we visited the first vineyard, and it looked just the same as the day the posts went in. The coating that we use on the posts is medium density polyethylene and is UV-stabilised; it’s incredibly resilient and long-lasting. This is the same polymer that is used in gas pipelines, which have to take a beating in the desert and last for at least 50 years.