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What type of treated fence posts are allowed in organic production?


There are no synthetic wood treatments currently listed as approved for organic production. Any new fencing must comply with organic standards and cannot contain these prohibited synthetic materials. However, fencing that is already in place before your first organic inspection can remain even if the posts were treated with prohibited materials. Your certifier may require a specific distance between the treated posts and soil where organic crops are grown. For your grazing animals, an interior poly fence might be required to prevent grazing right next to these posts.

Natural wood, metal, fiberglass and concrete posts are allowed. CAC-treated posts contain many synthetic compounds that are not allowed under organic regulations, including copper, ethanolamine, ammonia, and possibly formaldehyde. Copper is allowed on the National List of synthetic substances, but not specifically for wood preservation.

If you have purchased, but not yet set in place your treated posts by the day of your first organic inspection for organic certification, it is pretty likely that you will not be able to use them where they are in contact with soil growing crops that animals or humans may consume, nor where animals may touch them in any way, such as a corral or fence. Technically, you cannot set in place posts treated with synthetic materials once you are certified, which would mean the date of issuance of your first organic certificate. However, many certifiers ask that these posts not be used after your first inspection, since they will not be back to verify that you’re not using treated posts until your second inspection the following year. There is some slight variability between certifiers on how they handle this issue, but none of them allow the installation of posts treated with prohibited substances once you are certified as organic. The size of the buffer area they may require between existing or newly installed treated posts also can be different between certifiers.

Many times, the treated wood posts are preferred by some for fence corners, and I have seen certifying agencies allow this use, as long as there is a wire strung across the hypotenuse of the right triangle formed by this corner, that way, the animals stay back from the corner where the wooden posts are located and cannot consume grass near the wood.

All of these treatments do leach into the soil, and plants have been known to accumulate the synthetics in their vegetative matter. This is especially an issue in organic orchards. Stabilizing posts placed next to new trees should not have any synthetic treatments. Perimeter fencing around an orchard usually would be far enough away from your trees that treated wood may be used, but the distance required can vary between certification agencies. Many times, the dripline of the outer branches of a mature tree would be sufficient distance to the treated post. To be sure, check with your certifier about the required distance to maintain between treated wood fenceposts and your trees before you install perimeter fencing. Also ask what date they will allow the installation of treated posts in close proximity to your organic plants or grazing area before you are officially considered a certified organic operation.

Posted: Jan 2010
Answer By: Harriet Behar