1, 2005: I was working on my grape arbor the other day
and noticed that some of the posts need to be replaced. We use the
grapes to make jelly, juice, and homemade wine. We don’t sell
any of the grapes or grape products, but we still follow organic
standards and we have the grapes listed on our Organic System Plan.
So I need to use rot-resistant posts, but according to organic
regulations I can’t use posts treated with copper chromium
arsenate or creosote. This is a common dilemma faced by many organic
vegetable, fruit and livestock producers.
The National Organic Standards, in section 205.206(f) state, “The
producer must not use lumber treated with arsenate or other prohibited
materials for new installations or
replacement purposes in contact with soil or livestock.”
My posts will be used for replacement purposes, and they will contact
the soil, so I must not use lumber treated with arsenate or other
prohibited substances. How do I know which types of posts on the
market are treated with prohibited substances?
Pennsylvania Certified Organic (PCO) reported in their Spring 2005
newsletter, Organic Matters, that they reviewed four wood treatments
and found that all contained prohibited substances. They were:
- Natural Select® Wolmanized Wood
- Copper Azole Wood Treatment (CBA)
- Preserve® and Preserve Plus® (AQC)
- Akaline Copper Quaternary Ammonium
So now I know what I can't use—what can I use?
ATTRA (Appropriate Technology Transfer to Rural Areas) also has
an informative booklet, titled Organic Alternatives to Treated Lumber,
posted at http://www.attra.org/attra-pub/lumber.html.
According to the ATTRA publication, chromated copper arsenate (CCA),
often referred to as “pressure-treated lumber,” is most
commonly available in retail outlets. The CCA mixture, which contains
copper, arsenic, and chromium compounds, is dissolved in ammonia
and then forced, under high pressure, deep into the wood.
Arsenic, chromium, and copper do leach from treated wood. Arsenic
can collect in the soil under most CCA-treated wood applications.
Burning CCA-treated wood volatilizes some of the arsenic, but the
ash remaining is technically a hazardous waste. Disposal of CCA-treated
wood to landfills may be potentially dangerous because as the wood
rots in the landfills, the metals are released and may pose a threat
Recent studies have shown that arsenic can be absorbed through
the skin from contact with treated wood. The results of prolonged
exposure to arsenic can include vomiting, diarrhea, nerve damage,
blood vessel damage, and heart rhythm dysfunction (Rodale, 2000).
Arsenic is also an extremely potent carcinogen, and chromium is
a suspected carcinogen.
Because of the health concerns surrounding CCA-treated wood, the
U.S. Environmental Protection Agency implemented a ban on its manufacture
and sale for residential applications effective January 1, 2004.
Many of the "alternative" treated wood products (such
as those listed above that were tested by PCO) also contain substances
prohibited in organic systems, however.
Cooperative Extension of the University of Nebraska-Lincoln has
a publication, Native Wood Fence Posts (Schmidt and Kuhns, 1990),
that lists the expected lifespan of many untreated wood species
used for fence posts, along with information on some of the advantages
of seasoning posts before use. See http://ianrpubs.unl.edu/forestry/g314.htm.
According to the Nebraska publication, the best species for use
as fence posts without treatment are osage orange, also known as
hedge (>35 years), black locust (>20 years), and eastern red
cedar (>20 years).
Besides untreated wood fence posts, other options include plastic,
plastic/wood composites, steel T–posts, steel pipe, concrete,
fiberglass, or even concrete–filled plastic pipe. These fence
posts will vary in cost, availability, and practicality for each
specific fencing need.
Many plastic fence posts are made from recycled plastic containers.
They come in various lengths, dimensions, and colors; can be stapled,
drilled, or cut like wood; and are self-insulating for electric
If you already have treated wood posts in your field, garden, arbor,
or orchard, you are “grandfathered in.” However, if
the treated wood comes in direct contact with crops or livestock,
it may present a contamination risk, and you might need to remove
or replace it. As always, check with your certifying agent.
When it's time to replace wood treated with prohibited substances
or put in new posts, you must use approved materials in order to
follow the organic standards.
Osage orange doesn’t grow in my area, but we have plenty
of eastern red cedar. We have been clearing a savannah prairie of
red cedar and buckthorn, so I’ll use the red cedars for posts
in my vineyard.