Growing & Winemaking
Alternatives to Wood Posts
Many a summer afternoon spent mending fences on my brother’s dairy farm taught me the value of cedar posts. Sometimes we would strip bark off the logs that would eventually be formed into stakes, on which we hung electric wire to keep the cattle in. The lifespan was a dozen years, maybe more. There simply wasn’t anything as durable when it came to fenceposts—certainly nothing as cheap as logs from my brother’s own property.
It’s a story many vineyard owners today can relate to, whether or not they own woodlots. Wooden posts are still a common means of anchoring trellising wires in North American vineyards—in sharp contrast to Europe, where wood is also traditional but now an old-school material for posts.
Exhibitors showing off vineyard supplies at Enovitis, the viticultural show that runs alongside the biennial SIMEI exhibition of winery equipment in Milan, Italy, this past fall offered posts made from everything from wood to fiberglass.
While wood has its champions as a traditional, renewable and biodegradable resource, other materials offer long-term cost advantages and environmental benefits that many growers find attractive.
The shift began happening 40 years ago when traditional viticultural practices gave way to newer, cost-efficient practices both by equipment manufacturers and in the vineyard itself. The rise of concrete and cheap oil allowed for the production of posts from these materials in Europe at prices lower than lumber mills could produce posts.
Moreover, the shorter lifespan of wood made rot-proof concrete, metal and plastic posts more appealing. With life-spans of 30 years and more, the new materials trumped traditional wood posts not only in the up-front investment but also long-term maintenance and replacement costs.
Comavit Pali Precompressi SRL showed posts made from concrete, plastic and steel, as well as wood. Serving both orchards and vineyards, Comavit says pre-stressed concrete is the most popular material for post fabrication.
Unlike reinforced concrete, which incorporates steel reinforcing bars (rebar) to strengthen cement for use in various forms of construction such as bridges and high-rises, pre-stressed concrete has additional strength that allows it to support greater spans than ordinary reinforced concrete. What this means in the vineyard are strong end-posts that can support lengthy training wires and fruit-laden vines. Standard reinforced concrete isn’t resilient enough to withstand the same pressures, reducing its endurance and potentially increasing the frequency of replacement.
Comavit claims that its pre-stressed concrete posts are resistant to shocks, wind gusts, atmospheric agents and chemical inputs used in the vineyard. They also increase the potential for mechanizing the vineyard operation: Hit a concrete post with a tractor or harvester (we don’t recommend it), and it will likely suffer less damage than a wooden post, which is more likely to need replacement.
Ditto for metal posts, which will likely bend if you run into them with equipment (again, not recommended). However, metal posts are typically fabricated to have elevated resistance to wind stress and other factors, depending on the vineyard site. While metal posts may suffer from the effects of tension stress, they’re typically treated to be rust-resistant. Comavit offers galvanized iron and steel posts. The latter are often treated with a polyester spray paint that can extend the post’s life as much as 30%, to a maximum of about 30 years.
A company with its roots in the earliest days of the shift away from wooden posts is Cassi Manufatti Cemento SRL, established in 1970. It produces pre-stressed and vibrated concrete posts: The latter are compressed through vibration to eliminate weaknesses. An added effect of vibration is smooth posts with uniform shapes that also facilitate mechanical harvesting.
| Most seek the look of wood
Small wonder, then, that the majority of vineyard post producers offer a wood-like finish regardless of the material from which the posts are fabricated. While most posts are designed to accommodate mechanization of vineyard labor, the visual impact growers want is one of ancient tradition. Spray painting is one option for ensuring metal posts are unobtrusive additions to the vineyard. Usually, the paint incorporates chemicals designed to increase the post’s resistance to the elements and chemical inputs. Plastic posts from Palolite are created to mimic the size, color and roughness of traditional wood posts, thanks to the adaptable character of plastic. But the stainless-wood posts by CMC offer an attractive hybrid solution: Posts that benefit from rot-reducing steel sleeves at the base, while still offering turned pine shafts above that provide not just the appearance of wood but the real thing. P.M. |
Other creative alternatives
One of the newest additions among CMC’s post offerings is a stainless/wood post, introduced in 2007. Scots pine posts fit into crimped stainless steel sleeves designed to prevent rot at the post foot. The sleeve is “crushed” onto the wood to ensure a uniform diameter along the shaft of the post. “This creates a certain continuity in the external surface, so that rain runs off the outer surface without pooling or penetrating inside,” CMC’s catalog states. This extends the post’s lifespan, reducing long-term cost for growers while maintaining a traditional aesthetic.
A traditional look is also a selling point Palolite SRL touts for its plastic stakes, which mi
mic the size, color and roughness of wood stakes. However, the resin is resistant to weathering, giving growers a more durable option than wood.
Safety is another feature of plastic posts, which neither splinter nor rust as do their wood and metal counterparts. The posts’ smooth texture reduces risk of injury to workers’ hands, and plastic is more flexible than steel or concrete, limiting the risk of damage to equipment through inadvertent contact.
A fourth alternative to wood is fiberglass. NTET S.p.A. parlays its experience developing fiberglass products for the telecommunications sector into designs for grapegrowers.
Environmental questions
A question facing almost all alternatives to wood is the environmental impact. While wood is seen as requiring less energy to produce, and is prone to biodegradation, many posts are treated with chemicals designed to lengthen their lifespan. These chemicals may leach into the soil and adjacent watercourses. This compromises the green credentials of wooden posts, prompting many manufacturers to highlight the environmental merits of the posts they do offer.
CMC, for example, notes that its steel-wood posts are “ecological,” being protected against rot at the base by the steel sleeve and treated with preserving salts. Galvanizing solutions for the metal posts are lead-free, “in respect of future standards for environmental protection.”
Similarly, Palolite claims that its posts don’t release any noxious substances and can ultimately be recycled rather than sent to a landfill. It also adds that the intrinsic strength of the posts reduces the number required to support vines, thereby reducing overall material costs.
While reduction and reuse are important, concrete posts offer the added advantage over metal and plastic of requiring mere crushing prior to reuse in building foundations or as aggregate on construction sites. This is the common destination of Comavit’s posts.
It’s different in America
While metal anchor posts are available from many suppliers in North America, the availability of wood keeps it a popular choice and holds alternatives to a minimum. The volume of posts imported from Italy is low; even less with the shift in exchange rates that has reduced the dollar’s buying power abroad.
Still, metal is claiming market share on this side of the Atlantic. The past two years have seen a “strong move” among growers to metal, says Dan Drake, vice president of vineyard operations with Jim’s Supply Co. Inc. in Bakersfield, Calif. Cost is less of a factor than grower preference, which typically favors the long-term cost and lifespan of the post.
A producer in Canada was supplying plastic posts a few years ago, Drake says, but these didn’t catch on because their weight boosted shipping costs and made handling awkward in the vineyard. Chinese-made composite posts, which mix concrete and plastic, are available but expensive, and they haven’t caught on with growers. Drake says it’s a different story in Mexico and parts of Europe, where the materials for composite posts are often more readily available than metal or wood.
Drake suspects a factor in U.S. growers’ shift toward metal has been the changing regulations regarding wood preservatives. Softer treatments mean metal posts and stakes are now more cost-effective over the long-term, especially when labor costs are factored in.
The latest wood posts just don’t have the longevity of those produced in previous decades, he says. “I looked at some posts this past weekend that were put in 25 years ago, and they look like new posts still. I look at posts that were put in five years ago, and they’ve got about a five-year life left.” In contrast, steel is a fairly consistent product, according to Drake. Moreover, steel posts typically incorporate salvaged metal and are themselves recyclable.
Still, growers’ partiality to wood is shown in the kind of finishes they choose. Galvanized steel is durable, but Drake said that growers—if site conditions allow it—are keen on posts that mimic wood. Black iron stakes may have a shorter lifespan than galvanized steel, but Drake says they’re attractive to some growers because they blend in with the vines when they’re new and mimic the color of wood as they weather.
“We’re one of the few nations that still likes the black stake because it looks closest to wood—that burnt orange look when it rusts out.”
Our Northwest correspondent Peter Mitham is a freelance agriculture writer based in Vancouver, B.C. Look for his weekly dispatches at winesandvines.com Headlines. Contact him through edit@winesandvines.com.
