Anyone have experience with using galvanized steel livestock troughs as raised garden beds?
I’ve been pricing materials for raised beds and searching online for what other gardeners have used: the costs and designs. One idea that caught my eye was using livestock troughs as planters.
Online, I’ve seen 20 gauge galvanized steel livestock watering troughs measuring 3 feet by 10 feet, 24 inches tall for about $240.
Advantages: Less expensive than using some long lasting wood boards, ready to use, taller beds make gardening easier for all. The height of the bed should discourage rabbits and the bottom should keep voles and moles out. Lifespan: 5 to 20 years.
Disadvantages: Some websites posted concerns about zinc leaching into the soil. So I did what journalists do, I researched.
Alana Hochstein, a corrosion Engineer with the American Galvanizers Association noted in an email “The Food and Drug Association (FDA) has approved the use of galvanized steel for food preparation and conveyance for all applications with the exception of foods that have a high acid content, such as tomatoes, oranges, limes, and other fruits. For more information, see our website:
The National Gardening Association (https://garden.org/about/intro/president)
I emailed NGA President David Whitinger about whether zinc was a concern. He wrote: “Plenty of people use galvanized containers for gardening and I’ve never heard of anything to suggest that it’s not safe.”
I also noted online that community gardens and restaurants are using galvanized steel as beds. Still, I needed more information.
I looked for data from Cornell University. Cornell soil extension agent Robert R. Schindelbeck emailed: “The zinc can leach from the metal object into the soil. Generally this is OK as zinc is relatively “safe.” He referred me to this link titled Healthy Soils, Healthy Communities:
“What levels of metals are acceptable in garden soils?
“There are no standards protective of public health specifically for metals in garden soils in NYS, but there are guidance values developed for other purposes that gardeners can consider.”
Zinc is naturally occurring. The NYS Department of Environmental Conservation and the NYS Department of Health developed guidance values. The guidance values for zinc are 2200 parts per million (PPM). Levels found in NYS soils in rural areas were 10-140 ppm and in urban areas 64-380 ppm.
“Human health: Small amounts of zinc in the diet are essential for good health.
“Plant health: Zinc is an essential micronutrient for plants, but it can be toxic to plants at higher soil levels, even below those that are a concern for human health.”
That begs the question: What are the zinc levels for soil in a galvanized trough? This question gets answered by the fourth source: Rodale’s Organic Life article written by Deb Martin, November 13, 2014
Is it safe to use galvanized sheet metal to build raised garden beds? —Susan Taylor, Monticello, Utah
Over time, compounds used in the galvanizing process will leach from galvanized metal into surrounding soil. Climate and soil conditions such as moisture and salinity affect the rate and the amount of leaching. While the by-products of corrosion are unlikely to occur in amounts that pose any risk to human or plant health, gardeners who are considering growing in galvanized containers or metal-framed beds should be aware of the potential for zinc and other materials to transfer into the soil.
Zinc, the main ingredient in the galvanizing “bath” used to prolong the life of steel, is an essential micronutrient that occurs naturally in North American soils at an average background level of 0.07 milligrams of zinc per gram of soil. For the sake of comparison, the Daily Value (an approximation of our dietary need) for zinc established by the FDA for adults is 8 to 11 milligrams.
While studies of zinc levels in the soil next to galvanized structures have found increased amounts of the element, those levels often are comparable to background levels and within EPA guidelines, says Dan Barlow, a corrosion engineer with the American Galvanizers Association.
Zinc does not migrate readily through soil, so elevated zinc levels tend to be found only in the immediate area of a galvanized container or structure. Soil pH, organic matter content, and other soil characteristics affect zinc’s ability to be taken up by plant roots. As much as 90 percent of zinc in soil may be unavailable for uptake by plants.
Due to zinc’s limited bioavailability in soil, there is little chance of ingesting too much zinc through plants grown in proximity to galvanized metal, says Eric Van Genderen, Ph.D., manager of environment and sustainability for the International Zinc Association. “You will likely never get even your recommended daily allowance from your produce, much less too much,” he says.
Because galvanized metal corrodes faster as pH decreases, Van Genderen says it’s probably not the best container material for plants that require acidic conditions.
Other corrosion by-products may show up in the surrounding soil, Van Genderen says. He notes that levels of other metals found in galvanized surfaces, such as nickel and bismuth, typically would be “so low that you’d probably never see a difference in the amount coming from the galvanized metal versus the background levels.”
The health of beneficial soil microorganisms that are exposed to galvanized metal is another consideration. “There is no question zinc can kill some of the soil’s microbes and that others love it,” says Jeff Lowenfels, author of Teaming with Microbes: The Organic Gardener’s Guide to the Soil Food Web, Revised Edition (Timber Press, 2010), and Teaming with Nutrients: The Organic Gardener’s Guide to Optimizing Plant Nutrition (Timber Press, 2013). “I am willing to let the arbuscular mycorrhizal fungi take up excess zinc, feed the plants what they need, and hold the rest,” Lowenfels says. His research has convinced him that “any damage done to the soil food web [by excess zinc] is quickly corrected by it if the soil food web is a healthy one.”
Troughs in the Garden
Want to see more?
If you search Google, you’ll find dozens of examples of troughs that have been painted and made pretty.
The nicest I’ve seen is at http://www.nwedible.com/the-most-attractive-veggie-garden-ever/. Check it out.
Tips on Painting a trough: https://www.gardenista.com/posts/steal-this-look-water-troughs-as-raised-garden-beds/
Tips on making a trough self-watering.