We selected our garden marker and nameplate materials based upon a 27-question survey completed by over 1,300 gardeners, our own experiences at Hostas Direct, Inc. and by using and testing various plant identification products.
Gardeners prefer stainless markers because they will not rust. Stainless steel provides the most tensile strength allowing the use of a thinner yet stronger stake (allowing longer lengths) which is unobtrusive and blends into your garden. T304 stainless steel provides superior resistance to corrosive agents in the garden such as:
Our stainless steel stakes are approximately 18% chromium and 8% nickel. T304 stainless is the most corrosive resistant of the stainless steel group of metals. T304 stainless steel contains a minimum of 10.5% chromium that makes it resist rust or stain better than other types of steel. The chromium in the steel combines with oxygen to form a thin, invisible layer of a chrome oxide called the passive film, which is only a few atoms thick. If the metal is cut or scratched and the passive film is disrupted, more oxide will quickly form and protect the metal from oxidative corrosion. Iron, on the other hand, rusts quickly. Our markers do not need an additional protective coating. Bending steel with a protective coating might crack the coating and expose the steel underneath, creating unsightly rust, weakening the product, and make it unusable.
The corrosion of bare steel in soils varies significantly based on the type and location of the soil. The corrosion rate of plain carbon steel in soil can range from less than 20 microns (.8 ml. or .03”) per year to 200 microns (8.0 ml. or .31”) per year or more!
We've been disappointed with zinc markers because they do not provide the long-term attractiveness needed for permanent plant identification. The term ‘zinc’ coating typically refers to hot-dip galvanizing, a metallurgical process that is used to coat steel or iron with zinc.
Due to various physical and chemical characteristics of soil, it is extremely difficult to predict underground corrosion rates. Hot-dip galvanized steel will not perform as well in soils containing large amounts of organic bacteria due to the bacteria's consumption of oxygen. In order to predict the performance of hot-dip galvanized steel in soil, you have to classify the soil, which can vary in content even in close proximity. Studies have shown soil pH to vary from 2.6 up to 10.2. Hot-dip galvanized steel performs the best in soils that are neutral or slightly basic. In general, sandy, well-aerated soils with a neutral or slightly basic pH will cause only limited corrosion of zinc, most likely below 10 microns (0.4 mil or .01”) per year. Plentiful rainfall typically leads to soil that is more acidic and more corrosive to zinc. The longer galvanized steel remains wet, the higher the corrosion rate.
The traditional measure of a coating's effectiveness is resistance to a salt spray. Thin coatings cannot remain intact indefinitely when subject to surface abrasion, and the galvanic protection offered by zinc can be sharply contrasted to more noble metals. A scratched or incomplete coating of chromium actually exacerbates corrosion of the underlying steel, since it is less electrochemically active than the substrate. The properties of soil that have the most effect on the corrosion rate of zinc are aeration, moisture content (or time of wetness), pH, temperature and resistivity.
Information from: www.galvanizeit.org/aga/about-hot-dip-galvanizing/how-long-does-hdg-last/in-soil
Carbon steel will quickly rust without a protective coating. According to the American Iron and Steel Institute (AISI), steel is considered to be carbon steel when no minimum content is specified or required for chromium (needs 10.5% to be a rust preventer), cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect." The term "carbon steel" may also be used in reference to steel that is not stainless steel, which means that carbon steel may include alloy steels.
Powder coating is a type of coating that is applied as a free-flowing, dry powder.
While powder coatings have many advantages over other coating processes, there are limitations to the technology.