Botanica Atlanta | Landscape Design, Construction & Maintenance

Generally speaking, rusted metal is not something to get excited about. The rusting of metal, the oxidizing on iron-containing manmade products, has mental associations with failure and rot, but there is one material that puts this oxidation to good use. “Weathering steel,” more commonly referred to by some variation of its proprietary trademark, Corten, is a material that is intended to form a rusty outer skin.

 Image: Roger McLassus

Unlike most iron-containing metals, Corten steel does not require painting to withstand the elements. In fact, the rust that forms on the exposed surfaces of this type of steel acts as a protective paint. Due to a special recipe, when this alloy is assailed by the elements, a thin outer layer of steel rusts and then prevents the interior from doing the same. I certainly cannot claim any training in metallurgy, but the properties of typical steel compared to Corten seem to bear a resemblance to the corrosion differences between cast iron and wrought iron.

In addition to weathering steel’s tendency to resist rust, it is also a very strong alloy. Corten’s name is derived from the first three letters of its two distinctive qualities; it has outstanding corrosion resistance and tensile strength. These properties make the metal a solid choice for a variety of architectural and engineering applications. Corten’s first appearance on the architectural stage was in 1964 with Eero Saarinen and Associates groundbreaking design for John Deere World Headquarters in Moline, Illinois. Another significant weathering steel structure is the New River Gorge Bridge in West Virginia’s Appalachian Mountains.

Images: Michael Dant and Ja Ga

In the world of public-realm sculpture, weathering steel is significantly more common. Just a few years after the John Deere Headquarters was completed, Pablo Picasso created one of the most celebrated public Corten compositions.His untitled work, often nicknamed “Chicago Picasso,” still stands today in Chicago’s Daley Plaza. Other artists, including Richard Serra and Bernar Venet have built entire public-sculpture careers on the backbone of this unconventional material.

Images: Umit Kivanc, Lump Sculpture Studio, and Sam Valentine

Unfortunately, even weathering steel is not entirely immune to corrosion problems. The most common problem is the unanticipated rust stains that rainwater can splash onto nearby stone, concrete, or wood surfaces. In a few cases, flawed structural design or even chemical makeup have caused the oxidizing reaction to continue uninhibited. A poorly designed Corten object might never stop rusting.

Images: Considered Design and Planterworx

In the garden, weathering steel can take on a variety forms. A quick internet search will turn up some excellent precedents of the material’s many landscape possibilities. Corten can be used to construct garden edging, planters, retaining walls, and sculptural objects. A handful of landscape architects, including Mikyoung Kim and Andrea Cochran, have used the material masterfully and helped to redefine its potential.

Images: Considered Design and Planterworx

Depending on your garden’s climate and how many years of exposure a weathering steel surface has survived, Corten can offer a range of hues, from deep ruby-purples to flat, terra cotta oranges. As I acknowledged earlier, rust is usually nothing to celebrate, but to the informed eye, weathering steel objects, with their self-healing, regenerative, and self-protective properties, can be just short of magical.

Author: Sam Valentine, BLA, LEED AP