Since we wanted the steel to eventually weather to a dark color, we didn't want to go with the corten steel that remains pretty orange. This is Oregon mild steel. I assume that means mild steel from Oregon. There were some steel workers doing some interior work on the home and I used them as a resource to help me understand and find what we needed. Mild steel.

Many thanks. What thickness you have used.

This steel is 1/2" thick. The top three tiers of steel are 36" tall, leaving 24" above grade and 12" in the ground.

Beautiful. What technique did you use to keep the steel in place?

The plates are concave so the soil pressure from behind only pushes them more firmly into the boulders on each end. Mostly though, they are held in place by the 12" of buried steel that you can't see.

Hi Kevin. Beautiful work. My question: wouldn't the steel "leakage" through oxidation produce chemicals that have a detrimental effect on the soil and eventually on the plants? Excuse my ignorance on any basic chemistry.

None that I am aware of. I haven't researched this though. I imagine there will be more iron in the soil. And I've heard of people putting nails on the ground around their hydrangeas to change their flower color (makes the ground more acidic I presume). Maybe I should research first, then comment. Too late!

The only info I could find surfing out there was how soil affects the corrosion of steel, not vice versa. And though people bury rusty nails around hydrangeas, it doesn't really change the pH like they think it will.

I'd love to know how thick the core ten steel is? I'm researching options of our front yard in Auckland New Zealand.

It's 1/2" mild Oregon steel and we expect it to turn a dark dark brown.
I loved Auckland! I studied Landscape Arch. at Lincoln Univ for a year and spent every weekend, break and holiday hitchhiking both islands.

Thanks Kevin. Glad you enjoyed your time in NZ. Now I just need to find a supplier. so far I can only find 6 mm which is just over a 1/4 inch.

hi, wonderful work... quick question... did you dig a one foot ditch for this project?

Pretty much. We actually terraced the slope at 12" below grade for each wall, Then we set the steel plates on the subgrade about 12" in front of where the subsoil stepped up and backfilled behind the walls with drainage. This left us 12" for topsoil. Make sense? Digging a ditch should work fine.

great info. I am trying to do a similar thing with our yard but plan on using a smaller retaining wall. I posted a question here and I am wondering if you can offer any advice on how we can go about doing this https://www.houzz.com/discussions/how-can-i-diy-corten-steel-edge-retaining-wall-dsvw-vd~1011573

I would suggest going directly to a steel yard and getting what you need. They likely won't have corten in stock, but if regular mild steel is okay then you can probably get lengths of steel at 1/4" thick as wide as 12".

Kevin, I've found it very difficult to locate Corten in the Seattle area and was told by a steel yard that it's probably not worth the hassle and expense of hunting for it. I have low steel walls - 18 to 20 inches in height - that I plan to backfill with gravel and a French drain, as you have. Do you think regular 1/4-inch plate steel will last? How long before it rusts through?

Nickwingy - proper weathering of CorTen is dependent on alternating cycles of wet and dry. If either side of it will be constantly exposed to soil, you might as well use regular mild steel, which is about half the cost of CorTen. https://thecreativeflux.wordpress.com/2015/02/11/what-exactly-is-cor-ten-and-is-it-worth-it/ Be sure to read the links, too!