Pressure treated wood, the stuff that resists degradation of weathering, is filled with chemicals. It’s literally soaked in chemicals (that’s its job!). And we don’t want that soaking into the soil we’re using to grow food. The same goes for those ‘fun DIY’ gardens where people like to use old railroad ties. Which are soaked in creosote. Which you also don’t want in your soil.
Pressure treated wood has its place. That’s why we used it to build a fence and retaining wall for our non edible garden. With that said, we also took time to line the back of the retaining wall so the soil wouldn’t directly come in contact with the dirt.
The bottom line being, the only wood you should really be using that would last a long time for an edible garden is cedar. That shit is EXPENSIVE. And eventually you do have to replace it. We ended up calculating it out that really buying Corten Steel beds would mean spending less in the long run.
You never need to paint or seal Corten since a stable rust-like look is naturally formed after several years, completely resists corrosion. (the problem with using metal outside) and you never need to worry about rain, snow, humidity etc. It’s completely resistant to frost and cracking that can happen in colder climates.
But after all that practicality…they look amazing. Chris and I describe our backyard as ‘controlled lush’. We like a ton of plants that combine and overlap and grow like crazy, but we also want modern, clean lines. Corten steel was the perfect linear, modern balance to other choices we made in the yard.