Yes, we do use concrete. In some cases, it is the most sustainable material. We plan on using these gardens, not just to feed us, but to support the farm for many years. We did try raised beds that were just heaped dirt, with the wind and sun, half the bed would not grow anything. The beds dried out so fast, from the top and the side. When the heavy rains came, the edges crumbled, the mulch wouldn't stay on.... Well, you get the picture. Treated wood is not allowed on the property, except for the occasional gate post. Definitely not in my gardens. To use ordinary wood, would mean replacing it every 5 years. To me, this is hard on the enviroment and my wallet. We went through every option available, but kept coming back to concrete blocks as the longest lasting, able to take a string trimmer, to keep the beds cool, to reduce the amount of irrigation needed, and to all around out last everything else. Sometimes, industrial products are the most sustainable answer.
We do use metal t-posts and metal re-mesh for our trellises. Last year we tried using bamboo. We really hoped it would work, since we have six varieties planted on the property. We did have to replace many of the poles with t-post half way throught the year, they broke. We shall continue to look for alternatives to our metal posts and remesh, but right now, it doesn't look promising.