Rammed earth walls for garden beds?

Hi all, I'm in Central Texas, and I'm thinking about building a raised bed for growing all sorts of edibles. The end goal is actually a pretty large system of growing beds, but first I have a more general question.

When I think about the materials to be used, I'm not sure what's best. Wood will rot and need to be replaced (which could cause the soil inside to spill out), and I don't want to use stone or brick (costs a lot, don't know how to apply mortar, and don't want to dry-stack since I'm in scorpion country). I love the look and concept of rammed earth, but from what I've read here and elsewhere I don't know whether or not it would be an appropriate material. Basically I need something relatively inexpensive, with virtually zero maintenance, and will be extremely long-lasting. Rammed earth seems to fit the bill, but here are my questions.

For example, once I let the walls dry out, will it be okay to fill the beds with 90%+ compostable (moist) material, or would that degrade the walls? These beds would be out in the open, so what protection would they need to be given on the top (and bottom, for that matter) to prevent erosion?

Also, the plan I have is to have some beds be 3 feet high, some 2 feet, and a single one-footer, with the walls about 6 inches thick. Does that even make sense structurally with rammed earth?

Many thanks in advance for your advice!

---Brian

Rammed earth degrades with water exposure. But you are not bearing any weight above it so I don't think you will have as much trouble as long as you don't try to make a pond (keep good drainage). Liming the surfaces would help, as would adding plenty of lime or portland to the mix. But by that point, it is cheaper to learn to mortar concrete blocks.

6" thick is pretty thin for rammed earth. I don't think I could manually ram anything narrower than about a foot. You need that width work the dirt DOWN instead of just out. Hard to explain but you will understand when you try to do it.

Okay, I was a bit concerned that the walls might be too thin. The largest bed I was planning on making would be 6' x 6' x 3' with essentially a hugelkultur approach to the contents. My lot is small, so no pond here. If the cement content would be high enough to really bump up the price, then I think you're right about just switching to a different material.

My fallback plan was to just use boards (pine treated with linseed oil, most likely) with an inner lining of landscaping fabric. Not ideal for what I was wanting (eventual rot, very little thermal mass), but using cement blocks as you mentioned might be a good alternate. I'll look into it.

Thanks!

If you have good mix for rammed earth on-site (no buying clay or sand to even out the mix), you can do a lot for a little outlay of cash--only tools you NEED are a ram ($30 root bar from Lowes/HD or free scrap), forms (cheap for that small), a shovel, and buckets or wheelbarrow. Two-three bags of portland per ton of dirt, is not that much--but there is WAY more dirt in a RE wall than you think as you are turning it into sandstone.

I have been searching for ways to safely do ground-contact rammed earth for a greenhouse project, but have not found anyone that has a good answer. I have found a couple people in India and Africa that claim they can waterproof roofs and walls with natural materials, but not foundations.