I think 11" is more then enough. Many very successfull gardeners do not a raised bed does anything - it is the soil that matters. I have raised beds. You can mound the soil up - it will settle, even after settling if you use 2x12's (11" on side) get the dirt to 10.75" inches at edge then slop up - the center can easily be 4" higher.

Till and fertilize the existing ground, build 11" raised beds and hill center of beds I am sure it will work great!

Thanks, Donald.

I’m not really “ tilling” lije sone are able to do, but you may be encouraging me to do as much pickaxe/ spading- fork groundwork as I can stand, before filling the bed.

And you make a good point about super- filling to the brim and above , and keep topping up.

If you can improve the underlying soil, then an 11" bed should be fine. Hot dry summers with high walls are an invitation to soil overheating, especially if the sun is beating down on those walls. If you can at least perforate the underlying soil with large holes, and shoot compost into the holes, that would suffice. If you're on top of bedrock, that's demolition work. But it you're just on top of chunks of rock, extraction is just a matter of prying and pulling. I have a bed that I'm slowly expanding that is the latter. It's 8 feet wide, and I add two feet of length to it each year. Mostly with shovel, fork, a hammer and a crowbar. That 2x8 feet takes a weekend of work, and I end up carting away five hundred pounds of rocks, mostly limestone/caliche.

Dan, yes, what I have is some kind of dirt, mixed rocks of all sizes , from pebbles , golf ball, baseball & occasional big guy. So when I do pry out a bunch, a significant volume is removed, so that would be replaced by some mix of compost, Supersoil. It’s funny because when I dig a hole for a shrub, I usually have to “ amend” the planting hole significantly because I’ve removed about 50% rocks & 50% native soil!

I have dug into some areas of my yard that are better, maybe clay- y but with more potential when add compost & such, but for this raised bed I have to put it in a specific area that’s in sun & fairly level.

Boy, that sounds like my plot. When the urban landscapers came in sixty years ago, they ran a bulldozer over the rocky ground, dropped a few inches of soil on top, and laid down grass. You stick a shovel or fork in, and surprise, surprise. You can't get down very far.

Since you are in a dry and hot area, I would suggest doing 17" deep. It gives you more room to waffle your plantings and mulch the top of the beds. You might also want to consider setting in ollas while you are building your bed. Waffling and ollas are very old methods of watering that work great for dry gardens. And if you build your bed with some PVC sunk into the corners and in middle spacers as needed- you can use those for watering tubes and also as holes to put in legs. Legs for if you want hoops for shade or other cloth or plastic over the winter if you need greenhouse action. Or to put in some trellis posts if you like.

Another trick you can use if you have a 17" deep is you can hugelkultur the bottom. Fill the bottom 6 inches with chunk wood. It acts as a space filler and also as a sponge to help retain moisture in the bed. It will break down over time.

A higher bed can also help deter some critters from wanting to get into them. Can be a bit easier to garden over from a bending/leaning perspective. Help keep out low growing/seeding weeds and grass clippings.

As I said below, in a hot area, with a deep elevated bed, you won't have live roots close to the sunlit sides. The soil there will be too hot. The soil surface can be 125F, but you don't want those temps in the root zone. You can make a judgement about whether that's OK. I know people down here who use stock tanks for beds, and they are disappointed with the summer survivability of their crops. One possibility for a deep bed, however, is to properly shade the sunlit side. That's a strategy you might want to use. But if you can't excavate six inches under the bed, I guess a taller bed is your only option.

I guess there might not be one “ right” answer. Plus I can’t do a controlled study! It’s not impossible to add an extra board layer, but would be even more expensive that way.

Hard to know how many inches down into the “ real soil” I will get. Six inches would be a max. Also likely T be somewhat uneven. But if I do create even a shallow “ basin” I think there will be some gradual interactions with soil biome & the occasional hardy worm!

I don’t know that I will do any waffle -gardening. I am not sure the soil texture would work for that plus how I plant things and that I expect roots to spread out and intermingle. Interesting to read about that though & consider, thanks.

I have to fence the whole thing for deer. Rabbits don’t seem that interested in combination of 11” rim & fence, though of course small bunnies, rats can get through. And raccoons, unless top is covered, which I’m not planning for now.

Actually, if you just hang a white cloth on the sunlit side, ideally with a thin air layer between it and the wall, that would suffice to keep the wall at air temperature. Just tack it up with spacers underneath. Might be smart to do that for either an 11 or 17 inch wall. Pull it off in the winter if you're trying to keep the soil warm. Now, either 11 or 17 inch walls are sure not going to stop rodents, rabbits, or coons. That's true that some kind of interaction with the soil biome would be healthy!