You can use rock, you can use broken concrete pieces, you could simply pile soil up with no sides. I have seen several gardens where they all have been used.

For organic and for eating I wouldn't trust the aggregate that makes up concrete. Lime can leach out of crete walls and actually kill the grass or whatever one is growing next to it.
I personally never use walls at all.

I no longer use any kind of border, just carefully mounded soil. With the right amount of organic matter your beds will retain their form without the need for any kind of containment. Stones will work, but they offer shelter for beasties you may not want to welcome, and can be difficult to keep free of weeds. Plenty of people do use concrete and cement products with good effect. If you are set on having walls, and termites are an issue, the new plasticized wood used for building decks is probably the best compromise - it is stable, fairly inert, resistant to insects and wildlife, and easy to work with.

Thanks for all your responses.

As a newbie, I was only using the raised bed option because I dont know what "inorganic" materials exist in my backyard soil. I was planning to build the bed and pour in new soil and use some organic feed.

@bill_me: Regarding using plasticized wood, where can I get those?

satx ... it'scallet TREX and it's available in most homeimprovement 'big box" stores.

Hideously expensive.

I use a the Intensive Garden double dug, mounded bed.
No flat top or sides, no more then 12 inches above ground.
Just like the one in "Getting the Most from Your Garden" by O.G.Magazine.
If I ever build walls for a higher bed then I will use rock or wood.

Since concrete is lime it does stand to reason that lime could leach from concrete, but that is not going to be enough to kill grass, although that can cause problems with Azaleas and Rhododendrons. For some people a raised bed is not just a 6 or 12 inch high planting bed but is one 2 to 4 feet high which may well require some kind of sides. Some raised beds, for wheelchair bound users, are around 3 feet off the ground with 6 to 8 inches of soil and nothing except support legs between the base of the bed and the ground. Some botanical gardens have used broken concrete to hold berms and raised beds in place with no adverse affects.

That's a good point by kimmsr. If I were to build raised beds, they would be made of borders that I could sit on, comfortably. That would be about half the space of the garden taken up by paths and walls.
What are the chances of heavy metals leaching out of the concrete?

Concrete blocks?
Ask Jon E Hughes:

Here is a link that might be useful: Ask Jon

" Lime can leach out of crete walls and actually kill the grass or whatever one is growing next to it. "

Hyperbole, I think. Yes, concrete has calcium carbonate in it, which at the slow leaching rate from concrete would be a helpful thing for most soils. Concrete also has calcium sulfate in it, and various alumino-silicates, all of which can be fertilizers and all of which if they leach from concrete would be at a slow rate. If one looks around one will notice that grass and weeds are generally growing more vigorously around concrete, metal poles, even asphalt because of the various fertilizers that are slowly leaching out.

regarding trex. check your local HD, mine has it on clearance. still spendy but 12$ for an 8ft board isnt terrible

Trex, and some other proprietary "plasticized wood" products, may seem expensive, but if you need to replace your wooden frame with any regularity, it becomes more affordable. It is not hard to find off-cuts from some contractors, which can be cobbled together into very workable beds.

Concrete blocks are a good price for how long they last. Longer than the gardener, most likely. It is easy to dry stack the blocks, 8-inch blocks can go three high without moving too much, then fill them with sand. Halfway up when filling put some bags of post-set in if you want to make it a bit more stable. get two-hole blocks if you can (as opposed to three-hole) and then the holes line up and makes it much easier to fill.

I've got azaleas and rhododendrons absolutely thriving around my concrete foundation (and, bright blue hydrangeas)... why would it be different with concrete in a raised bed wall? I'm guessing not enough lime leaches out to create a problem.

Some of us know, because we have seen it and tested for it, that planting beds surrounded by concrete can see an increase in soil pH due to lime from the concrete. This may be from acid rain, the concrete not curing properly, or some of both.
Will this be a major problem? Only if the gardener does not recognize the potential exists and is prepared for solving that problem.

I'm glad to hear the experiences of others regarding cement blocks. My fears were likely unfounded. :)

I did an experiment with a concrete block bed, and after two seasons, I disassembled it and went back to wood beds. Nothing seemed to grow well in them. I didn't think about the PH but the fact that they seem to get very hot from the concrete, which is fine in the spring, but in the height of summer, not so much.

A problem with raised beds in general. The fad is now all the rage in florida, even, where it is maximally unhelpful.

I had to scroll up to see where i was.
Is trex considered organic? Are they still playing that card?
What percentage of the factory misc ingredients is actually recycled. What is the long term breakdown?
I'm asking because i don't really know. I've not really followed but it seems most are not happy with it and now replacing it? It looks fake. Right behind the plastic tool shed, next to the plastic turtle sand box. And little tykes plastic jungle gym, behind the vinyl siding on the house with a plastic bubbly mailbox. Above ground plastic pool behind a chain-link with plastic strips in green and white with plastic adirondack chairs blown by the wind in a heap stuck in a corner...a storm last year. (an unfortunate driving direction landmark for visitors...
just pass the elementary school, pass the 'plastic house', "its for sale!", on the left....)

Plastics are difficult to avoid. Recycling is certainly the way to look at things available for free. Not sure if i would support purchasing such a thing. It would give me a bit of a shudder having a plastic or composite man-made material in my garden.
If heading for a land-fill i might consider a compost bin. Maybe a flower bed edging somewhere. Base for a potting bench?
I do have a compost bin made out of cinder blocks that were piled in the field when i bought the farm. Its the bin i don't really use. Just a place to stack all the big stuff i have no place for. Next to a big rusty vintage manure spreader that gets the really big stuff.

I would just like to mention that it is entirely unnecessary to purchase new soil to have an organic garden.

~emmers