The new soil won't hold the edging in place. You'd need to show a picture of the situation if you want brainstorming.

Yes -- I use them. They're not precisely cheap but if you collect a few over time, you'll have what you need. They do need to be stacked 2 blocks high, I discovered. You can see the start of one bed on my blog, sort of near the bottom. My blog is Alla's Little Acorn at Blogspot, if links don't work right. There's a photo of the first bed in a new spot, and an explanation of why I tried this, and yes indeedy, it does work nicely. http://allalittleacorn.blogspot.com/ Here is a link that might be useful: Alla's Little Acorn

it's past summer, but i'll add my 2 cents, may be for next year will come in handy. how about using cinderblocks or pavers with holes in them to allow for drainage - use them as a bottom layer to support the box. then fit inside window screen netting or perforated metal grid to retain the soil . and then put a layer of argi-cloth, permiable, for drainage. it'll prevent buggies from crowling in thru the bottom too. when soil is on concrete, doesn't it stain it? if you use pavers, the soil will remain cooler too and drainage is much easier.

This is our 3rd season for concrete block square foot beds. We use the heavier (for stability)concrete ones which cost $1.00 apiece last year from a local supplier (Home depot and Lowe's were a little more expensive). First year we made 4x8 beds, 2 blocks high. To get 4x8' interior space it took 40 blocks (seven each end and 13 each side, overlapped). Also used 18 flat blocks to cover the holes at $.70 each, so a 4 by 8 bed was $52.60 total, which was definitely cheaper than plastic wood. You may only need 1 level high, depending on your existing soil. Top flat blocks are nice to sit on and easily removed to plant in holes, stick in a trellis, or set on the ground when muddy. Grew marigolds and herbs successfully in holes. You can carry a few in your car, so just depends on how many you need and how many trips you want to make. Last year we expanded the beds to 4x16 interior so had them delivered. We just hand leveled (well, fairly level!) as we set the blocks ourselves, slow and heavy, but you only have to do it once! Also rolled landscape fabric around the inside edge of bed before filling with dirt, helps keep moisture in. First year filled with bags of compost & topsoil, but last year ordered 'topmix' of mushroom compost, topsoil & sand delivered & shoveled in, mixing in a few big bags of vermiculite from Atwoods. After initial labor it's wonderful to add a little more soil, measure & plant as I'm doing now that our icy winter has finally thawed. I can email photos if interested.