You could just bury 8x8x16 cinder blocks along the middle to make 8x8 steps. No soil compaction, easy access. Space them 12-18 inches apart so you can get to everything with two feet seated. Ten bucks worth of material and no carpentry.

Should you decide to rearrange things, you can pull them out and space them differently.

I know it's not certain, but I'm concerned about the issue of possible contaminant leeching in cinder blocks (fly ash content) when used near vegetables. I'd debated using them as the walls, maybe with a plastic liner, but for that.

That's a good point. I had forgotten about that. I wonder if there are strategies for sealing them. Certainly you can paint cinderblocks with masonry sealer to make them waterproof. Not clear how long that sealant would survive under soil, though. You can get paving stones made of less questionable stuff, but that'll run you into more expense.

Of course, you could build up larger blocks out of clay brick. A bit of a project, but it would work.

What are commonly referred to as 'cinder blocks' are now commonly made from concrete. If you buy them new from most (if not all) places, they will now be called 'concrete blocks'.

I recently learned that the easiest way to know the difference is by weight. True 'cinder blocks' are a good deal lighter than concrete blocks, and yes they can contain hazardous contaminants.

Some people have reservations about concrete, but that's an entirely different discussion.

I'd read that, too (about them now being concrete blocks), but then also saw this. It doesn't directly address the issue of now-versus-then, but it makes it a concern for me.

That's a very good point and I apologize for using the term "cinder block" which historically has come to be synonymous with concrete blocks (CMUs). But they aren't the same. I have to suspect that if they are sold as CMUs=concrete blocks, they can't be made out of cinder ash and, as noted, cinder blocks are much lighter in weight.

That being said, I'll bet it's impossible to say that concrete blocks won't have any cinders at all in them.

Also it should be noted that concrete blocks are pretty alkaline, and it is recommended that they not be used around or among acid loving plants. Blueberries in concrete blocks aren't a good idea

I think the 2, 4x12' beds would look nicer than one big almost square box. I wouldn't get a delivery of all topsoil. Can you get a 1/2 and 1/2 mix of compost and topsoil? You can maybe lay woodchips down as your path.

Cedar is pricey, but it will give you plenty of use. Year and years.

Looks aren't a worry for me, just accessibility. I was going to get the compost from a local organic farm.

Accessibility would also be better with the 4' raised beds. I think it's worth the little extra effort. Your choice though :-)

Agree with Chris about accessibility being better with individual beds. If you make one giant bed you have to think about not only yourself having access, which probably means a couple steps are needed to get into the garden if the area will be elevated 18 inches. But you also need to think about how you are going to apply various amendments to the soil throughout the year.

Rodney

Definitely would go with 2 beds for accessing throughout the season and 2 ft. between them is hardly enough. I would allow at least enough room to get between beds with a wheelbarrow. Think about it. Do you want to climb onto the bed every time you need to seed, weed, plant, pick or clear beds?

And, as was suggested, start with a mixture of only 50% topsoil. Drainage is especially important if your area is prone to flooding. Depending on those expectations you might limit compost as well.

Further thoughts: I'd forgotten that dimensional lumber isn't actually the stated size. So 2x6s are 1.5x5.5 actual, and 2x8s are 1.5x7.25. If I did three board levels, the true heights would be only 16.5" and 21.75", respectively. And that's just the frame: in none of the raised beds I saw was the soil within 2" of the top.

So, if I used three 2x8s, that would realistically mean a soil depth of about 19" or less.

I've also sort of decided to make it 10x10 (or, two 5x10s) simply because I'll have trouble transporting 2x12s in my car. Ten feet is still tricky but more do-able, even if I'll have to buy/transport in batches. Plus, I was thinking about making an EMT conduit trellis for the tomatoes. Since that's sold in 10' lengths, that would make it almost perfect to affix to the sides with clamps (it would be going onto rebar buried in the ground, but the clamping would be for added stability).

As far as compost goes, does it really need to be 50/50 for the whole depth? I.e., if I'm doing about 18-19", do I do a compost mix all the way down, or just the top half or two-thirds?

On a similar note, I have a pile of sand around already. Should I spread that down for the bottom few inches, to aid in drainage?

Flooding would be coastal--i.e., salt water--meaning that my only chance is to get the beds high enough to avoid it altogether, which is why I'm aiming high. Any really major flooding and I'm screwed (but in such a case I'll have way more to worry about than the vegetable garden).

I have all the wood needed for two 5x10 beds, and "ECO-SAFE Wood Treatment" by Tall Earth, which is supposed to be OK for use around vegetable gardens.

I was planning on doing the corners with 2x4 vertical posts, and add additional posts in the middle lengths. Certainly one midway along the 5' lengths... debating if I should do two evenly spaced along the 10' length. Or maybe just the one, but pound some rebar just outside the middle of the longer sides, pressed up against the wood.