I have attached an ispirational picture i found on google to explain better. You would have three materials: concrete, a tile that matches the concrete, and a tile that appeals to you. In the pic the wood would be your concrete and you can see how they transition to tile and yet it is a cohesive design. The banding is shown in the tiled area, but it could be used on either side....I hope that explains what I was thinking

Hi Pete. I live in South Carolina with similar soil and climate. I use raised beds 3 feet wide. No structures for the sides. Just plain dirt. If you are going to construct a bed with materials, I suggest you use boards, even though they eventually rot. Seasoned wood may last 5-6 years though. The reason is, when you use 8 x 8 x 16 blocks, you are wasting a full 8 inches of "reach" no matter which side of the bed you work from. This forces you to have a 4 foot wide bed just to have only 32 inches of working soil and it's still too wide to reach the middle easily. I have mostly 3 foot wide beds with 2 foot paths between (32 of these beds!) but I also have 3 large beds that are 4 feet wide. I much prefer the 3 foot beds, and use the 4 foot wide beds only for crops I don't plant to have to work much with, like beans and melons. On your clay question: I've been working with others on gardening with clay for many years. The best ideas are, if you are going to be gardening there for many years, lay out your beds and then, before you put down block/boards or prepare the top soil, move it actually off the bed or otherwise little-by-little, DOUBLE DIG the soil such that you are tilling the clay beneath. Now, before you put the top soil back, dig in some gypsum (buy it fairly cheaply at Lowes). This does many things for your soil, but the most important thing it does is it actually helps loosen the clay particles and invite in air and water. Yep, even in hardpan clay subsoil, it will do this. Plus, it also provides calcium in quantities that your plants need. Plus it will raise the pH, which most certainly will be very low in that clay, such that the aluminum that is also down there would be poisoning the roots that try to go there. Why improve the subsoil? Because if it is healthy, your plants will also send roots down that deep, and be able to get water and nutrients even in a drought when you happen to not be watering enough. And this is something you only do the first time. Never again will you be working the subsoil like this. So it's actually way more important to work with your subsoil than even to build walls around your beds. This is about nutrients and functionality, not esthetics. A little hard work (a tiller will help) and some money put into gypsum will go a long way toward making your garden productive in the future. If all you want is a fun project, just build some beds. If you want a really productive garden that will use less amendments and less water and produce healthier food for a long time though, consider working the sub soil and adding gypsum. Even if you don't ever work the subsoil like I recommend, it pays to add gypsum into your top soil because it slowly leaches downward and will somewhat help your subsoil anyway, eventually! More on gypsum for clay soil Cheers,

Concrete is lime, gypsum, cement, stone and water. It is not uncommon for concrete to release lime into the soil when new, and then much more slowly as the years go by. This could raise the Calcium as well as the ph of the soil next to the concrete. Is this a problem? Maybe if you are growing plants that require acid soil (like strawberries or raspberries) next to the blocks (though that can be mitigated with Sulfur). However, you are only dealing with thin dividers here rather than a concrete slab so any impact should be minimal. Still, this is a good reason to test the ph of your soil so you know what you are starting with.

Definitely line the wood with plastic. It will last longer. I did that with my new raised beds last year even though I built them from 2x6 cedar. If you get very wet weather, you may find the raised beds won’t drain well since they are sitting on concrete. You could elevate them ever so slightly so that the bottom boards are not flush with the concrete and use landscape cloth to contain the soil. You may have a mess on your patio though that you’ll need to hose off. Unless you are growing carrots or daikon radish you may not need 18” - my beds are 12” deep (and nothing I grew last year had roots that went deeper, even my carrots). For the deep rooted veggies, just use some of the deep Rubbermaid totes (drill holes in the bottom) if esthetics are not that important. Or build some deeper large containers from lumber for those so they match your larger beds. My daugher’s 2x4 bed.