Having gotten tired or replacing wood all the time, I decided, last year, to rebuild my herb garden using concrete block. Thought I'd update everyone.
The basic garden is a square, the inside of which is four feet on a side. This, in turn, is subdivided into four 2 x 2 compartments. The bed is two tiers high. Originally I'd planned on building two of these.
You know how sometimes the most obvious thing escapes you, then suddenly hits you like a two by twice twixt the eyes? So it was. It suddenly occured to me that the holes in the block were, themselves, containers, and there was no reason not to fill them with soil. Which I did.
Given my location, garden aesthetics are not a particular concern to me. Even so, I wasn't sure I wanted that pile of gray right outside the door. Turns out, however, that you can use a special masonary primer and then any outdoor paint that strikes your fancy. So we painted the whole thing green. Everyone who's seen it pronounces it gorgeous.
What I've got out there are basil, parsley, thyme, and tarragon in the holes. The four big compartments hold lavender, rosemary, sage, and oregano. Mint and chives I left in their own containers.
So, I'm very happy with this approach, and, more than likely, will build a second such bed for the medicinals.
Many of you have asked about container growing, and not having a lot of room. Well, concrete block might be the solution for you. You don't have to build a fancy bed, as I did. Just think of each block as a double pot, each of which holds two plants. You can move them around at will. Or even build a wall, permanent or not. For instance, looking at how my box turned out, I wouldn't hesitate to put an herb wall at the edge of a patio or terrace.