It ought to work fine:
it's the same idea as board & brick bookcases!

You're right:
you'd have to put the cement blocks very close together, & I would put the 2x12s close together as well.

THanks sylvia!

I would consider using recyclable (or not) plastic bottles, etc. in the bottom as most plants don't need that deep of a container. This will save you soil and will also save weight. You should be able to put them on shelves of some kind with lots of support.

Just a thought: what about hay bales? They are higher than blocks, and if you don't like where they are, they are not as heavy (although clumsier) as the bricks. In a couple of years they can go on the rest of the garden as mulch, helping hubby keep his weeding duties down.

Do you put holes in the bottoms of the containers for drainage
Linda