Given the space and constraints available, it may be effective to do the exact opposite of what you are thinking. Instead of planting to add interest in the narrow space, consider a very simple planting of robust, vigorous groundcovers to create a lush yet low-maintenance background. Interest can then be added with planters or other sculptural elements; things that give you a little more flexibility and also control over growing environments.

- Audric

I think too that your solution is to go more formal, more structured, and Audric's solution of containers (or statuary perhaps) is one way to do that.

Conifers are another. Conifers grow up, against gravity, where deciduous and herbaceous plants grow toward the light, and as such when you try to grow them against a wall, they lean out constantly and will just close in on your patio. There are many varieties of upright narrow and dwarf conifers that will lend themselves to growing politely in a narrow space, at least for a good few years, and they can always be replaced. Broad-leaved evergreens such as boxwood and Ilex crenata can also be used in repeats or patterns and will stay in their spots, sometimes with pruning to shape. Topiary, in short, if you enjoy that kind of thing.

The thread linked below has some discussion of and examples of narrow beds.

That said, the layout you describe may not be the best one for the space. If it's possible to redo the layout, perhaps it would be better to put the patio against one wall and create a deeper bed on the side opposite, or patio all around and plants in a corner or something. It's a classic designer challenge to make a small space like that work, and in many books and magazines, and probably all over the net, there are very inspiring examples.

KarinL

Here is a link that might be useful: Narrow beds discussed