impatiens, lobelia, coleus and alyssum .... should all be readily available ...

the issue might end up being keeping the cinderblock damp ... it might tend to wick the moisture from the little pockets of soil ...

good luck ... ken

How about trying a Datura? They like the shade and I think the cinder block will be OK. It is nice to have a different plant when you can. Al

also include Salvia splendens (dwarf varieties), Wishbone flower & wax begonias

I suggest a taller-growing coleus, such as Rainbow Mix. If you buy a market pak of four or six plants, you'll get a nice variety of colors, and they'll look great in your cinder blocks.
Or,if you'd rather have flowers, Super Elfin Impatiens would work very well with the limited light available. You could do all one color (a nice deep pink is called "Lipstick") or you could mix colors.

Both of these grow very well for me in pots where they get just late afternoon sun.

There's not much else, that I know of, that will make a nice show with only late afternoon sun.

Good luck!

PS - Don't forget to pinch, both of these benefit greatly by being pinched back when they're a foot or so high. You get much fuller, bushier plants this way.
Sorry to be always harping on pinching, but it really does make a great difference.
Also, forgot to mention, it pays to fertilize. I use Plant-Tone, and mix in about 2 TBSP when I plant. Then about a month later, sprinkle another 2 TBSP or so on top of the soil around the plant. You could also use Miracle Gro, but I've found the Plant Tone easier and it gets good results.

I've been growing these two plants for over 20 years and I get many compliments on my big, healthy looking flowers, to which I attribute pinching and fertilizing....and of course the right light conditions.

Novembre

thanks. That rainbow mix is nice.
maybe I'll change my mind about not liking coleus!