Gladiolas in a narrow space
I'm fixing to build a rain garden and my plan is to border it with 8 inch tall cinder blocks set four inches deep in the ground. The rain garden itself will be level with the bottom of the cinder blocks (four inches below ground level). I wanna plant something in the cinder blocks, and my thought is that, since they are half submerged, they might not be too hot to put glad bulbs in them. I confess, I've never grown gladiolus before, so I don't know if they spread out a lot underground or how this arrangement might appeal or not appeal to them.
I also considered okra in the holes since it can keep growing down into the dirt if it needs to. Then again, maybe I should just plant herbs or portulaca or marigolds?