Wow that is an eye-catching retaining wall. Don't see much of that around here where everything is flat and no rocks -- You'd see more of it in northern jersey and I always think "ooh, rocks and boulders...." It would cost a fortune around here.
So are you looking for ideas of things to plant in the pockets or on top... Or down below? I like the photo Pinksand linked to but you'd have to choose plants that are hardy in your winter.
I'm recalling moss and lichen clinging to rocky cliff sides and accented by scrubby shrubs -- your wall is big enough for that. You could try the moss and lichen milkshake trick in the shadier areas. For larger plants, you could probably stuff some mud in the pockets and encourage desirable plants to grow like a rock garden.
What about something like Arctostaphylos uva-ursi -- I can't remember the common name ...wait maybe it's Bearberry? How about wintergreen? You could try other low growing berry shrubs like maybe upland cranberry, nanny berry (huh, is nanny berry low growing? There's a species that only grows in the northern zones 2-3 or something... Heh, I think I'm thinking of crowberries....)
You could also plant short/compact spring bulbs -- what are hardy in your area? I was thinking of small ones like grape hyacinth, snowdrops, crocus, mini jonquils....
...I wonder if crested iris (Iris cristata) would work.
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