A question about big sacaton grass

Last summer, I ordered several collections from Resource Central's Garden in a Box. We dug out the pampas grass that was thriving (and freely self-seeding) in the strip next to our driveway. We replaced it with two giant Sacaton that came with our boxes. We gave it some root stimulator at the time it was planted (and twice in the weeks following).

It has been over a year and the grass is still tiny. It's almost the same size it was when we planted it. Everything I've read said this is a fast-growing plant, but despite my nurturing throughout last summer and this summer, it's not doing much.

If you also planted this, how is yours doing? I've never had it before, so I don't know if this is normal. Like, I know about sleep, creep, leap, but this appears to just be stalled.

Edited to add a link to a photo.