I’ve had my Blue Oat Grass (Helictotrichon sempervirens) for maybe 6 years now? It’s always been very nice, and blue, and evergreen but has not once flowered. It has moved around the yard a time or two and that may have something to do with it. It hasn’t moved recently and is apparently now well established. It is making its first show a big one too, 30+ gracefully arching flower spikes that catch the light beautifully against when seen against a dark background and move gently in any breeze.
This grass looks best as a specimen, surrounded by lower growing plants where it can be appreciated fully.