I'm not sure where you got your info from but Festuca glauca is a clumping grass and IME it remains as a clump - not a spreader in any sense of the word. Clumps of most common cultivars tend to be quite compact - mature ones perhaps as much as a foot across, usually a bit smaller, and only 6-10" tall. A cool season grass, it sulks a bit in hot summers and is not considered particularly longlived. A good shearing in early spring generally improves appearance

Do not plant it in the container as it will become root bound. This plant does not do well in poor draining soil from what I have read. Like lol I hear it is not long lived.

One alternative may be Blue oat grass, but I am talking out of my "zone." Look into japanese bloodgrass also, it has some very nice red color, awesome when back lit by the sun!

Last, I would recommend getting a book on grasses from your library, or better yet buying a book by Richard Darke on grasses. It is well worth the cost. Best book on grasses I have seen. Sorry, the name of the book escapes me now. As far as I know he has only written one. Best wishes!

The Color Encyclopedia of Ornamental Grasses.

His other grass book is called Timber Press Pocket Guide to Ornamental Grasses. Obviously this second book is not the full version of the first but it is a very handy book to have at the office, in the car or just sitting handily in arms reach by your favorite chair.

I also have seven other ornamental grass books to choose from plus several guides from different universities that have "hort" classes and that publish papers and guides and recommendation of native grass selections in the states these schools are located. But, that's another story.

Jake