Are you 'sure' that you planted purple maiden grass and not purple fountain grass??
The only maiden grass that fits that name is Miscanthus purpurescens BUT, it is not purple. Rather it is green for most of the season and then turns a good flame red in the fall.
On the other hand Purple fountain grass will get quite large over one summer, it is purple for the whole summer BUT ~ is not the least bit hardy in your zone.

You're right...I meant fountain grass.
Dang...this was put in by a "professional" landscaper. he should have known this.

Hi mitch,

You can get quarts of it at the big box stores for 5 bucks or so. I love it and wish it were hardy but happily spend a bit each yr. to have it, it's worth it IMO!

Purple fountain grass is grown as an annual in most areas. It isn't winter hardy unless you live in some place like Florida or California. However, as Lucy mentioned, it is easy to find in big box stores these days for $5 or so per plant and grows very fast.

Thanks, everyone. I was going to make the landscaper replace it since there is a 1-year warranty on all the plants, but in light of what I learned here, that would be petty. I'll head out and buy some today.