I'm not familiar with 'Blue Hills,' and can't find any information on it. I've heard of 'Cheyenne,' 'Sioux Blue' and 'Indian Steel' as cultivars of Sorghastrum nutans.

I haven't grown Sorghastrum, but comparing photos of it to Panicum virgatum 'Northwind' shows 'Northwind' to be far more upright in habit, and almost as blue in color as 'Sioux Blue.' I grow 'Northwind' and it's by far the most erect grass I've found.

If you are going to plant a fairly large potted grass, and have at least 6-8 weeks before truly cold weather, you might get away with late summer planting. To be on the safe side, I'd wait for spring.

Sorry, my goof I was thinking Sioux Blue, and typing Blue Hill. I like the upright form of Northwind, but have lost them two winters in a row.

That's a shame about the 'Northwind.' Bluestem.ca rates it for Z4, but either it's a tenuous Z4, or you're in a cold Z4.

Have you tried Calamagrostis x acutiflora 'Karl Foerster?' Foliage is 4' tall, and blooms to 6' and it's very upright. It's rated for Z3.