I have some hyssop too, 3 great big plants as tall as me about. But they don't get much attention. I wonder if the variety matters.
I believe I'm zone 6 but zone 5's boarder is a town or two south of me.
Oh and to anyone in NJ, Camden County area. I visited Springdale Farm Market yesterday. It's in Cherry Hill and sort of an upscale nursery/bakery/rental hall/and cornfield maze in the fall. They have a greenhouse there with a Vitex in full bloom and covered with bees. Mostly bumblebees but it's still something to see. I'm going to call them up later and ask if they wouldn't mind if I brought my camera. I have a Vitex I planted this year and it's about to bloom, but I'm told there's is about 7 years old. They usually charge a $1 more for everything but they have a lot of variety there. I find things I don't normally get at other stores such as Butterfly Weed and Joe Pye Weed. http://www.springdalefarms.com/index.html
Springdale Farm Market
1638 South Springdale Rd
Cherry Hill, NJ 08003-2738
Back to Liatris. I find bees tend to love prairie plants in general. And it's great how little space they take up. I really just planted them in small groups around other plants I had. Last year we had some white ones that the bees didn't touch. Since I've planed more of the pink ones around those and threw in some new soil they're all coming up pink, and the bees are going at them. I wonder why that is.