I also would like to hear about the correct soil for planting heaths/heathers.
My "soil" is mostly clay. Could I mix some orchid mix with MG soils? I need to have some drainage! Anne

Obviously too specific a question for most of us. You might ask the same of the folks at Rock Spray Nursery (Cape Cod). It's their busy season, but they might be able to give you an answer.

I too have clay soil, which I amended with lots of peat, mixing it with the clay, to a depth of about 10-12". Good drainage is most important but so is a moisture-retentive soil, which you now no doubt have. If these conditions are met, along with full sun, I suspect your Calluna will thrive.

You're in zone 5 in the Midwest (harsh, drying winter winds), so be sure to protect them come next winter. Plenty of info about that in this forum.

Here is a link that might be useful: Rock Spray

Whoops. I didn't mix with peat. I mixed with compost and some leaf mold. (Peat and clay can congeal, negatively effecting drainage.) Worked great.