I used the pretty much the same mix in Baltimore,MD and here in Ohio. Had at best a 50% survival rate per flask. I started them (kentuckiense, and pubescens) in a protective cold frame before moving them to a raised bench.
I have had good luck with Spaghnum, or bark based mixes (my mix of choice these days). Over the years I have grown many species and hybrids. I grew macrophylla in bark and didn't have any issues.