First, some background. When we moved in 8 years ago, our future shade garden was an unsightly slope of not-very-nice grass. Two mature trees, an oak and an alder, did a good job of preventing anything decent from growing around them. Throw in years of topsoil erosion and the reflected heat from the driveway, and you had just about the least likely place to plant a garden.
Some things did survive the Valley of Death, though: most of the hellebores (except Helleborus foetidus, aka "stinking hellebore," which didn't smell but which didn't live either), the aspidistra (ugly but I can't blame the location), and Acanthus "Summer Beauty" (which never gets as grand as it might in a moist spot but which is still very striking, especially when it's not going dormant from the blazing heat). But the real winner of the dry shade contest is the euphorbia robbiae. This guy got the worst seat in the house - smack under the the oak tree. But once established, he began taking over previously abandoned Valley of Death real estate, moving into territory that no sane plant would even consider. Ordinarily I would object, but since not even weeds will grow there, I feel he's doing me a favor.
I learned that improving the soil is a never-ending process. That "dry shade" doesn't mean that you don't need to water, especially in North Carolina. That it's best to start with 3 inch pots when you're planting under trees.
I learned that Lowes' $1.50 top soil is a pretty decent product, far preferable to the clay-in-a-bag that others sell at that price.
I learned that the trunk of a 2004 Hyundai Elantra will hold up to 12 bags of top soil if you load them properly.
I learned that I have no problem spending hundreds of dollars on plants for dry shade but for some reason won't spend more than $1.50 a bag for top soil.
I learned not to spend hundreds of dollars on plants for dry shade.