I am also in North Carolina but in zone 7b. You can get sandy loam and build raised beds from 8 to 16 inches on top of red clay and get really good results. I used to take oak leaves (red maple is best) in the autumn and shred them with a lawn mower. These were piled on top in the autumn for a mulch that broke down into humus. If leaves are not available, hardwood bark mulch (not pine, and with no wood fiber) works as well. I use a small amount of slow release fertilizer when planting, and spread more midseason around the base. If you have voles that use mole tunnels, incorporate crushed rock into the soil around the base of the plant for tuberous sages like S. guaranitica

A word of caution: don't set beds near surface rooted trees like red maple. Their greedy roots will invade the bed in 6 months. It's not a good idea to set beds inside the drip line of any tree.

Thanks Rich. Glad I asked, the local garden center's horticulturalist told me to use just sand and gravel in the bed.