I have been following your experiment and Glad you got some germination. In South Carolina the plant is apparently native but I don't know that I've ever noticed it. Found this on the Clemson University home gardening site:
Sweetshrub naturally grows as an understory shrub in mixed deciduous forests, along streams and in moist woodlands. Although it is easy to grow and adaptable, it’s ideal growing conditions are similar to those of its native habitats. For best results, plant sweetshrub in moist, well-drained, loamy soil, ideally in dappled or part shade. It is not salt tolerant.
I goes on to say plants grown in full sun will be shorter.
If anyone has too many seedlings I will happily buy or trade for one.
