Drummond phlox js native to Texas, but has been naturalized across the southeastern states. It prefers sandy, moderately acid to neutral soils but will grow in most well drained soils including alkaline types. However, all commercial seed is likely to come from Europe. The instructions to plant as soon as the ground can be worked are intended for areas where the ground freezes. Drummond phlox will germinate best when soil temperatures are between 55º and 65ºF according to Park Seed's book Success With Seeds. The statement that it is not frost hardy should read IMO not frost hardy in northern states. If you plant indoors use individual pots as the plants do not like transplanting.

In Texas, Drummond phlox is planted in late fall. It overwinters low to the ground until spring temperatures warm. It then grows quickly, blooms, and sets seed before hot weather. The fact that it grows freely across zone 8 means it tolerates temperatures in the low teens. Note that most freezes are short, and the ground rarely freezes and never deeply.