If I hadn't seen it created and watched it live through multiple winters, I wouldn't believe that a planting like this could exist in Washington, DC.It's hard enough to keep one lavender alive here more than a couple of years. Much less over 100; they hate this climate and predictably succumb to cold wet clay in the winter. I've found over the hears that the variety 'Provence' which is, from what I can tell, the "production" lavender grown in France. It's fragrant, and has plenty of oils, but wasn't selected for aesthetic traits. I've had one for years in Adelphi, but then our soil is pure sand and gravel.
For this planting at the Herb Garden, they conditioned the soil, inorganically mostly, to a degree that was hard to comprehend, actually resulting in a slight berm. That plus the siting, on that gentle eastern slope seem to have done the trick!