I grow lavendar on what I call my hell strip - up both sides of a cement driveway here in the LowCountry of SC.
I add gravel and lime when planting and mulch with light colored sea shells. This allows the sun to reflect back up into the plant, helping to keep the plants dry. Around mid-February, I cut the plants way back. We return to VT for the summer during the month of May. The plants receive no attention after their spring cut back and are in great shape when we return home in October. Have entered cuttings in the fall fair flower show and won blue ribbons.
I've got a plant in the "inferno zone" in a little rock garden between the sidewalk and the road, and it does pretty well there too! I'm glad to know the light colored hard mulch works for you -- I imagine sea shells should be similar in their effects to light colored gravel or sand, and maybe as a bonus they would add just a bit of lime to the soil over time.