Rosemary and Lavender in Nashville, TN

I live in Nashville, TN, where the summer heat and humidity are beginning to become bothersome. I've managed to grow a rosemary and a "Grosso" lavender in containers outside with an eastern exposure where they get direct sun until midafternoon. They are in quick-draining soil, fed lightly, and watered daily in the evening. Although the top growth is thriving, I can see yellowing leaves at the base of the plants, near the soil. (I've been removing them.) Is this to be expected as the plants grow, or is something wrong? How can it be corrected or prevented?

If the conditions outside are much different from those the plants experienced before being put outside then the old leaves will not have thick enough cuticles to survive outside and will fall off. If the plant has been outside for a long time already and has grown these leaves outside then it may have trouble taking up enough water to keep up with transpiration and is therefore dropping leaves to cut down on water loss. Also the soil could be getting so hot, that the reflected heat is dessicating the lower leaves. For the last two scenarios a heavy mulch would be a big help.
When you do water make sure you water heavily to encourage deep rooting. A bit of high shade would also reduce the stress on the plants.