Woodbine,
I am in SC, so we have the heat and boy, do we have humidity.
The most important thing is you ahve to provide excellent drainage for the shrubs.
Add plenty of composted cow maure in the soil before you plant them.
DO NOT use mulch at all.
Only water them when the temps are under 80 degrees so, if you must water them because it has been at least 2 weeks without rain, water them very early in the morning when it is cooler out.
Heat and watering will kill them.
They are very drought tolerant, so let them go without waterining for 12-14 days before hand watering.
Hopefully it will rain.
Mine have grown into small bushes, about 3 feet tall.
Good luck!

I successfully grew lavender in Maryland for years (in Kensington). NEVER fertilize (you'll get more leaves than "flowers") and plant in a raised hill/bed with sand, pea gravel, any dirt mixture that won't hold water. I mulched with gravel as I do here in SC. I can get it to grow here also under these conditions. Prune in early March and enjoy! I had many different varieties, though in Maryland the Spanish Lavender wasn't as cold hardy.

Butterfly4u and Gardenscents,
thank you for your replies.
I am really glad, that you had success and I will try to plant couple of lavender bushes this year, using your
advices.