Dunno if it helps, but I noticed that direct water during our last heat wave almost killed my english lavander I just put in. I ended up digging a few shallow holes around the root zone of the plant and would fill these with water every 1-2 days depending on the heat. After switching my watering style my plant recovered in the next week from the wilting.
Hopefully that and a little afternoon shade as others suggested will get the job done.
