During the hottest summer months, sometimes newly transplanted trees and shrubs just aren't established enough to pump all of the moisture from roots to leaf canopy that they need. Even if you've been watering regularly, the plant may just be unable to keep up with the water transpired from its leaves into the hot, dry air. This is a temporary problem that you shouldn't see repeated next year when the plant is more established. Meanwhile, ease the stress on your dogwood by not only watering deeply once a week, but by sprinkling water over the foliage. Avoid fertilizing until next year, when you might consider fertilizing at half strength in spring OR regular strength in the fall.