Insufficient water at the root - the best time for planting shrubs like these is actually autumn rather than summer, mostly because its very difficult to supply enough water to the rootball when its planted in open ground - it needs a lot more than a canfull every few days if the weather is warm, dry and/or windy. Leave the hose trickling at the base for an hour or two, although your plant looks as if it suffered water shortage a while ago, since there is plenty of new green growth visible.

Hi, welcome to GoY, I agree with Bamboo, but also they may not produce any more new leaves this year, as they're a deciduous shrub, and not put on new growth until next spring, you may also not get any flowers next year, as they flower in spring/early summer, but keep them well watered and the following year they should be fine, Derek.