Much of your plantings energy and preoccupation right now is into root growth and not into producing leaves and flowers which their root systems cannot sustain at this present time. What you are seeing are the plants throwing off what they cannot sustain now. Once the root system below ground becomes full enough your plantings will put their attention and energy into what is above ground and you will see growth again.

Make sure you keep the border well watered, this is not the time of year to be planting shrubs and perennial plants, much better in the autumn when it is not so hot and there is more likelihood of rain.

Yep, most likely water shortage - it takes a while for plants to extend their water seeking roots into the surrounding soil, so up until late autumn, you will have to supply them with what they need. Light rain won't do it either, that won't be enough to penetrate six inches, which is the average depth of a newly planted rootball. The best way to water is with a sprinkler, soaking the area for half an hour to an hour, once a week or every 5 days, twice a week if the weather is very hot and dry, but not more than that. It's better to water less often and thoroughly when you do water to encourage plants to put out deep roots and not surface ones - they head towards a water source, and if that's you coming along every day with a spray gun on the end of a hose wetting the top half inch of soil, that's where they'll head for.