Hi Rosa,

First off, this year's weather conditions since May have been pretty hard on a lot of us gardeners. Even plants that have been in the ground for a few years are struggling in the sun/heat/humidity/lack of rain and nights that don't sufficiently cool down.   I don't know what kind of exposure your garden in the photos faces. If it has been getting a lot of sun, this year the bricks could also be radiating additional heat.  On the other hand, if you lack enough light, plants will falter--but I doubt they would just die.

So, we look at soil. Some questions: Did you dig up grass to make the bed or was this an area that was a bed that was cleared of other plants (or weeds) before you planted it in May? Did you add any new soil or amendments like compost first or simply dig into what was already existing there to plant? How deep is the soil before you hit any obstructions?  How is the drainage--does water pool up and dissipate slowly or does it quickly disappear? The quality of your planting bed is pretty important to success for many kinds of annual plants from garden centers.  I can't tell what you have planted other than what looks like vinca which wasn't well drained soil. You have what might be a hosta which do well in a moisture retentive soil and often only part sun or shade. 

When you put in new plants, they do need to acclimate to being transplanted as it is a stress. The soil is firmed around the roots to eliminate air pockets and  kept moist at least as deep as the pot the plant came in and somewhat beyond so that surrounding soils doesn't leach up all the moisture away from your plant. You can't rely on rainfall but need to baby new plants to keep them growing, especially in our currently summer conditions.  The mulch is good to help keep soil surface cooler and to prevent the heat from quickly evaporating , moisture but the soil you plant in should be good.

You could add your soil test in a photo-- as long as it is close enough to read it.