Junipers dying for no apparent reason
Two out of four blue star junipers that were planted nest to each other in the fall of 2016 have died this spring (well, I cut back one to about 3/4ths of its previous size). I am guessing too much water is the cause and have removed the drip irrigation lines to these plants for now. I have definitely been watering more this year with the many 90-degree days beginning in May. These Junipers were planted by a landscaper working for the developer, and many of the shrubs they planted are a little too high, as well. Any other reasons they could have died or am I on the right track?
Denver County Colorado
The foliage of overwatered plants usually turns yellow starting low and in the interior and progressing before the plant actually dies and I think you should have noticed similar symptoms on your junipers if the death was due to overwatering.
Sometimes when weather is hot, plants appear parched but, in fact, there is plenty of moisture at the roots. It's always a good idea to check soil moisture before automatically applying more water. Oftentimes drip emitters are placed up close to the trunk upon installation but need to be adjusted after the plant has grown. If that's your situation, I recommend moving the emitters 6-12" away from the crown. The depth of mulch also can be a factor. While mulch is a good thing, if it is too deep, it can retain too much moisture. Plants need oxygen as much as they need water!
Other things that sometimes cause dieback in Junipers are winter desiccation (which would be relative to where in your landscape your plants are located and whether you did any winter watering) and damage from animals like voles who gnaw on branches. In the latter case, we usually see dead branches rather than entire dead plants.