Where do you live and how much sun are they getting? Of all the plants in my garden the Hydrangeas are the first to react to not enough water or too much sun. Al

Every third day is probably not enough water for new plants in a droughty area. How long and deeply do you water when you do? What is your soil like?

FWIW, improper watering is the primary cause of new plant failure.

Sounds like too much or not enough-do you water deeply?

I live in south central Arkansas. We are in a drought. I bought 6 and 3 look great blooming, but 3(in the middle) turned brown, the last one was full of blooms. All of my other plants are growing blooming including a little lamb hydrangea. I do have oyster scale. Never had this before, but an horticulturist told me they should not be dead. They are not dead dead. I am treating with Bayer insecticide systemic and spray. Picking off scales as I see them, even in the dirt. I do water deeply, they thought I might need to water daily too. This is the first time I have not made my own soil when I transplanted them from pots. The scale did get on my eastern snowball viburnum, too. I do need a permanent solution before it gets to my other plants and trees. Thank you.

An update; I have dug up the 3 and the others so far are doing well.

"Water deeply" doesn't work with recently installed plants.
The reason: The roots are limited to the rootball.

Check the moisture content of the original soil. Likely they went too dry.

jean001a makes a point that needs reinforcing. When you plant a new container grown plant, ALL the feeder roots are in the root ball. It takes a month or two to grow into the garden soil, even when the ball is loosened when planting. For the first month the water must be applied DIRECTLY to the root ball. Many plants are lost by watering the soil around the plant, which never gets where it is needed. Al

If it is a water issue, I would say too much, but the others are doing fine. I am not use to losing plants to water issues or planting in the heat of the summer. July is when I usually go to KY, take care of my aunt's flower beds, bring home what she does not want, and buy the half dead ones from the garden centers. This is the first time I have used an irrigation line instead of carrying a water hose around. That may be a big issue. But my Little Lamb Hydrangea that is 3 yrs. old is absolutely beautiful. One flower head is over 14 inches long. They are turning pink now. I would recommend it to anyone.