The part that you cannot see is the root system. One shrub may have a larger root system and is better equipped to get soil moisture. The other shrub may have had its root system cut too small and is now stressed more than the other shrub. Feel free to give one more TLC than the other. It is ok for them to wilt so water immediately if the wilting episode looks extreme. Otherwise, water in the morning if it still appears wilted. Most will start to recover by nightfall.

Also, maintain them well mulched (about 4"). I am trying to keep that at least 6" past the drip line over here. If your soil drains well, the extra waterings needed during this dry hot summer will be well received. Give them about 1 gallon to 1.5 gallons per watering during the summers like this one; water the soil/mulch early in the mornings starting with the root ball and moving outwards. Windy locations can promote wilting so use a wind break if the area is windy. Do not fertilize them on their first year; the potting soil mix probably contains those round fertilizer pellets already.

Hydrangeas here are suffering too. With temps in the 105s daily, "everyone" is complaining. I already lost one azalea this summer. How is it going for you?

Luis

Here in Kansas (Zone 6), Nikko Blue cannot tolerate full sun. I had one planted in the shade of a white birch--which suddenly died on me. There was poor Nikko Blue exposed to afternoon sun--and hating it. Always having a wilting problem--it was like there was no way to keep it well watered enough. It survived with the extra waterings for several years, but each year it got smaller and smaller. So I finally moved it to a different part of the yard what is shady. Poor Nikko still has not recovered.

Maybe others have better luck with Nikko, but if yours is like mine, I would say that the sooner you move it too a shadier spot, the better!

Kate

Brutal summer here in Virginia 102 today-lord knows what the heat index was...hydrangeas like nikko will not thrive with afternoon sun-they need mornig sun-after noon shade-they will always struggle with pm sun--move them....

Thanks, all. Good point Luis about the roots. Maybe that explains the difference. Although it has been brutally hot the one is handling it well. My neighbor has some in a similar location but they are older and well established. I will try to baby the one and see what happens. So far I haven't lost anything this year but have two young azalea that are barely holding on.
Oddly, this is the second set of plants I've tried in this location. I had three Shining Sensation weigela that dried out and seemed dead. I pruned all the branches down to 3 or 4 inches and replanted them elsewhere. To my surprise all three are growing! So far the hydrangea are doing better then the weigela, though as I said for one it seems to be much more of a struggle than the other.

I know what you mean. Azaleas are more problematic because their tender tiny fibruous roots grow in the top 4" of the soil. This happens to be an area that dries out fast so they can dry out easily. I already lost one native azalea due to the drought and temperatures. Another one looks like it is suffering so I am having to baby it.