Hello, Operaghost. A small/limited amount of wilting has happened to me before and I never found an obvious cause. I first looked for borer insects but found no evidence so I finally assumed it was caused by a windy day. The problem "went away" on its own after a few days or so.

Wilting/drooping of leaves indicates that the leaves are loosing moisture faster than the roots can absorb them. So lack of moisture, a windy day or placing the shrub in a windy location will cause this wilted look. It is very common during summer time on many hydrangeas. But most wilting episodes involve almost the whole shrub, not just 2-3 leaves.

If the wilting episode looks extreme, water � gallon of water immediately and ask questions later. Otherwise, insert a finger into the soil to a depth of 4" and if it feels almost dry or dry then water 1/2 gallon. If the soil feels moist or wet, do not water ..... instead, check the hydrangea again in the morning. If still wilted in the morning, water 1/2 gallon.

You can use the finger method in order to determine when to water. Check the moisture daily for two weeks. For a "new" hydrangea, water 1 gallon of water if it feels dry or almost dry. Each time that you water, make an entry in a wall calendar. After two weeks, review your calendar notes and determine how often you are watering (once every two/three/four/etc days for example). Then set your sprinkler to water 1 gallon of water on the same frequency. If temperatures change 10-15 degrees and stay there, re-check using the finger method for another two weeks.

Wilting can also be a sign that the roots are rotting. When the roots rot, the part of the shrub above ground does not get enough moisture and you get wilting of the leaves. It is hard to differentiate by wilting from lack of moisture or wilting due to root rot. That is why it is important not to water too much.

Root rot normally affects the whole shrub or almost the whole thing. Since your problem appears to be limited to just a few leaves, I would monitor the hydrangea and its soil moisture closely. For now, assume it is either too windy or that it needs more moisture; water according to the finger method.

Regarding your other questions/observations, when hydrangeas get insufficient moisture, the leaves brown out starting at the edges of the leaves so again, keep an eye on soil moisture.

Too much sun shows up as complete yellowing of the leaves. They turn all yellow or white-ish. To prevent this, I plant hydrangeas here such that they get shade starting at 11am-12pm.

Hydrangeas are not bothered by too many pests but there will be some that take a bite and move on. As long as the issue is small and limited as you see, I would take no action. But you could release some beneficial organisms like Lady Beetles, etc

Does that help you, Operaghost?
Luis