Apparently the foliage is getting wet and this is causing a bad leaf spot infestation. Water the soil and never the leaves to minimize the chances of getting fungal issues on the leaves. To know when to water, inset a finger to a depth of 4" and water if the soil feels dry or almost dry. If you water when the leaves are wilted, there is a danger that you are watering too much. The leaves will wilt/droop when they lose leaf moisture faster than the roots can absorb more water. The internal pressure differential causes the leaves to wilt then. Scenarios that trigger this condition: temperatures above 85F; too much sunlight (aim to give them dappled sun or morning sun until 10-11am; no afternoon or evening sun if possible); hot, drying winds; lack of water or lack of enough water; small root system (new plants) or disturbed roots due to transplants. Wilted plants can be left alone if the soil is sufficiently moist (use the finger method to check); they will perk up at night on their own if the soil has sufficient soil moisture. In the hot summer months, I make a habit to visually use the finger method when I see wilting and I water immediately if the soil feels dry. If the soil is moist, I let them be and I re-check in the morning. Somewhere around 6-8am when I wake up, I see if any is still wilted. If so, they get water. If you water just because they are wilting, you may be watering too much. That can cause leaf and bloom fungal problems (as seen in the picture) and-or root rot (if the soil remains soggy long enough). Watering twice a day can sometimes be done in well draining soils but try not to make a habit of it. In the fall, discard all foliage and blooms in the trash as they will contain lots of fungal spores; do not put them in the compost pile. If you deadhead any blooms now, discard them in the tras too. You can also cut off the worst of the leaves but do not assume you will get new foliage quickly while in the middle of the summer (maybe in the fall or in spring). Water the soil only, from now on instead. If using a sprinkler system, water around 6-8am so the leaves do not spend the night wet. Use clean sanitation practices (discard plant material in the trash if any falls down or is left in the fall; water the soil only; do not overwater; prune leaves so plants do not touch, something that can help increase air flow and reduce humidity, etc.) as best as you can to minimize spreading the fungal infection to other hydrangeas.

Yes, you can grow ES hydrangea in full sun under the right conditions. It is not the summer sun they mind as much as the heat. In direct sun with the heat, they will likely wilt during the day and perk back up in the evening. A little bit of that kind of stress won't hurt them much as long as you are not in drought conditions. The red leaves may be a feature of the particular cultivar you have. Some of them do have a reddish tint to them that can be highlighted due to environmental conditions. Planting any shrub too close to the house is bad form and not a wise move. Limelight is a much larger shrub than an ES hydrangea and not likely to be a good alternative for most foundation plantings. Your biggest problem with a H. macrophylla cultivar in your zone is going to be late spring freezes. If they break dormancy in an early warm spell and then get frozen to the ground, you will lose that year's bloom. They bloom on older wood and don't have enough time to regrow and bloom in one season of growth. In my southern zone 6 that warm then back to freeze cycle is common and H. macrophylla to a large extent have one good bloom year out of four. The key is they cannot get frozen after breaking dormancy in the spring.

I know this is an old post but I am hoping someone reads this! These comments are the first that I am hearing of old wood hydrangeas blooming only at the terminal buds. I am in 7a on the new england coast and everyone has endless summers and nearly everyone seems to prune theirs back quite short at the end of the season for aesthetic reasons. Aside from last year (where we had weird weather) the hydrangeas have been fine. I am so worried now as I have just pruned the dead flowerheads off my hydrangeas… the flower stalks are all quite tall and filled with buds but now I am worried that I inadvertently snipped off the most important flowering bud! Would greatly appreciate any further insight and best practices about this!

I know I have posted pictures of a neighbour's Endless Summer hydrangeas before. They do beautifully and she not 'a gardener' and doesn't do anything special for them. They are in a raised bed on the SE side of her house. They look like this by early July and stay like that for a long time: This is what they looked like on May 20 this year as the foliage was emerging both from the base and at the lower end of the stems (you can see that she prunes them down in the fall, which you aren't supposed to do.... She also doesn't give them any winter protection.): So I'm not sure what she is doing 'right' but she grows them well here in Zone 5(b)!