Young, not established, just planted. The blooms are not exactly sunburned but the plant is not able to get enough water so it aborts the blooms. Happens a lot, especially with the start of summer. And even more on newly planted shrubbery. I typically give my hydrangeas shade by 11am-12pm. It is possible that yours can handle that in the weaker MD sun IF, as you said, you see other mopheads planted in similar conditions whose blooms look ok. Otherwise, consider providing shade earlier. New hydrangeas sometimes require covering them with a chair or an umbrella in Summer #1 while they get adjusted (it is called transplant shock). I have one getting special shade this year like that. Make sure you use about 1 gallon of water per watering per plant in the Spring and more in the Summer (1.5 or 2gallons); add 50% more to those numbers if your soil is sandy. Water from the crown outwards because they currently have a tiny root system mostly located around the crown. You can water more or more frequently but make sure your soil drains very well first so you do not start getting root rot. Annabelle is more sun tolerant so I am not surprised that it does not have issues... yet. But Summer is long and it may complain in the future since this is its first year too.

Wait until early spring but while the plant is still dormant. Cutting back to a manageable size while dormant will not impeded root development, like it would if you were to do so now.

Thank you everyone for taking the time and care to advise! Though I must say now I'm still a little confused about what to do. :-D I have read online to move plants early enough so that the root system re-establishes itself before winter dormancy, and then other articles about hydrangeas specifically that state one shouldn't move them UNTIL dormancy. That's why I thought I'd ask here. But it seems like there are folks having success either way, so maybe they are hardier (and/or heartier) than I imagine them to be, at least with the right amount of TLC. One other option I have considered is doing something similar to what hyed has done and prune and reshape the hydrangeas under the window, fronting them with some miniature boxwood type shrubs. But I would still have to end up moving two of them (albeit just steps away rather than several yards) because they aren't lined up and are growing out into our very small yard. I also spend almost all of my available time in the back yard gardening and playing with my veggies and flower beds, and really want to keep it that way. So I question how "good" I will be at keeping these shrubs a manageable size if they remain in the front. I really do think they would be great as a screen in the back yard along the fence line between my house and the neighbor's house, so my inclination is to move them and let them do their 10 foot spread with abandon there. One additional question once I've settled on the question of "when or whether" I should move them, is what kind of fertilizer do y'all recommend to help them along? Thanks a million!

It is a panicled hydrangea, Hydrangea paniculata. It would be easier on the plant if you either transplanted it to a larger pot now or just bundled the current pot in something that will hold it together for the move such as packing tape or duct tape. The problem with wrapping the root ball in burlap is that as it gets moved, the root ball is more likely to fall apart unless treated really gently, and with the amount of time and energy you will be spending on the move itself, it is likely to not get as regular watering as usual at some point, and burlap is more likely to wick water away from the soil around the roots than retain moisture. So having it in a pot is likely better, and you can replant either when things settled down after the move in August if it is done blooming, or wait until it has dropped its leaves for the year. If it has been it the pot for any length of time, the second option is probably better so that you can do some work to straighten roots or cut ones that are circling severely to help the long term health of the plant. Be aware that these shrubs can get really large for some cultivars, so plant it in a space that has at least 8’ width.