Welcome to the forum, deacondog! Somehow it does help to find we're all in the same boat, doesn't it? Many on various forums reporting a variety of well-established plants' top growth killed to the ground even in zones 8 & 9. I'm with SouthCountryGuy, too - don't count 'em out yet. If you give up on the old stems (and for reasons already mentioned, this may be wise at an appropriate time), the root mass still likely to produce new growth in its own good time. Over the years, found many plants left for goners regrew over a year later. (Clematis are infamous for this.) Though I'd grown hydrangeas in other gardens (when they were considered low-maintenance shrubs), overlooked adding them here till last year when the new rebloomers caught my attention. Experimenting, brought in a few mopheads, potted them up, half-plunged the pots in a mound of soil covered with oak leaves last Fall & forgot about them - until the ice & snow storms became monotonous. At that point, imposssible to pry the pots from the frozen ground. If I'd only known what the weather had in mind, they could have safely spent the harsh season in the garage or more thoroughly protected - our common lament. After the Spring freezes, the pots were unearthed & set atop the ground. Only Leuchtfeuer (Firelight, Beacon Light, Lighthouse) has shown any growth - halfhearted, but much appreciated. Like hokierusty in Williamsburg, the temp didn't dip below 0 here, but the extended cold did more damage than short lows below that in previous years. In this on-again, off-again slow motion Spring - almost Summer! - the soil here still hasn't warmed consistently. Well-mulched soil has barely warmed at all. Hydrangeas sited in part shade likely still haven't gotten the grow message in their cooler morning sun spots. Rose growers are finding that pulling mulch away from the root zone for stunted plants has worked to warm the soil & stimulate growth. Tried this for other woody perennials with success this year - latest they've ever emerged by a month at minimum. The principle should apply to planted hydrangeas in conditions like mine, as well, shouldn't it? For the potted hydrangeas, plan to move them to the blacktop driveway where they'll receive the heat sink effect from morning sun (still with afternoon shade) to see if additionally warming their soil will help awaken them.

Nope, not too late. Cut back to 2-3' (some people do it lower) and get rid of extremely thin branches. Should regain most of its size and bloom by sometime in July.

You can of course cut them off now - dead wood can be removed at any time. It's just a lot easier to do so when there are no leaves present so recommend it as an annual practice every spring. There are various methods of winter protection, often involving building some sort of wire cage around the shrub then filling the cage with shredded leaves or straw, etc. It kind of depends on your climate as to how proactive you need to be -- in my climate, winter protection is unnecessary but is usually recommended for at least zone 6 and lower. Virtually all species of hydrangea prefer some shade, typically in the hottest part of the day. Exposure to hot afternoon sun in summer frequently will cause wilting - it's not a nutrient deficiency. Ideally they should be situated where they receive morning sun and afternoon shade but plenty of water can offset the issue as well. The exception are the panicle hydrangea (Hydrangea paniculata), which is much more sun and heat tolerant. Here is a link that might be useful: Hydrangea macrophylla winter care

July 14, 2016, z4: I live in West Central MN, z4, have had an Endless Summer, Twist & Shout, planted on East corner of house since summer of 2011 (5 yrs at time of this writing). It gets full sun in morning, a little dappled sun in afternoon for a very short time, rich soil, moist conditions, landscape fabric covered with wood mulch, no turf or other nearby vegetation to compete with. This should be perfect Hydrangea conditions, and while this plant has been robust and healthy from the very beginning, it does NOT get anywhere near its advertised size. (Label that came on my plant says 4 to 5 ft tall and wide.) It dies back completely to the ground every winter so growth starts all over, from ground level, every spring, rather late in the spring, and reaches its maximum size of 2 ft tall X 3 ft wide in mid July. This also means it blooms only on new growth. Though it's advertised as blooming on both new and old growth, there is no old growth that survives the winter for blooms to grow on. I do not cut it back in the fall....don't touch it at all.....and leave the old growth until the following season. In the spring, I clean up the dead and fallen leaves from the year before but leave the old stems standing. (I started leaving the previous year's dead stems through the following spring beginning from the time I planted it, always hoping that, if given enough time, they'd come to life and be that "old growth" that would give the plant that bigger size and more flowers. I've given up that idea, but it's just a habit now. It's become one of those, "This is how I manage this plant because I know it does no harm" , kind of things.) Once the new growth is nearing the height of the previous year's stems, I simply break the old ones off as close to ground level as I can without disturbing new growth, usually ending up to be 3-4 inches above ground level, completely hidden by the new growth. Because they're "dead", the old stems just snap off by hand, very easily, and those few inches that may be left behind have fallen into the soil by the time late fall arrives and the plant once again goes into dormancy, has shed its summer foliage, and everything that was living that summer dies back completely over the coming winter. Over the summer and early fall, it usually has up to 12 blooms at any given time, depending on how much TLC it gets. Blooms range in size from 3" to 7" across (older blooms). Each flower lasts a long time. As far as the color of the flowers, some years they are more on the purple side, some years they are a bit more pinkish. Most years, there's an interesting mix of both colors on each individual flower, often times starting out more on the pink side but changing to purple with a smattering of pink as the blooms mature to full size. I don't know how the plant determines, but it does so on its own since I do NOT amend the soil with anything to change the PH level or influence the bloom color. All I do as far as feeding is give it a drink of water soluble "Bloom Booster" fertilizer (10-52-10) three or four times during the summer, beginning around July 1 (when the plant is nearing its full size and focusing most of its energy into putting on new blooms), and ending the end of August, at the latest. I tried giving it a balanced fertilizer beginning earlier in the season and found that it there was lots of green but sparse on flowers and could get rather leggy. This feeding routine seems to give the best results, in my situation, anyway. I'm very fortunate to live in an area of glacier-rich black soil (black gold!) where pretty much EVERYTHING I've ever planted in my 40 yrs of gardening/landscaping grows much larger and faster than what's stated on the labels. I was expecting the same with this Hydrangea, that its mature size would be greater than its label indicated, so I gave it plenty of room, which is doesn't come close to filling. I've decided to transplant it either this fall or next spring (depending on what I find on the internet for info on how it will stand up to fall transplanting in my zone, which I've not yet found). I think I'll put a Black Lace Elderberry bush in the vacated spot and move the Twist&Shout Hydrangea further down the east side of the house, next to a large bunch of established White Phlox just about to break into beautiful full bloom this time of year. That's my only disappointment with this Hydrangea, its ultimate size. According to my experience, it will never reach the size stated on the label in zone 4, where it dies back to the ground every winter and comes back from ground level every spring. An attractive and, so far, hardy zone 4 plant, to be sure, but not nearly as large as some other varieties in the Hydrangea family, and the larger size is what I was wanting when I bought the Twist and Shout.