ES develops invisible flower buds from the ends of the stems in the Fall where you live. If the stems and flower buds survive winter, they would bloom in the Spring. However, without winter protection, the stems get killed so you get new growth from the crown in Spring. These new stems may produce blooms too but one has to let the stems grow and get larger. Once they are larger, they produce invisible flower buds by the start of summer and then open them mid to late summer. Two probems with this... ES is a large shrub and it may require that these stems get tall enough before they produce flower buds. If this happens late enough in the growing season, winter weather and lack of sunlight can creep in and prevent bloomage in some years. In very northern locations, I would try a Together & Ever Series or a Let's Dance Series rebloomer instead as they appear to have less issues.. Let's Dance rebloomers bloom in the Spring in southern locations and rebloom in the summer... just like ES but.... these shrubs are not tall tall and tend to be more successful per some of the growers I have contacted in Chicago, nnortheast. Regardless, ES m-a-y still work; there is one way to find out. Just try and see. All you have to do is: keep the area well mulched year around; maintain the soil as evenly moist as you can (meaning no periods of dry soil then wet soil then dry soil again); water when a finger feels dry at a depth of 4"; amend now if your soil is alkaline using garden sulfur or aluminum sulfate; fertilize using 1 cup of organic compost, composted manure or cottonseed meal (or a chemical fertilizer like Osmocote that has a NPK Ratio of around 10-10-10, is general purpose and slow-release).
Pruning: sometime in the Fall -applies only to you-, ES will develop these invisible flower buds to produce spring flowers from. They will stay on and try to open in the Spring. To get bloomage out of them, you will need to winter protect these stems by encasing them with chicken wire, filling the inside with mulch/hay/leaves/etc, topping with cardboard and rocks. Or let the stems die off and get blooms only from the new growth/stems that you are now seeing in the crown or base of the shrub. If you winter protect, you can wait until the end of May-ish to determine if they will leaf out; if they do not leaf out by May to ealy June then prune them all the way to the ground. You can scratch the stems looking for green if you want too. If you winter protect then do not prune in the Fall/Winter/Spring as the flower buds grow at the ends of the stems and you would be cutting the Spring flowers.
In the South, I plant rebloomer hydrangeas in a location where they can attain their estimated size at maturity on the plant label. This way, I will probably not need to prune them ever. Even though my environment is much warmer than yours, we still get some cooler spells in January that, in some years, it will also zap all growth so the shrub has to start again. Micro-climates and protected location can get some hydrangeas above their estimated size at maturity on the label. I have a Nikko Blue that turned out to be a lacecap hydrangea instead; it is now 4-5' (1.2 to 1.5 meters) high, even though there was some winter kill this last winter in some of the other hydrangeas.
The blooms can be kept for winter interest or they can be deadheaded (cut the petiole string the connects the bloom to the end of the stems). I sometimes also put them in the compost pile. Other times, they fall on their own and somehow disappear. I swear I have no idea what happens as I do not see them on the floor. I am not sure if they disintegrate, get reused by other animals or what??? Ha!