Well, you will not kill the plant if you prune, say, 1/3 of the stems for example, as nothing happens to the ever important roots but it can mess up blooming big time. You can deadhead the spent flowers at any time but, that is not the same thing as pruning. To make big cutting changes (no more than 1/3 of the plant per year), now that the planta are dormant may be ok.
Warning: without no pics of the other hydrangeas and without pictures of closer and "younger" blooms, you may end cutting off Spring 2021 blooms so, first determine what type of hydrangeas you have (that one and the others). Resist the urge to cut anything; doing nothing is the best course of action. When I moved to my current house, I waited about 1.5 years before pruning any plants. I spent most of the time identifying them (took pictures of foliage and blooms and also observed when and how many times they bloom) and then determining if they need any special care (sun, water, pruning, food, acidity/alkalinity, etc).
The spent blooms on the picture are not too clear and are too far so it is hard to identify the type of hydrangea from that single pic. No comment on the other hydrangeas that were not photographed. If you already remember what the blooms looked like before they turned brown, post new pics or go to the link below to determine what type of hydrangea yours is.
In your neck of the woods, it is very common to see these types of hydrangea: macrophylla, serrata, quercifolia, arborescens and paniculata.
Macrophyllas -a.k.a. French Hydrangea, Big Leaf Hydrangea, Hortensia- are the ones that you often see when you drive through Nantucket, Martha's Vineyard and basically southeast Mass. Examples: Nikko Blue, Endless Summer, etc. These hydrangeas produce the white/pink/purple/blue mophead blooms that make hydrangeas famous. Some varieties also produce lacecap blooms, which resemble a flat bloom (compared to a mophead bloom). There are two flavors of mopheads: rebloomers and once bloomers. Both produce flower buds in late Summer or in the Fall and the flowers open in Spring. These flower buds are invisible but are located at the ends of the stems. Because of that, it is not recommended that you prune them now. The flower buds will open in Spring 2021 and after enjoying them for a few weeks, you can decide what to prune. Rebloomers will bloom once more but later, usually closer to the summer months. While commercial advertising calls them rebloomers, they are not. New stems that start growing in Spring 2021 will develop flower buds as soon as the stem is tall and old enough; then the flower bud open right away. So they tend to bloom a second time from new stems around Summer 2021. The mophead blooms will be round, roundish or look like half a circle. They may need some winter protection in Mass; ask the previous owner if they did anything special. They may be able to also tell you the type of hydrangea that this is.
Ask the previous owner if they did anything special for winter. They may be able to also tell you the type of hydrangea that this is. Most of the time, in mild winters, they will be fine by just maintaining 2-4" of mulch thru or past the drip line (maybe water in dry & mild winters). In zones 6 and colder, they may require winter protection to bloom reliably. If they have been planted where they can attain their estimated size at maturity, they should not need to be pruned unless you want to remove spent flowers (deadheading can be done at any time), unless you want to remove "extra long" stems or unless you need to cut dried out stems that have not leafed out by the end of May.
Serratas -a.k.a. Mountain Hydrangeas- are basically macrophyllas that grow smaller and their Spring blooms occur a little later than most of macrophyllas. In the wild, they grow in mountains so they handle the cold slightly better than macrophyllas do. Aside from that, everything that applies to a macrophylla would apply to a serrata. Most serrata varieties produce lacecap blooms but a significant number produce mophead blooms.
Arborescens -a.k.a. Smooth Hydrangeas- also produce white/pink/green mophead blooms but their blooms open much later, depending on one's location. Example: Annabelle, etc. They do not require much winter protection (but maintain 2-4" of mulch up to or past the drip line) because they develop flower buds around the middle of Spring 2021 and then the blooms immediately open. Usually, the blooms start lime green and then turn white. Extremely winter hardy and they have varieties that have lacecap flowers. These can be pruned after they bloom but not when you are in the Spring months. Some of these varieties tend to have weak stems that flop so they really should not be pruned ever. The older the stem is, the stronger it is.
Paniculatas - a.k.a. Pee Gee Hydrangeas- are also very winter hardy. Example: Bobo, Limelight, Quickfire, etc. In the northeast, some of the Grandiflora varieties get to become the size of small trees. They produce panicle-shaped blooms that start green or white. They do not require much winter protection (but maintain 2-4" of mulch up to or past the drip line) because they develop flower buds around late Spring 2021 or in Summer 2021 and then the blooms immediately open. Some of these varieties tend to flop more than others. For that same reason, it is not recommended that you prune them as older stems will resist flopping. But, you can deadhead the spent blooms at any time. These are probably the most sun tolerant of all hydrangeas.
Quercifolias -a.k.a. Oakleaf Hydrangeas- are easily distinguished because they have leaves that look like red oak -Quercus rubra-leafs. Examples: Ruby Slippers, Munchkin, Alice, Snowflake, etc. They produce flower buds in late Summer or in the Fall and the flowers open in Spring. The flowers are panicle shaped. Should they need pruning for some reason, they can pruned after they bloom but before they develop flower buds for the following year. Very drought and shade tolerant. Has gorgeous fall foliage.
Down here in the south, I resist the urge to add yet another annual chore in the garden to deadhead the spent blooms and I leave them for winter interest (in the rare case when we get some snow). Mother Nature takes care of all deaheading. Macrophylla and Arborescens's spent blooms usually start falling on their own in the first quarter of the year. Paniculatas and Quercifolias tend to produce bigger and heavier blooms so their peduncle lasts longer and the blooms do not fall until it is almost time to bloom again. If I ever want to remove a bloom early for some reason, I will cut the peduncle string that connects the bloom to the stem.
If you want to see pictures of the various types of hydrangea, go here:
There are 5 main types of hydrangeas that you will find in North America. Learn about each type with helpful images. The #1 resource online for Hydrangeas.
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