Yes, you can cut off all the dead stems at any time.

Thank you!

Consider leaving it alone if not yet experienced with Big Leaf Hydrangeas in your area. Aim instead to wait until you get a good grasp of when to prune Big Leaf Hydrangea stems safely in spring without accidentally cutting off spring blooms. Generally speaking, in the northern half of the US, prune leafless stems that remain leafless all the way down by the end of the June; or mid-July if near or within Canada. Move these dates back as you become more experienced.

This type of hydrangea is called a Big Leaf Hydrangea (hydrangea macrophylla) and it break dormancy once temperatures are near or above 50° F. But it breaks dormancy in two phases instead of all parts at once. First, only the brand new stems break dormancy and start to grow from the crown/base of the stems. Then separately and up to 1-2 months later in some locations, the old stems break dormancy, leaf out and bloom. At the proper time, only the bud at the tip of the old stems breaks dormancy and leaf out. After a brief delay, the buds lower down the stems break dormancy and leaf out. The bud at the tip of the stem endings is the one that typically blooms; you will notice tiny broccoli heads when it gets ready to bloom.

The spring 2026 flower buds developed as far back as late summer/fall 2025 on the stem endings but they open only now in spring.

It can be difficult to correctly determine which old stems are alive and which are dead by looks alone because they tend to look dead often. Normal stem colors include shades of gray, browns, sandy colors. Some stems may also get dirty in humid areas and appear dried out. If you cut a live stem thinking it was dead, you would lose the spring flower bud so consider avoiding premature pruning. Instead, wait until the end of June in the northern half of the US or wait until mid-July near/within Canada.

Alternatively, you can also do a very careful fingernail scratch test to see if you detect "green" on each of those stems . Scratch until you get to the normally green cambium layer of the stem and if the cambium layer is brown, the stem is dead. Just because a stem is dead does not mean all stem are dead so, it may be easier to just wait a few more weeks before cutting.

Varieties of Big Leaf Hydrangea that produce two flushes of blooms are called rebloomers; the others are non rebloomers. Rebloomers produce one flush in spring as usual. But then they produce a second flush in late summer/fall once the brand new stems that started growing this year get tall enough to trigger flower bud set and immediately bloom. If this is a nonrebloomer, the brand new stems in picture typically will bloom first in spring 2027.

You cannot visually tell which Big Leaf Hydrangea is a rebloomer and which one is not but you can observe its blooming habit.

I so appreciate your detailed response. I will hold off and keep observing. It is challenging as many stems appear dead but as I now know may only be still dormant.

It's the end of May, for heaven's sake!! If those stems have not leafed out yet, they are not going to and you can cut them back as far as you want without concern. There is NO WAY a bigleaf hydrangea (Hydrangea macrophylla) is still dormant at this time of year anywhere in North America!! I live about as far north as one can in the continental US and bigleaf hydrangeas have not been dormant here for months!

There is nothing magical or mysterious about pruning these types of hydrangeas, reblooming or not. Do not prune to size but only remove bare looking stems in late spring if they have not leafed out OR just remove/deadhead old flowerheads if they have. Everything else is immaterial.

Ah, never say never in gardening. Last week, I heard from someone in Illinois whose rebloomer Summer Crush Big Leaf Hydrangea stems finally started to leaf out at the tips.