It is a variation of a persistent gardening myth. Leaving spent flowers in place - not deadheading - provides no measurable winter protection. You can safely remove old flowers whenever they start to irritate you.

Just don't remove too much. Clip off the flowers right where they attach to the stem or you can cut back to the first set of leaf nodes below the flower head. Cutting back any harder could risk the latent flower buds that are now present.

Generally, hydrangeas growing in zone 8 or above never require winter protection :-)

Ah. Ok, good to know I am not crazy.

So what would make someone think leaving them in place would help? I just kept looking at the spent blooms, wondering how they would help as winter protection and I, ???, just came up with ... nothing.

Who knows how any myth gets started? Someone somewhere once upon a time observed that some plants seemed to winter over better or more reliably if left intact until spring. They told their gardening friends and neighbors and then they told others, adding their own spin to the info. Over a period of time, the initial information - which may or may not have been valid to begin with - has morphed into a much broader topic that has little relevance to reality. But it is nonetheless accepted as fact :-) And is often repeated from various sources, including some online and even in a few older extension publications (not necessarily this one but other gardening myths).

But it is not something you will find documented by scientific (horticultural or botanical) sources. And you're correct.....a few wafer-thin, bedraggled flower heads are not going to provide any protection worth noting :-)

The basis for the practice (leaving stems of certain kinds of woody plants uncut until spring) is that cold damage to stems starts at the tips and works its way down. But, yes, we are talking about maybe there being a little more dieback if these stems have been shortened before a cold snap. And if a winter comes along that burns a given shrub down to the snow line leaving the stems long (or with dead flower heads on the ends) will have made little difference.

"But, yes, we are talking about maybe there being a little more dieback if these stems have been shortened before a cold snap."

Would this also apply to just running your hands up the stems to pop the old flower off mid winter/early spring-ish?

I don't cut or really break anything, just slightly tug..

Deadheading should be ok although I find most mophead blooms fall on their own by leaf out time for mopheads or earlier.

When asked, I usually tell new gardeners to leave the old flower buds on as long as they can stand the look. This is an easy answer and where to cut them off in the spring will be obvious - just the dried blossom - and will prevent cutting down too far and losing the flowers following an enthusiasm pruning. I am asked all the time why their hydrangeas don't bloom. In the PNW it is almost always because of incorrect 'pruning'. I tell them 'don't prune your hydrangeas, just snip off the dried blossom!' When I walk in the neighborhood, I am called the Hydrangea Lady. I love it when people excitedly tell me that their plants are finally blooming.