Mulch does help add an extra element of protection. Hydrangeas need a lot of water (hence the beginning of their name “hydra”). When the ground is frozen, they can’t absorb water. By adding an extra layer of mulch, you insulate the roots and also prevent the wind from causing the water in the ground to evaporate. This also helps keep the weeds down around them which compete for nutrients throughout the season.

They don’t have the ability to put on and take off layers the way we do, so mulch keeps the soil around the roots a steady temperature. This enables the hydrangeas to just be dormant rather than struggle with the fluctuation in temperatures. Early winter (now) is the best time to do this. If you mulch too early, it can cause rotting, disease, or a cozy warm spot for unwanted insects to winter over.

Decorative mulch is pretty, but for the winter a good 6” layer of leaves is best.  By the spring, most of the leaves will decompose and add organic matter to the soil, which is great for all plants. The freeze/thaw cycles can wreak havoc on plants and even pop them right out of the ground!

If your plant is in a windy location, loosely wrap with a couple layers of burlap, making sure to secure it with sturdy twine. 

Another way is making a mulch cage of chicken wire around the plant. Fill the cage with the shredded leaves to a depth of 6 to 12 inches. The chicken wire helps to keep the mulch around the plants throughout the winter. Remove the winter protective mulch from around the plants in the spring for newly planted, smaller specimens.

Scott, 

The smaller the better, because the leaves will break down faster if smaller.  My husband uses his riding mower to mulch our leaves and the product works for my mulching needs.  Good luck protecting your hydrangea, its a beautiful flowering bush.

Scott,

I had to think about this - I think that you can create sufficient mulch by putting dry leaves in a large garbage bag, squeeze out the air then stomp, roll over, or crush with your hands until the leaves are broken down to a size you like; again the smaller the better.  Just keep rolling the bag over as you crush.  The number of leaves you need will depend on the number of plants you are mulching.  A bushel of leaves would more than enough for a small bush.

Your solution was as good as mine.  The purpose of protecting the young plant has been achieved.  Thanks for letting me know about your success.