Yes, you can root cuttings in water. Up to you if you want to plant it and start a whole new one! However, if you do start a new one you should cut the bloom off first and cut the leaves down by about 50% of surface area. You can cut blooms off a plant at any time but rebloom depends on the type of hydrangea you have. What is it, may I ask?

I don't know. We moved into the house and it was here. Comes back every year. Here is a picture I took of the blooms. Maybe you can tell me what I have?

Thanks

As for what kind of Mac, if you don't know, you probably won't. But if you're getting flower heads that large this early in the season, then you'll have a shot at a rebloom before fall hits, if and only if it's a reblooming variety.

By all means, let them root. When the blooms get old, cut them off and keep in water till the roots look pretty strong. At this point you can cut the leaves in half - or not. Then take a container of good potting soil and put the rooted branches into the soil. Put the roots way down in the container, carefully pulling any leaves that will be under the surface of the soil - they may throw more roots anywhere along the stem as well as at the end of the cutting. Be sure to use a dibble - a stick or something to make a hole in the dirt for the cutting. I find that a chop stick or handle of a wooden spoon works just fine. You do not want to poke the cutting into the dirt without making a hole for it or you will wipe all the new soft roots right off the stem! I put a bunch of cuttings in the same container and keep moist - not wet but not dry. This is the tough part and where most are lost. If you want to check if the roots are growing be sure NOT to pull out or push back into the soil. A slight tug that resists you will be enough to let you know that all is well. If you really HAVE to peek - then lift the cutting with a trowel or spoon and check to see that they are not too dry or wet. Give them a couple of months - new leaves will form and you will have new plants for your garden or to give to special people. Pot them into individual containers and they will most likely bloom next year.

Remember that the blooms are blue because of the way the plant has been nourished; if you want to maintain blue blooms, you'll need to plant the hydrangea in acid soil, or feed it with a special acid, blue-enhancer....

Also if you do start new plants the cuttings need bright shade only with no direct sunlight whatsoever. Moist soil, mist the leaves...