You could air layer it as well as ground layer it. There are some nifty devices out there for air layering so no more plastic wrap/tin foil.

Try this site:

Lee Valley Rooter Pot

hcmcdole, thank you so much! The device from Lee Valley is nifty indeed. That might be just the ticket.

What is ground layering?

Ground layering is the method you proposed in your first post. If the branch is supple enough to bend to the ground or the branch is close to the ground then that is a great way to go. My old blue hydrangea at my old house had a lot of ground layered plants without much effort - some did it by themselves while others I placed a brick on top of a branch or two to force contact with the ground.

Normally you can root a hard or soft wood branches by carefully bending them downward and placing a small mound of loose soil or mulch fines to any depth. Doesn't matter, as long as the stem is covered. Rooting happens within a month or two.

Also, as an oak leaf matures it will send shoots out up to a foot+ away. You could dig those up with accompanying roots to start a new plant.

I find it very difficult to bend hard wood on oakleaf hydrangeas though. If the branches are close to the ground and flexible then it should be as easy as a macrophylla. A brick, heavy pot, or stone will suffice to hold it in place as well as mulch.

How long does it take for an oakleaf to start root suckering? My Little Honey did it this year (first year it did) and it is probably 6 years old. The rest are between 1 and 4 years old and I've not seen any root suckers yet.

I really appreciate all your replies. They've been very helpful. I ordered a rooter pot kit from Lee Valley!

The branch in question is already close to the ground with plenty of length. The following photo is from the top and doesn't show the amount of branch available, but the arrow points to the place where it already naturally curves to touch the ground.

Is there a best time of year to do this? All my plants are on drip irrigation and this spot gets no direct water until rain returns, if it ever does. Would I need to keep the spot where it touches the ground moist, or will moisture drawn up within the plant itself suffice?

If I use ground layering, once it develops its own roots, can it be separated from the mother plant, dug up and moved? I have a couple of nearby places that might be better suited, conveniently along the existing drip line.

It is a lot easier to root a branch in the ground than in a rooter pot. You appear to have an ideal location to do that. Some soil moisture is required, not much. When you pull on the end of the branch you can feel if it has rooted. You need not be in a hurry, as it will wait. It is better done while the plant is in the growth cycle, yours looks great. When you are sure of roots, just cut it loose from the mother and plant on its own. Al

Al, thanks for the reply and advice. Do I have to expose any part of the branch, i.e., cut or peel back any of the outer layer?

No, not needed.