Cuttings from non-flowering branches, about 6" long, plunged into the soft soil, should result in a rooted cutting within a few weeks. If you see new growth on top (brighter green leaves) you can feel safe that it's rooted.
The only phlox I have ever cut up to move is creeping phlox. Typical tall phlox can be lifted and divided - just break it apart and plant each section where you want it - no challenge there. I do it only after it has bloomed for the year so cut it back to two or three inches to make it less of a hassle.
I'll take more cuttings of the Callicarpa (Beauty Bush) tomorrow to show you how I do it. I've also done it with Crape Myrtle and a zillion hydrangeas...well, less than a zillion...would you believe 200? Yes!
You can grow them in containers--mine seem happier now that they're in the ground but I had a few that I kept in containers for a couple years waiting to find the right spot for them and they were doing OK in the containers. In your area, if you're growing H. macrophylla they're going to be happiest if they have shade at least in the afternoon. Some morning sun is fine, but afternoon sun in warmer climates will tend to fry them. If you've seen people in your area growing them in full sun, they may be a different species (I believe that H. paniculata and H. arborescens are more sun tolerant).
Like you, I've seen hydrangeas in sun and I don't get it either. They do prefer shade. To answer one of your questions about growing hydrangeas in a pot--I have a beautiful hydrangea in a half whiskey barrel on my front porch where it gets morning sun only and it's doing great. I have a good drainage hole in the bottom of the barrel to make sure the roots don't sit in too much moisture and I keep it well mulched.
I have several oak leaf hydrangeas down by our creek that I dug up out of the woods at our hunting camp. At the camp they grow out of the sides of steep banks which is why mine are down by the creek. Our creek is deep but never has a whole lot of water in it except during heavy rains so the soil is poor, mostly dry and hard. I kept the oak leaf hydrangeas well watered for the first couple of years and then left them mostly on their own except for long droughts and they're doing great. They will tolerate some sun but, like the other types, prefer mostly shade. I love the oaks because the flowers dry so well and I use them in flower arrangements. I've been told the other types dry well too but I haven't had the heart to cut any off the one I have on the porch--they look so pretty on the plant. The oaks just get covered up with flowers though so I don't mind taking a few.
I amended the soil for all my hydrangeas with lots of peat moss and cow manure and they love it (even the oak leaf types). Since yours aren't doing very well, if you haven't already, try adding some fertilizer.
Pirl, I think that once you show me how to take cuttings from hydrangeas I'm going to do that little nature area in the woods I've wanted to do for so long. I plan to line the path with hydrangeas!!! My wife would love it.
I have Endless Summer (Hydrangea macrophylla) in a half whiskey barrel and it's doing great. I had another one that I kept the same way but finally after four years moved it to a place in my flowerbed. You're right, I'm sure it is warmer down here so I don't have to bring mine inside for the winter. I keep them on my front porch which faces south but has a full length roof to keep the hot sun off my plants. I keep the hydrangea on the east end so it only gets morning sun. I just move it up next to the front of the house in the winter time so it will be next to the bricks which hold warmth and keep them from getting too cold. I also add an extra layer of mulch for the winter. I have other plants that are more tropical in nature that I put on a table in our garage (in front of a west facing window) for the winter while they are dormant and they always survive so if your climate is too cold for your potted hydrangea you might try that.
Ed - Would you believe I got my C's mixed up (blame the heat) on the way to take cuttings? Here's the hydrangea cuttings. Always take them from a stem that is not in flower - the back of the shrub is an ideal spot.
Take cuttings: since the difference between the nodes vary there is no way I can give you a specific length but 6 to 7" works fine for me. You will want at least one node buried - more success (for me) with two nodes.
Put the cuttings in a soil-less mix and water them. Next you'll put them in a spot where you'll remember to check on them and where it gets only early morning light. (Picture will be after the Crape Myrtle cuttings.)
Take 6" pieces from growth without buds or flowers. I used three pieces with shiny red new growth and removed more than one set of leaves at the top. I also used two cuttings that were all green and on the underside of the tree.
Place in shady spot that will only get morning sun. Check them every two or three days, more often if it's hot.
Here they make their home with other cuttings and plants in Pirl's Day Care Center for plants!
Good luck, Ed.
By the way, I did check the Callicarpa but every single branch is loaded with buds. I took my cuttings as I pruned it in spring - April or May. You'd follow the same directions as for the Crape Myrtles or Hydrangeas.
I have hormone powder but haven't used it for any cuttings yet though I will use it for Rhododendrons.