I kept mine to maybe 5 main branches, the biggest was 3" diam., & trimmed off the lower small branches so I could plant alot of stuff underneath & expose the bark. The wood isn't too hard, so it's easy to cut if the diam is kept manageable. If you trim a side twig all the way back tight to the main branch, most likely it won't sprout at the cut. And the sprouts from the base are soft & easily cut w/ pruners. If it was my shrub, I'd select a 12" area to keep; cut the rest of the area to ground level & cover w/ heavy black plastic, big rocks & mulch, & see what happens. I think these roots go straight down deep - rarely needed supplemental watering. Digging it out could be quite difficult. I'd guess my shrub was 30 years old & the base was only 12" diameter, but it was planted in dry east exposure shade - which probally slowed the spread. It was on the side of our house, arching over the gate into the backyard. The base was 36" from a sidewalk. Between trimmings or when in bloom we'd just duck to avoid getting poked in the eye. I can imagine a front path main entrance location could have been a problem. When in bloom, it would get so heavy w/ all the tiny flowers, the branches would weigh down halfway to the ground. After it bloomed, and all the tiny flowers started to drop, it would look like it was snowing. The layer of fallen flowers was so thick on the ground you couldn't see the sidewalk. It's a bush worth trying to keep!

i am one to usually suggest that shrubs rarely .... if ever need fert ... but you are undergoing extreme rejuvenation pruning.. reducing canopy .. with absolutely NO INSULT to the root mass.. and then equate all success to increased fert ... i am sure it didnt hurt.. but i would suggest that the plants VIGOR is as much.. if not more affected.. by the rejuvenation.. as your feeding it ... there is no answer to who is right.. i just didnt want you ruling out one for the other ... you are basically turning grandpa into a teenage stud.. and it may not have anything to do with what he eats ... its vigor ... the ability to have so much energy.. that he WANTS to go run that mile.. not whether his bones will crack if he hoiks himself off the lazyboy.. lol ... what did you use for fert??? and how heavy ... ekn

You can technically hack away as much of the stems as you want, as long as the stems and leaves remaining (on old or new wood) are healthy, and that there are enough leaves for the plant to continue to nourish itself. Root problems are more apt to cause stems and leaves to die, so if the roots are healthy then the plant up top should also be. On whatever is left, the plants will set buds for winter just like it always did. I would go halfs for now on the old wood, like you said. You can do it anytime, as long as you don't mind losing the existing flowers. There is no finite quantity of old wood you can hack off and have it harm the plant. It definitely makes sense to take a plant that has about five 4-ft tall stems and cut them down to 2ft to begin building a good structure on a new shrub.

It's always going to want to get that tall. Nevertheless, you can hard prune, and then do a light pruning late spring/early summer, before flower buds start forming, if keeping it a certain size is incredibly important to you. Hard pruning will make it stay much narrower, as the new growth tends to shoot nearly straight up. It will also make your panicles larger, as there'll be less of them, but it may make your plant susceptible to flop on those same large panicles - a lot depends on which variety it is. Hard to name the cultivator, as many panicultas are very similar.