Fix a bad viburnum pruning?
Years ago I got three one gallon sized arrowwood viburnums 'Autumn Jazz'. I foolishly planted them based on the information on the tags which said they would be 3'wide x 4-5'tall. After seeing how fast they were growing and learning that they could actually get to be 3 times that size... I decided to move them. I waited until fall to move them, but decided to cut them back a bit so they wouldn't shade nearby plantings...and because I thought it would help with the transplanting later. I cut off maybe one foot from the top. That was a bad idea I think. They responded well to the transplanting in fall, but the top of each stem branched out at the nodes below the cut. All the new top growth is now weak and flops over.
Should I start cutting some of the branches down to the ground to encourage new shoots to come up? Is it best to do no more than 1/3 of the branches this way each year? And should I wait until late winter to do it? They are probably about 4' tall now, although it is hard to tell with all the flopping.
Advice would be very appreciated.