By Steragram
Pembrokeshire,
United Kingdom 
I have a viburnum opulus (snowball bush) and a Physocarpus diablo which I've been keeping in bounds by periodically removing the tallest branches. But they are both casting too much shade now - what happens if you just shorten the whole bush - I would like to bring them both down to about five feet if it won't damange the structure too much. And advice please?
1 Sep, 2018
Answers
I have a snowball bush (there are pics in my gallery). I tidy it up every fall, leaving a few 'snowballs' to over winter. If you trim the top a little, it will send up suckers from the base and along the main stem in the Spring. Once the suckers have a good start, hack off the top to desired height, then nurture the suckers to form the new bush. It may look a little wonky the first year, but you can shape as it develops & trim the top to maintain the desired height. Same for Physocarpus .
2 Sep, 2018
Its not that snowball bush Bath Quite agree about the one you mean though - it certainly does know how to sucker...Google Viburnum opulus rosea to see what mine is.
Thank you SBG that's a good idea. Will do that with the Viburnum. Not bothered about the Physocarpus flowers though so might even chop it all at once as plants in the rest of the bed are giving up hope!
2 Sep, 2018
I googled Viburnum opulus rosea and it looks very similar to mine except with smaller snowballs. Mine was a large shrub but I'm shaping it into a small tree. Every year I just trim off a few of the lower branches. Good luck
2 Sep, 2018
That will look attractive. Difficult to know where to start as there are so many strong branches coming from just above the ground. Photo please! (but I don't want a tree where mine is.)
2 Sep, 2018
I know you don't want a tree. I'm just saying mine looks different from yours because I've been working on mine, shaping it over the years. Mine is about 20 years old. Where to start. Find 3 of the strongest main stems. It might help to mark them with yellow string or colored tape. Just go to it and cut all the others back, except the three stems you marked. Might be better to wait for leaf drop in the fall. That way you can see what your doing.
OK here is my photo. Scroll down to read all the comments.
http://www.growsonyou.com/photo/slideshow/339995-viburnum-opalus-snowball-bush/member/bathgate
2 Sep, 2018
That looks really lovely! The "snowballs are certainly bigger than mine! I've never seen one done like that before.
2 Sep, 2018
well yes you can prune them but you may forfeit flowers next year. I think I would reduce a 1/3 of each bush but evenly around the bush to maintain the shape. then next year remove another 1/3 etc.
1 Sep, 2018