see link about rejuvenation pruning of flowering shrubs ...

good luck ....

ken

Here is a link that might be useful: link

how long have they been there? why are they "thin"? are they getting sun and nutrients?

My Diablo gets better and better each year. I've had it 10 years now and its great. I've never pruned to shape it. just dead stuff. In its early years, I was not overly impressed. Love it now.

It would help if we could see a picture.

a top dressing of compost might help too.

I personally would not cut back any existing stems partway. Yes, that may stimulate new growth, but it will change the growth habit. I guess it also depends if you want that arching look or a bushy look. A bushy look could be nice too, just preference I guess.

my guess is.. with the older ones.. the other trees have shaded them ... over the decades.. and now.. a full sun shrub is reaching out for more light ...

and they may struggle.. even with full and proper renovation ... struggle in the sense of looking like a well grown specimen ... its not usual that they would die outright ... [unless the shade is from norway maples.. lol] .... its just that they may not perform to expectation ... and no fert is going to change improper sun ...

who knows.. as noted.. need pic

ken