You can do some pretty serious wacking in the fall
after the blooming is done.

I was hesitant to post to this because, while I had
yellow potentilla bushes, I couldn't find a picture
of a Fruiticosa to compare. Mine were just plain
old potentilla. Anyway, I would trim/prune at least
twice a year, sometimes three times and they would
flower after each pruning (except the last, which
was done after the bushes stopped putting out new
growth.)

Tracey