Hello, I did not know either, but typed the question (without hash symbol) into the search box at top right of the page, and that seemed to work. Was the question re taking cuttings?

Type the question number in the Search box at the top of the page.

The answer was after flowering if Spirea. Can be done in autumn as well. Can be a trim or a number 2 if really having a tidy up. They don't mind really. Bit of gardeners TLC afterwards, then await regrowth.