There is a particular Saturday in late October when the light is good, the ground is soft, and something in you says: right, let's get this lot cut back. I understand the feeling completely. A tidy garden going into winter feels like a tidy desk going into Monday. But a lot of the cutting we do at this time of year is for our own nerves rather than the plants', and some of it quietly removes next summer's flowers before they've even formed.
The thing worth holding in your head is simple: plants that flower on growth they made last year already have their buds in place. Cut those stems off in autumn and you've cut off the flowers. Plants that flower on growth they'll make next spring can be cut hard, but mostly they'd rather you waited until the worst of the cold has passed anyway.
The ones to leave standing
Hydrangeas are the headline case. Those faded, papery mopheads are not a sign of neglect — they're insulation. The spent flower head shelters the fat buds sitting just below it from frost, and removing them in October exposes the very growth you want in July. Leave them on through the winter, enjoy how they look under frost, and cut back to the first strong pair of buds in early spring when you can see what the weather has actually done.
