What does pruning actually do to a plant?
It redirects growth rather than simply removing material — and understanding the mechanism is what turns pruning from guesswork into something predictable.
The central principle: apical dominance. The growing tip of a shoot produces auxin, a hormone that travels downwards and suppresses the buds below it. This is why plants grow upward and outward from their tips while lower buds sit dormant. Cut the tip off and you remove the suppression, so those dormant buds activate. One stem becomes several, and the plant gets bushier.
This explains most pruning advice:
Pinching out the tip of a young plant produces a bushy one rather than a leggy single stem.
Cutting back hard produces vigorous regrowth, not a weakened plant — the root system is unchanged and now supports far less top growth, so what does grow, grows strongly. Hard pruning is an invigorating act, which surprises people.
Light pruning produces modest growth; heavy pruning produces a heavy response.
Cut to an outward-facing bud because the new shoot follows that bud's direction, which is how an open-centred shape is built.
What else pruning achieves: removing dead, diseased and crossing wood; improving air movement and reducing fungal disease; controlling size; and balancing growth against fruiting, since a plant putting energy into vegetative growth puts less into fruit.
Why timing matters so much. It follows from where the flowers come from. A shrub flowering on last year's wood — many spring-flowering shrubs — will lose its display if pruned in winter, so prune it straight after flowering. A shrub flowering on this year's growth, like many late-summer ones, should be pruned in late winter so the new growth it makes will flower. This one distinction resolves most pruning confusion.
The practical rules: cut just above a bud, sloping away from it; cut back to a branch or the collar rather than leaving a stub, since stubs die back; use sharp clean tools; and avoid pruning when frost is imminent, which damages fresh cuts.