What does it mean to 'cut back' a plant?

What does it mean to 'cut back' a plant?

Tracy DiSabato-Aust (Garden Designer and Author) gives expert video advice on: What is 'pruning'?; What variables are involved in pruning?; How much pruning does a plant need? and more...

We cut back a plant either before flowering, to reduce the need for staking or to delay flowering, or we cut back after flowering to keep a plant nice and full to reduce that hole that sometimes will develop in the centre of many herbaceous perennials.