Perennials are pruned to stimulate new flowers, new green growth and to remove Dead foliage and spent flowers.
The basic types of pruning are deadheading, cutting back, pinching, disbudding, and thinning. 
Deadheading – removing spent flowers to direct energy into promoting new flowers as well as vegetative growth rather than the production of seeds which reduces plant vigour.
Where you dead head depends on the species of plant and the way in which it grows – deadheading to a new bud, a leaf, a lateral flower or to the level of the crown or basal foliage in the case of single stemmed flowers.
If you are trying to promote self-seeding of plants i.e. columbines then the flower heads should not be removed.
Paeony regrowth after pruning 
Pruning or cutting back of foliage  – can help to stimulate dense vegetative growth when done early in the season in the case of some spring flowering perennials or later to help stimulate fresh bushy growth and repeat flowering.
This is usually done after the first flush of flowers. Later pruning can also help time flowering and shorten the height of some perennials as secondary growth in the same season is usually shorter than the initial growth.
  • Remove mulch around plants.
  • Use hedge clippers - leave approximately 5 cm of stems when cutting to the ground in early spring.
  • Water plants well.
  • Add compost and fertiliser.
  • Aerate the soil around the plants.
  • Replace mulch.
  • Water regularly until new growth develops.
  • Cut back again in autumn to remove dead and old growth and flower heads other than from those plants you want to self-seed.
Remove 25% or more of the growth from a Pelargonium
once or twice annually, to keep the plants from spreading too much,
and becoming straggly. 

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