Many perennial plants may be cut back in some way to extend their flowering season or to improve the size or number of their flowers.

Stopping

It is possible to increase the number of flowers on perennial plants that readily produce sideshoots, such as Helen's flower (Helenium) and Black-eyed Susan (Rudbeckia) by 'stopping' or removing the growing tip of each stem. This will also encourage sturdy growth and prevent the plant from becoming straggly.

When the shoots are one third of their final height, pinch out the top 2.5-5 cm (1-2 in) just above a node. If you have a number of the same plants grouped together, try stopping them a few days apart; this will have the effect of producing a longer overall flowering season.

Thinning

Removing weak spindly shoots from herbaceous plants at an early stage of growth will encourage the plant to produce fewer, studier shoots and larger flowers. Thin plants when they no more than a third of their final height by pinching out the weakest shoots at their base. You should aim to cut back approximately one shoot in three. Use this method for perennials such as phlox, delphiniums or asters.

Pruning

Pruning shrubby perennials in the spring will remove all unproductive shoots and encourage the growth of strong shoots that will produce flowers throughout the summer and autumn.

Dead-Heading

Removing faded flowers from perennials can encourage flowering sideshoots to develop, extending the flowering season. On plants such as lupins (Lupinus) and delphiniums, cutting back the stems to the base when the flowers have faded can encourage new shoots to develop, producing another display of flowers later in the season.