Prevention or control of pests
Thinning stems on mildew-prone perennials can increase the air circulation
around the plant and decrease the incidence of disease. The arrival of pests may
also be discouraged by better air flow. If a perennial has been infected with a
disease or insects, pruning off the damaged foliage and removing it from the
garden can often be an effective method of control and prevention of further
pest invasion.
Enhance the overall appearance (habit) of the plant
Cutting a plant back before it flowers not only creates a more compact plant but
can help shape the plant’s habit. By cutting outer stems lower than inner stems
you can create a more mounded plant and reduce unsightly legginess. Pinching
or cutting back a perennial when it is first planted normally improves its habit.
Physiologically, pinching or cutting back perennials simply breaks the apical
dominance (a condition wherein the terminal or apical bud inhibits the develop-
ment of lateral buds that branch from the side of a shoot). The apical bud (a bud
located at the tip of a stem or branch; terminal bud) usually grows more vigor-
ously than lateral or axillary buds due to the higher concentration of auxin. If the
dominant growing tip is removed, the auxin:cytokinin (growth hormones that
control shoot growth and root formation) ratio is altered in the lateral buds,
promoting their subsequent breaking and growth. Normally 2 branches will
grow from each pinched stem, but sometimes more are produced. If a structured
look is preferred in the garden, you can also shape plants after they bloom into
neat rounded forms. Simply cutting off any deteriorating leaves, stems, or
flowers can improve the overall appearance of a plant.
Such deadheading leaves a
fresh-looking clump of foliage
that contributes to the garden
for the rest of the season.introduction to PruninG 91