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Pruning shrubs
Shrubs need some pruning every few years. Pruning promotes a more open
plant with abundant flowering. Yearly pruning of some flowering shrubs
promotes more flowers.
Renewal pruning is removing one-third of the oldest
stems by cutting them off as low to the ground as possible. This is
easiest to do in the winter months. Do not remove too many stems or the
shrub will become leggy and the remaining growth will fall over. 
Sometimes, a
shrub needs to be pruned to reduce it's size. Spring blooming shrubs like
lilac and forsythia can be pruned just after blooming. Pruning later in
the season will result in the loss of flower buds for the next year.
Shrubs that bloom later in the summer, such as Bumald and blue-mist
spirea and hydrangea need to be pruned in the early spring. These shrubs
bloom from the current year's growth.
Shearing is faster than hand pruning and gives a very formal
appearance. However, shearing can lead to plant health problems. In leafy
shrubs, shearing results in weak and unnatural growth. In evergreens,
shearing can enhance spider mite and aphid infestations. Do not shear
evergreens in the late fall or winter. The foliage will brown because of
water loss from drying winds.
For more information, see the following Colorado State Extension fact sheet(s).
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