Deciduous trees and shrubs can be pruned any time during the year, however, it is easier to evaluate the branching structure during the winter months when the plants are dormant. Flowering trees and shrubs should be pruned immediately after flowering.
Evergreen trees and shrubs can be pruned from early spring through July. Pruning later in the season may result in new growth that is easily burned by early frosts.
Ornamental grasses should be cut to 2″-6″ above ground when new growth begins to emerge in late March/early April. Clumps can be reduced in height by half during the winter to improve appearance. Always leave some foliage to protect the roots until early spring.
Deciduous perennial flowers can be cut to the ground after the first frost. New growth will emerge in the spring. Evergreen perennials should be pruned after they have completed flowering.
Many perennial flowers will benefit by removing dead flowers before they set seed. By inhibiting seed production, plants will often produce a second flush of flowers later in the season. With some species, this technique will encourage continuous blooming.
While many perennial flowers can remain undisturbed for years, some varieties need to be divided periodically (every 2 to 5 years). Overcrowded clumps or reduced blooms are signs that it is time to divide.