Spring Flowering Shrubs After-Bloom Pruning

Some spring-flowering shrubs that may be pruned as soon as flowering is completed, include forsythia, sweet shrub, pearl bush, kerria, mock orange, spirea and weigela. A few flowering trees are also best pruned after flowering. These include golden rain tree, golden chain tree, flowering peach and flowering plum. Evergreen shrubs such as azaleas, rhododendron and mountain laurel seldom need much pruning. As soon as flowers fade, remove flower heads. If heavier pruning is needed to shape the plant, this should also be done as flowers fade.

Azaleas may also be pruned immediately after flowering, but removal of flower heads is not necessary for development of next year's blooms. Most spring-flowering shrubs form their flower buds for next year during late summer. Therefore, good new growth must have developed by that time. Prompt pruning after harvest allows enough time for good shoot growth and flower buds. Not all spring-flowering plants should be pruned at this time. On exception is the flowering quince. It flowers on two-year-old wood. Prune it lightly and regularly during the dormant period of late winter.

Flowering cherry, although it may be pruned after flowering, should not be pruned while it is making its most vigorous growth. Delay pruning until mid-summer, when growth has slowed. It then will be less subject to invasion by insects or diseases. Some of our ornamental trees are classed as bleeders. These include mainly the maples and birches. To prevent excessive sap flow from wounds, these trees should not be pruned in spring or during periods of rapid growth, but in early summer or fall.

A garden shrub that should receive mid-summer pruning is the hydrangea. Cut the flowering branches back to strong non-flowering lateral shoots. The tree type hydrangea needs to have only the old flower heads removed and any light corrective pruning done.

In lilac, remove flower heads after they are done, and remove suckers coming from the base. If top growth is poor, a few vigorous basal shoots may be allowed to develop for eventual replacement of the tops. On grafted plants, make sure basal growth is of the same type as the top.

Flowering shrubs should not be sheared as a hedge. Appearance and flowering is much better when selective pruning is done. Take out the oldest growth which has become less productive. In addition to removing old stems, cut back some of the longest rank growth to give the plant a better shape.

Source:

http://www.extension.umn.edu/distribution/horticulture/DG0628.html