How To: Prune Spring-Flowering Shrubs
Often, landscape crews are sent out to prune all the shrubs in a landscape. The result: All the shrubs are pruned the same regardless of their growth and flowering habits. The timing of pruning can affect how and how much a plant blooms. Deciduous shrubs are divided into several categories depending upon whether they bloom on old wood (one year or older), new wood (current season), both old and new or whether the flowers are insignificant and are not affected by when they are pruned. Shrubs that bloom on old wood have buds that are formed in summer or early fall. These buds are carried over the winter and, if they survive without winter injury, bloom the following spring. Many spring-flowering shrubs, such as lilac, forsythia, pyracantha, mock orange, chokeberry, deutzia, beautybush, azaleas and rhododendrons, viburnum, flowering almond, weigela, winter daphne and some hydrangeas, bloom on old wood. To insure next year's color show, prune with the following in mind:
Identify your blooming shrubs and research whether the buds are formed on new wood, old wood or both. The above list of plants represent only a portion of spring-bloomers in our landscapes.
Hydrangeas are a class unto themselves. The following bloom on old wood: Hydrangea macrophylla (includes Hortensias and Lacecaps) and H. quercifolia. New-wood bloomers include H. paniculata and H. arborescens.
Determine if pruning is needed. For instance, azaleas and rhododendrons will tolerate pruning but, generally, pruning is required only to remove dead or unruly branches.
Look for diseased or dead branches and remove these at the base of the injury. This will allow you to more clearly see the shape of the shrub and determine the number of healthy branches that you can remove and still maintain the integrity of the shrub.
In general, plants produce more flowers on young, vigorous shoots. On multistem shrubs, remove ¼ of the oldest branches at ground level. Not only will this provide more energy (and blooms) on the younger shoots, it will also encourage more young shoots to develop.
Time your pruning to occur no later than 6 to 8 weeks after bloom. This will allow you the shape the plant and control the size, and the plant will have time to produce more vigorous stems on which to form flower buds for next year.
Flowering shrubs that are “hedged out” will eventually decline in number of blooms, and the remaining blooms will occur sporadically on the plant. The hedging process reduces the amount of young, vigorous shoots and, if performed late enough, simply removes the flower buds. To reclaim “hedged out” spring flowering shrubs, remove ¼ of the oldest branches, spaced equally throughout the shrub. This will allow light into the plant, and buds will form more uniformly around it. Allow new growth to develop beyond the hedge height. Repeat the process for 2 to 3 years. Eventually, the shrub will become more freeform and floriferous.
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