- Dick Bir of the North Carolina State University Mountain Research & Extension Center says it's easy to know when to prune two types of hydrangeas: the Hydrangea paniculata and the Hydrangea arborescens cultivars. These cultivars include "Brussels lace," "Kyushu," "pee gee," "pee wee," "pink diamond," "unique" and "white moth," "Annabelle" and "hills of snow." All of these varieties of hydrangea grow on new wood and can be pruned in the winter or after the flowers fade in the spring.
- Oak leaf hydrangea, "mophead," "lace cap" and "big leaf" hydrangeas bloom from old wood. To prevent cutting off potential blooms, prune only the dead or oldest wood each year, but no more than a third of the old wood.
- If you have moved into a home with an established hydrangea, identify it by its blooms. If it doesn't bloom in the second season, remove some of the older wood and watch it the next season.
Don't worry if you are unable to identify the hydrangea. Norm Phillips at University of California at Davis Cooperative Extension and Dick Bir suggest that hydrangeas can survive pruning at most stages. Phillips says these bushes don't really need to be pruned unless they are older than five years, they're too large, or dead or damaged stems need to be removed.
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