Effect of Pruning Time on Bud Formation and Growth in the Following Year for Spiraea Prunifolia (Bridal Wreath)

For Spiraea prunifolia (bridal wreath spirea), we investigated how differences in the timing of pruning affected sprouting, growth, and formation of buds and flowers, by measuring the number of flowers and sprout growth rate in the following year, to determine how long pruning could be delayed. Our results showed that the longer pruning time was delayed after flowering, the greater the number of buds - but the buds tended to be smaller, and both the rate of new branch growth and the new branch length tended to decrease. We concluded that delaying pruning resulted in fewer buds growing into fully-formed branches. We also found that pruning of branches up to about 30 cm long, representing up to two years growth, resulted in more flowers and more growth in remaining branches in the following year. While the best pruning time is just after flowering, we found that pruning time could be delayed up to four weeks after flowering - i.e. until no later than May - without significantly affecting flowering in the following year. These results probably also apply to other roses related to Spiraea Prunifolia (bridal wreath spirea).