I've had bridal veil spirea for over 20 years, they are my garden favorite in the spring. They are very hardy and can take a hard pruning. This year I have cut mine back to about a foot. They were over 7' and starting to leaning forwad in an ugly position. After cutting them back this far, they will not bloom this year but will have a very healthy bloom the following year. Again, they are very hardy and can take a heavy pruning. The best pruning times are in the early spring, (this will affect the volume of bloom) and the early autumn. Light pruning can be done through out the year.