To avoid cutting out flower buds, prune in late fall or winter. You can prune in summer to control awkward growth if needed, but winter is best. Here is a good link: http://www.sustainablehorticulture.com/mag_grandiflora.htm And from the forums: http://www.botanicalgarden.ubc.ca/forums/showthread.php?t=6162 http://www.botanicalgarden.ubc.ca/forums/showthread.php?t=7144