If the plant blooms after June 15th in Northern Illinois, prune after several good freezes but before bud swell in the the spring. If they bloom before June 15th, either prune within the 2weeks after they are done flowering for maximum flowers the next year or prune during the winter which gives the plant maximum health but reduces spring flowering. Plants are either cut off entirely every 5 to 8 years (small twiggy shrubs like the Anthony Waterer spireas) or they are thinned by 1/4 of the stems (remove only the biggest ones)every year. Either cut stems about 6 to 8 inches above ground so new shoots come off the stumps (plant stays narrower but is more disease and insect prone - Hort method) or prune 1 to 3 inches above the ground. ( disease and insect protection way but shoots come from roots so plant spreads wider.)
