Mockorange plants bloom on stems that developed the previous year. If you prune before the plant blooms, you will be removing the flower buds. On a newly planted mockorange, wait until the second year to do any major pruning. If you have a well established mockorange shrub, prune out about 1/3 of the old growth each year. Begin your pruning process after your plant has bloomed. This yearly pruning will help keep the plant healthy and vigorous. If you plant has suffered winter dieback, prune only the dead wood and leave everything else intact until right after blooming.