there are usually a couple of reasons a plant that should be flowering is not. 1) Pruned at the wrong time, removing future flower buds which allows for excessive vegetative growth. Prune right after they are done blooming by removing a portion of the branch into the canopy. this will release new growth that will form flower buds for the following year. Some older wood should also be removed down at the crown to generate new growth there too. 2) the plants are over stimulated with nitrogen fertilizer. Nitrogen forces vegetative growth. Shrubs in lawns will get nitrogen from the lawn fertilizer.
Read all you can on proper pruning for your area of Iowa and contact your local Extension Office for a more local focused response.