Hi, 

Are you having them pruned too late in the spring/early summer? That may be removing the buds that are forming to flower. Alternatively, have you not had the canopies thinned in awhile? That may help to open them up and get some more light in the branches to promote blooming. You would want to do that in the fall after the leaves come off or anytime over the winter would be fine as well. We don't suggest topping the tree either as that can cause stress and invite pests or other health problems. You can review our tree pruning page to understand more

Drought? We had a drought through most of central Maryland last year from spring through fall and even a pretty dry winter and are in a drought again. Have you supplemented irrigation during this time? 

They don't appear to be spindly from shade and look like they are in full sun so it doesn't appear that they are not flowering due to shade. 

Excess nitrogen in the soil? Have you fertilized your lawn repeatedly?

We always suggest getting a soil laboratory test done to see if nutrients or pH (acidity) level is off to cause the plant to not be producing or growing correctly. If it is lacking in a nutrient level it could be effecting the flower production. We can recommend a certain fertilizer based on the report if necessary. 

Let us know if you have further questions or can share more information and we can assist further. 

Emily