Certified GKH Gardening Expert
Are they getting sufficient water? When temps reach above 85 degrees F they need 4 inches a week. Have they gotten leggy? If so, cut them back by about 1/3. They should resume blooming in a couple weeks.
Review these cultural needs and see if they are being met. I usually supply regular water and a slow-release fertilizer a couple times during the year and they bloom all summer.