Perennial hibiscus thrive in full sun (6-8 or more hours of direct summer sun) and moist soil. For most of the growing season in 2023, plus this year so far, much of Maryland has experienced drought. Were the plants being watered if the weather stayed dry last fall and this summer? We ask about last year because, even though the plants looked good, they may have entered winter dormancy weakened by drought stress if there were dry spells and the plants were not watered. Is the tree behind the planting taller and fuller now than it was years ago? Perhaps it's shading the area more than it used to, which can deprive sun-loving plants of enough energy for flowering, plus energy for rapid growth. (Limited soil moisture can also slow down growth considerably.)

If sunlight is insufficient, there would be little that can be done except to move the plants to a sunnier location and replace them with a species more tolerant of part shade. If sunlight is not the issue, then monitor the soil for moisture, watering the plants when the soil becomes somewhat dry to the touch around four or five inches deep. (Normally you could check plants closer to six inches deep, but with this plant being so moisture-loving, we don't want it getting as dry between waterings as other species would tolerate.)

Miri