This shrub is grown for its flowers, and without them, the plant is quite ordinary.
This is no reason to panic and discard the shrub.
In most regions where rose of Sharon thrives, the flowers are best in July and August.
Rose of Sharon’s flower is adored by millions, thanks to its bi-coloration and showy stamen.David Beaulieu
This isa plant for full sun.
Alternately, other surrounding plants can be moved or trimmed to improve the sun exposure.
Shade trees, for example, can be trimmed to remove lower branches that shade the plant.
If you spray high, you will drench the flower buds, which invites rot.
Of course, rain will soak the flower beds from overhead, and you have no control over that.
Drought
The problem of drought is the most straightforward issue to correct.
Simply keep your plant adequately watered during the summertime, and make an extra effort during periods of drought.
How much water should you give your rose of Sharon?
The exact amount (and the precise frequency of watering) depends on the conditions.
Gently dig down 6 inches into the soil and feel it with your hand.
The soil should feel neither dry nor soaked, but slightly moist.
Amounts you apply should be modest, as too much phosphorus can stunt the entire plant.
Neem oil or insecticidal soaps are safe ways to combat aphids and other insects.
Fungal problems usually occur because of overhead watering or lack of air circulation.
Pruning the shrub to improve airflow between the branches may help.
Or, use fungicidal powder to combat fungal disease.
