Answer: I suppose you could deadhead these and promptly remove the faded flowers, however that would be a huge job requiring a ladder and very few gardeners do it for that reason. You would also lose out on the seedheads as winter decorative feature. Keep in mind you would remove only the faded blooms, you would not want to cut the shrub back at that time as it would stimulate late season growth that would not harden before winter, thus increasing the chance of winter damage. Having said that, I suppose you could try it and see if it makes enough of a difference to be worth the trouble.
Early spring pruning consists of removing winter damage and if needed, pruning to reduce the size of the shrub. If your shrubs typically suffer a lot of winter damage, they may not develop to their full potential. If your shrubs have little winter damage, you might find that a light overall trimming or shearing in the late winter/early spring stimulates branching and causes the shrub to look denser later in the season.
Rose of Sharon will grow best in full sun all day long; in part shade, it will be thin and bloom less.
It also does well in average soil, but you could top dress with good quality compost each year and mulch with several inches of organic mulch year round to help improve the soil slowly over time as it breaks down. You could also apply a general purpose granular or slow release granular fertilizer per the label directions each spring. If the plant is adjacent to a lawn that is already heavily fertilized, you would not need to fertilize the shrub in addition to that.
Although wonderfully drought tolerant once established, an occasional deep watering during extreme dry spells can help this shrub bloom better over a longer period.
Lastly, the overall appearance, shape, size, and quantity, size and quality of the blooms can be affected by which specific cultivar you are growing.
I hope this helps you trouble shoot.
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