When should Rose of Sharron be pruned?

During dormancy and after the bloom is the best time to prune a rose of Sharon bush, but the woody plant in question (Hibiscus syriacus) may be pruned in accordance with the Ginezumi rule of the pruning "d's" -- damaged, diseased, (never been) done, dry, dying.

As long as the cut is not made into wet wood (which encourages canker) and with the provision that cutting during the bloom may affect flowering that year, but not thereafter.