Answer: Hibiscus syriacus, also called Shrub Althea or Rose-of-Sharon, is root hardy to -20F. This shrub is valued for the large flowers produced in mid-to late summer when few other shrubs are in bloom. The plant grows in sun or partial shade and in any soil. Rose-of-Sharon grows 8 to 10 feet tall and spreads 6 to 10 feet.
The growth rate ranges from slow to moderate, and
transplanting is easy. The single or double flowers are in
shades of red, pink, white and purple, depending on the
cultivar. Peak bloom takes place in August. Prune in late
winter or early spring. Frequent severe pruning gives fewer
but larger flowers; no or little pruning gives many small
These shrubs can withstand even heavy pruning if necessary, and yours sounds like a candidate for some renewal pruning. The best time to cut it back is in the winter while they are dormant.
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