Answer: Hibiscus syriacus, or shrub althaea, grows to 10'-12' tall if unpruned. If your plant has gotten out of hand you can prune it back about one-third its size without harming the plant. It's best to prune in late winter. Once you've cut it down to size you can keep your shrub under control if you cut it back each winter, pruning the previous season's growth back to two buds.
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