Rose of Sharon with mixed colors and poor growth
In front of our Eastport house there are 3 rose of Sharon shrubs. They were medium sized when we moved in three years ago. All three used to have white flowers; the two on the end were all white and the middle one has somewhat smaller blossoms with a dark pink center. The one closest to our front door was slower than the other two last year and even slower this year to set flowers and bloom. There are several branches that appear dead. Now that this one is finally blooming it has a mixture of white and magenta blooms. Where do the magenta flowers come from? Also, all 3 plants seem to be determined to reproduce themselves--many,many small seedlings are popping up everywhere. Is there anything I can do to get the one shrub back to all white and what can I do about the dying branches? Thank you in advance.
Chances are, your rose of Sharon in the photo is actually multiple plants rather than a single plant with two different colored flowers. As you have observed, these plants are notorious for re-seeding and putting up sprouts in the area surrounding them.
The only method of control is to continue cutting and removing the sprouts.
It sometimes happens that hybrid plants will 'revert' and display flowers or growth patterns of an ancestor plant, so if you confirm that yours is a single plant, that is probably the reason for the multiple colored flowers.
It is sometimes necessary to remove fully grown plants if they are not controlled when they first appear.