We planted 2 rose of Sharon the end of May beginning of June. One is doing great the other not so much. They get the same amount of water and sun and although it buds and flowers… it won’t stand up. Wilted all the time. See pics
It is most likely that your Rose of Sharon is suffering from what is known as “transplant shock” which is quite common with Hibiscus syriacus. Symptoms can go on for a couple of years following planting, and do include wilting as well as reduced plant growth in general. Plants’ root systems are often disrupted when they are potted for sale (i.e., a significant proportion of their roots may be cut) and it could be that your less healthy plant came to you with a less robust root system. Rose of Sharon do best in full sun and in soil with good drainage. They thrive best when their root systems are not in competition with other plants. Although it may be tempting to fertilize, this in itself can cause more stress to a recently transplanted Rose of Sharon. Some gardeners like to stake their young plants gently. You should continue to make sure that your Rose of Sharon is watered well (but not overwatered), perhaps removing the grass that is growing quite close to it if this is what your photo is showing, and amend your soil in the spring with organic matter.
Very best of luck with this lovely plant.