I would move it in the Spring, that way the roots have a chance to get established and you wont get any frost heave issues. To encourage the shrub to produce more flower buds, prune the plant in late winter before it breaks dormancy.

Actually, fall...after the leaves drop...is the best time to move woody plants. Woody plant roots continue to grow until the ground freezes. Keep the soil moist until it is frozen. Moving in the fall gives the plant 2 cool growing seasons (fall & spring) to put down new roots before hot weather arrives.

A spring move would probably work, but you will have to water faithfully...especially during warm spells.

My experience with RoS is that is is only marginally hardy in z4. My plants finally winter killed after about 3 years. That was in an exposed, rural location. A city garden would likely be more protected.

With that said, early spring may be a better time to move it.

I have a hedge of rose of sharon that it took years to establish. Frankly I am too scared to move it, but I would move it early in the spring since it is still blooming in the late summer and fall. A trick that finally got my hedge completely growing was to pick all the buds the first year, so it put more energy into growing. If you move it, I might do that the first year. Good luck.

I planted 3 White Chiffon & 1 Lavender Chiffon ROS in similar sunny exposure - (2 E facing & 2 W Facing) in 2006. 3 did better than the 1 that didn't receive as much sun (my guess). I encaged them last Winter with leaf mulch as it was their 1st season, do I need to keep protecting each year - they have grown quite taller and wont be as easy.

Thanks for the advice on prunning to keep bushier and shorter! <:->Your thoughts will be appreciated <:->