I installed a privet hedge that is about 125 feet long. It is about 4-yrs old. I spaced each planting about 18 inches apart. Most are growing and maturing well. Some are starting to die off. It seems like the shrubs that are out of the sun didn't grow as well as the ones in the sun. Any reason for the die-off and are these better suited for sunny areas? I live in Wisconsin so the winters are pretty cold.