Rose of Sharon leaf drop
I have three rose of sharon that are very old. They are large (7 feet high). We transplanted them a few years ago and they were mostly doing fine. The past two years, two of them began to show leaves a little late. Once the leaves were in bloom, they appeared normal. All three bloomed flowers beautifully, but then the two that were late seemed a bit faded (while all the while still producing beautiful flowers). I went away this week and when I returned, to my dismay, the leaves had turned a bright yellow and dropped! I had fertilized them and been watering them well. The leaves also seem to have some black spots on them. No evidence of bugs though. Any advice? Help! I don't want to lose them!