I started some zinnias from seed over the winter and was so proud when they came up! They are now about 3 feet tall and thriving in my flower border ( I think). This is the first time I have tried them so I wasn't sure what to expect. A few nights ago, I noticed about half of the petals were missing from a lot of the blooms. By morning, the remaining petals were gone and there is now nothing left but the center. Is this normal for zinnias, or is something wrong?
If the petals went through a color change and the center of the zinnia changed shape...I imagine this would be normal. The next phase would be the seeds starting to ripen or whatever they call it.
Assuming that your plants are not diseased, if you will cut off the spent blossoms ('deadhead' them) that will encourage new flowers. The job of the zinnia is to make seed and die. Your job is to make it keep flowering in an attempt to produce seed.