Am I blessed or cursed? I have no idea that Caryopteris would grow from seeds but looks like my garden is filled with it as well as lavender. Yes, both Caryopteris and Lavender just spread all over my garden like weeds. It's too good to be true but they have flowers and they look like the ones I planted. I should be happy that I have lots of extra plants but boy, I don't want tons of volunteer plants in my garden.
There are three things you can do: dead-heading to prevent development of seeds, mulching to prevent the seeds from sprouting or, if you don't do the first two, pulling the seedlings out.