There will a frost tonight and want to know how much of my oregano plant can I harvest?
It is Greek Oregano thus it should come back next year.
You know you probably could extend your oregano season a little by putting a large pot or bucket over your oregano plant for the night.
You can cut the Oregano almost, but not quite, to the ground. In 4b you'll need to cover it with something for the winter.... like the roses.