Well that rather depends on the variety - there are a great number of herbaceous perennials in that category which are hardy, but also a number of annuals.

Some are perennial others are annual, depends which you have.

Snap Bamboo!

Phlox paniculata, the tall ones in flower now, are hardy perennials. So are P. divaricata, and the little mossy ones you get in the spring/early summer, but as said above, there are some annual bedding type ones as well.

Thank you all so much, you are all so kind. Now that I have some names I can look on questions. Breda.

By coincidence, my AG magazine has annual Phlox seeds on the front cover this week! :-))