This summer was my first summer married and in a new home. My husband and I were new to landscaping/gardening but did a lot to try to beautify our new place. We saw some salvia at our local nursery and bought a bunch of it to plant around a big tree in front of our house (Red, salmon, & white - I think the variety is Splendens). It has thrived all year and is still in constant bloom. It has not been deadheaded, fed, or watered except for what it received from watering the lawn. I love the way it looks and would love to have the salvia growing around the tree again next year. I am confused as to whether this will come back on its own or if I must replant in the spring. I have seen Salvia described as an annual and a perennial. Does that depend on the zone or type or both? If I must plant again can I do it from seeds to so it will be less expensive? If so, when do I plant the seeds?

P.S. I live in zone 6 borderline-A/B

Thank you in advance for your advice:)