If I had a greenhouse, I could try to extend the season even more.
With some extra work, you can extend your season in both directions by using row covers, cloches, and other ways to protect your plants. It does take a lot of extra work (using walls-o-water and bubble-wrapped cages, restaking during windstorms, reinforcing the protection for unseasonably cold nights, etc.) and in my climate I can push the tomato harvest maybe a week earlier for every 2-3 weeks earlier that I plant them, so it's not a huge gain. If I had a greenhouse, I could try to extend the season even more.