The USDA Plant Hardiness zone is a handy reference to the average severity of winter temperatures at a given site. It, of course, has NOTHING to do with summer gardening. Just FYI, last year the USDA updated these zones, taking climate change into account. They are available, by zip code, at https://planthardiness.ars.usda.gov/. Interestingly, that site not only tells you what the current 2023 zone is, but also the zone that predated it. We've talked about that here. Not sure if this has already been reported here, but be aware that the GardenWeb zone finder, at https://www.gardenweb.com/zones still gives you the old values, and doesn't seem to distinguish a and b subzones. While it includes a link to the USDA site, the numbers it gives are the old ones. This is not a major error, but is something that people might want to be aware of.

I should add that you should be careful about how to use these zones. They're more appropriate to annuals than perennials because these are just AVERAGE winter severities. You can, in time, get winter weather that is VASTLY colder than your listed zone. We've had a good example down here in the last two years. We are at zone 9, but we've had two winters where the temperature got down to zone 7. So when you plant a zone 9 tree or shrub here, it'll be dead. If you want something to last a long time, you might shoot for one that can endure a zone or two lower than your listed zone.