Many times when making a tree purchase your asked your zone but not the number of growing season days in your location. When you purchase trees such as Hauer pippin apple you frequently see zone hardiness as 5-10 as shown here Heirloom Fruit Trees for Home & Farm-Trees of Antiquity rooted organic . Honeydew melon are notoriously slow to mature ( up to 200+ days) though you can grow those in zone 5. The length of the growing season per state varies as shown here https://www.arcgis.com/home/item.html?id=a35c325d7bf946b1bf038cea9ebbfeeb many people do not realize is not the same as usda zone hardiness http://planthardiness.ars.usda.gov/PHZMWeb/. Hope this helps someone looking to purchase plants or trees this year. The hauer pippin is an apple I’m experimenting with here in Kansas but I’m aware of the risks with not having enough growing season days to ripen it which is why it’s known as the Christmas apple in California. For a tree or seed company selling is their business and the temptation to fudge = more sales. I also want to say I used a tree above as an example which comes from a highly reputable company and I don’t want that message misunderstood.
Very good point. Cold hardiness zones also have nothing to do with maximum summer temperatures. Parts of San Francisco and Las Vegas are both zone 9. But it’s not necessarily the seller’s burden to explain this to the buyer. The buyer needs to understand their local climate and how it impacts plant growth.
Even chill hours vary. (Parts of) Washington, DC and Atlanta are both zone 7b, but DC has colder average winter temps, despite similar ultimate minimums, so DC gets FAR more chill hours.
Also don’t forget that for the same elevation, the lower the USDA zone, the longer the sunshine hours during the summer. So it somehow compensates. This also answers why Alaska can grow some of the giant veggies during their summer months with midnight sun. Alaska receives more sunlight in spring and summer than any other state and many other parts of the world.