Park Seed Garden Journal

Every gardener knows in which zone she or he lives and grows. We know which plants we can have and the ones we are gambling with. We know it has something to do with the weather, but rarely have we asked what does it mean that I live in the color orange and my number is 8a?

This brings us to our next Park Seed Blog Question of the Day!:
“How does the USDA determine which zone I’m in?”

I thought I knew this one but once I started discussing it with our horticulturist, I realized I still had a couple more questions.

It’s really simple once you understand. The USDA zones are based on the average minimum temperature for the last hundred years. Each zone represents a span of 10 degrees. For example, places with average minimum temperatures ranging from -10^oF to 0^oF are in USDA zone 6. The distinctions “a” and “b” represent the lowest and highest 5^o in each zone, respectively.

So then I asked, “It doesn’t have anything to do with length of day, seasons, or how hot it gets?”

Nope, the zones determine what plants will survive the winter temperatures in certain areas and nothing else.

“We often recommend that Park Seed customers from Florida or Southern California not buy certain plants because they wouldn’t survive the high temperatures of summer. How we would know that information?

Plant companies with trial gardens, like Park Seed and university extension services constantly monitor things like that. They grow out huge varieties of plants in various extreme climates to see which ones will survive. Sometimes these plants will live through the hot summers, but they might not bloom like they are supposed to.

If you have any questions about how specific plants might fair in your neck of the woods contact your local University Extension. They will have all the information you need. If you’re not sure how to contact them just Google “[your state] university extension”- I tried it for about half of the states just to makes sure it would work.

Park Seed Zone Finder