I've grown plants of many types for more years than I want to admit (the number would show my age) and I just realized there's something about hardiness zones I fail to understand (it might just be my elevator isn't going all the way up right now).
Anyway, I live in zone 7b which I know means it has averaged 0 to 10 degrees F for the winter cold over past years; I get that, and I understand that a zone 8 or 9 plant isn't gonna make it through the winter on its own here. I understand "close" and mulching the daylights out of plants and have been successful many times.
What I realized I DON'T understand is this:
A plant is "rated" for say zone 4-9. But what does the zone 9 at the end mean? I don't recall ever seeing a top end (summer) for zone temps. I could see where a plant native to a zone 4 locale might bake in zone 10 but I haven't ever seen "top" temps/zones. So what am I missing here? And if there IS a top zone number could someone please point this old guy to it? Thanks!
