You can’t just look at the area you live in and match up USDA zones.
Most fruit trees and some berries require a certain number of hours spent between 32 and 45 degrees every winter in order to properly bear fruit.
Without going into specific details horticulturally, if a tree doesn’t get enough chill hours then it won’t bloom, or may bloom but not set fruit. Clearly frustrating when you have to wait a couple years between planting the trees and when you can expect to see a crop.
Most areas of the north will never have an issue with chill hours. This is a good thing from my perspective, since we’re up here!
But if you’re in a southern area, then you’ll need to keep it in mind.
In most cases you can find varieties of a given fruit, say apples, that don’t require quite as many chill hours. So all hope is not lost!
So Just How Do I Figure This Out?
To make thing even more complicated, there’s no clear way to tell how many chill hours you get. As I alluded to before, one of the main models is to count the average number of chill hours between 32 and 45 degrees.
The “original” model was even simpler. How many hours below 45 degrees. Period.
Then there’s the “Utah Method” … talk about complicated:
- 1 hour of chill below 34 F. is worth nothing
- 1 hour at between 35 and 36 F. gets 1/2 a chill hour
- 1 chill hour is given at 37 to 48 F.
- 1 hour between 49 and 54 F gets you only 1/2 a chill hour
- Anything between 55 and 60 F doesn’t get you anything
- 1 hour above 60 is minus one chill hour
So I recommend forgetting about trying to figure it out yourself, and call the folks that know. Your local extension office.
As a side bonus, they can tell you what trees will grow well in your area.