Chill factor is unique to where you live, and simply describes the number of hours your fruit trees are likely to spend below 7˚C each winter. It’s definitely worth working out the chill factor at your place, because  in order to get good fruit set, specific varieties of fruit trees need to spend the right number of hours at the right temperature each winter. It can also be a useful diagnostic tool if you have a tree that is flowering,  but not fruiting.

Read the article in Winter – Week 12.