If the term chill hours is new to you, don’t worry. I find it’s not something many gardeners think about and for the most part is only important when it comes to fruit tree selection. But when it comes to fruit trees, knowing this number is very important. Selecting a variety that is appropriate for the number of chill hours you get where you live can be the difference between getting fruit or not.
In the simplest equation, the term chill hours refers to the number of hours of weather between 32 degrees and 45 degrees (F). The proper number of chill hours is required for fruit trees to produce flowers and subsequently fruit. If a tree does not get the minimum number of chill hours, it may produce flowers at the wrong time or not produce them at all.
Fortunately all the calculating of chill hours is done for us at stations around the county and they look something like this:
- SLO 390 hours
- Nipomo 428 hours
- SLO West 621 hours
- Atascadero 1204 hours
Basically above the grade is high chill or 800 hours and above, SLO is mid-range 400-600, farther south and coastal areas are low chill, 400 or less. Chill hours vary from year to year but the required chill hours for trees is normally stated as a range. If you are close, it normally works. And generally it’s better to be able to provide more chill hours in your range than less of what is required for a particular tree.
You can often find the chill hours required on the tree’s tag. If no hours are listed, an online search should bring them up (Dave Wilson Nursery’s Product Catalog is linked below). Be particularly careful when selecting trees from box stores as they purchase for a larger region than just our area and as you can see above, chill hours vary widely in our county alone.
If you want a quick list of recommended trees for our county, check out the following articles:
Best Fruit Trees for Cold Winter Climates