Right now at Evergreen Nursery we have a big selection of deciduous fruit trees ready for planting. If you’ve considered planting fruit trees, you’ve probably heard the term “chill hours” being tossed about. You know it has something to do with cold weather, which we don’t always get a lot of here in San Diego. How do you know if a fruit tree will produce fruit in your yard?
What exactly are chill hours?
Chill hours are the number of hours a fruit tree spends in cooler temperatures, ranging between 32- and 45-degrees Fahrenheit. The chilling requirement is the minimum number of hours of cold weather the fruit tree requires to blossom and bear fruit. Trees need this time to go dormant and recharge before producing the following year’s harvest. Chilling requirements can be as few as 100 hours, as is the case for some fig varieties like Brown Turkey and Kadota, to nearly 1000 – for example, fruits like Aprium-Leah Cot Apricot and Snow Beauty Peach each need approximately 800 chill hours and are suitable for colder inland areas only. So it’s important to find plants that are a good match for your local climate.
The colder the better, right?
Not necessarily. Chill hours have traditionally been calculated only by the number of hours the temperatures fall below 45 degrees Fahrenheit. However, research indicates that fruit tree chilling doesn’t occur during below freezing temperatures, so calculating chill hours that occur between 32- and 45-degrees Fahrenheit is thought to be a more reliable method.
Isn’t it safest to just plant trees with low chilling requirements?
Obviously if you choose a tree that needs a high number of chill hours and it just doesn’t get cold enough in your area, your tree might not develop fruit. With our moderate climate, it’s tempting to choose only trees that require very low chill hours in order to be sure to reach the requirement. The danger of doing this is that a tree with a low chilling requirement might break dormancy too soon during a warm spell, only to be vulnerable to a later frost. Keep this in mind if you live in an inland area that gets a fair share of freezing temperatures.
But how do you calculate chill hours for your area?
Luckily, you don’t have to! First of all, our selection of trees here at Evergreen Nursery are varieties that have been developed to have lower chill requirements and have proven to be well adapted to our climate. We’re here to help direct you to the ones that will do best in your area. But if you’re curious and want to do some planning ahead, there are some wonderful apps to be found online that will help you estimate your local chill hours. Here are a couple of helpful sites we’ve discovered:
The first thing you’ll need is the station ID for the weather station nearest you. To locate this, go to and zoom in on the map until you find the number for the weather station closest to your location. Click on the number to get the station ID.
With station ID handy, now you’re ready to use an online calculator to determine your area’s chill hour accumulation. Go to and enter the station ID along with the beginning and end dates for the season you want to sample. Hit ‘Calculate Chill,’ and after a few moments you’ll be provided with your area’s estimated number of chill hours for your sample period.
Now it’s time to start planning which of your favorite fruits you’d like to have available in your own back yard! Chilling requirements can vary widely even within fruit types – for instance a Goldmine Nectarine requires 400 chill hours, while a Desert Delight Nectarine requires as little as 100-200 chill hours. There’s a good chance we have a variety of your favorite fruit that will work for you. Check out our Flip Book, to get some ideas, or come on in to Evergreen Nursery and browse our big selection right here!