What Are Chilling Hours And Why Are They Important? 

So What Are Chill Hours?

In Florida, the definition of chill hours is how many hours in a given winter under 45 degrees.   In other states where the ground may freeze during the winter, the definition includes only the hours between 32 and 45 degrees.

And just why are they important?

Deciduous fruit trees like peaches, nectarines, plums and pears need something like a long winter's nap to go dormant enough to produce blossoms in the spring.

Each species or variety has its own requirement of a certain number of chilling hours, when the temperature drops below 45 degrees Fahrenheit.  The chilling hours can be anywhere from just under one hundred to more than a thousand.

So in addition to knowing that the fruit trees you are planting are meant for your climatic zone, you must be certain that you choose varieties that are matched with the number of chilling hours for your area of that zone.

Here in Florida, we need to plant special 'low chill' fruit tree varieties, and they are generally limited to Florida suitability.  Low chill can be defined as anywhere from 100 to 525 chilling hours, making them better for our mild snow-less winters.

For specific information about how many chill hours you get in your zip code, check out this handy tool by Agro-Climate:

The calculator also presents historical chill hours data,  and chill hours to date for each monitoring station.