Chill hours calculator
Most fruit trees need a set number of cold hours over winter before they will flower and fruit properly. Enter your ZIP or zone to estimate yours and see what fits.
Chill hours = time between 32 and 45 °F over winter. This is a broad estimate from your zone — coastal, inland and elevation differences are large, so a local station figure (enter it above) is better if you have one.
How this is calculated
“Chill hours” here are the classic model: the number of hours between 32 and 45 °F from roughly November to February. Buds need this cold period to break dormancy evenly in spring — too little and they open late, straggly and unfruitful.
The estimate is derived from your USDA zone, so it is a wide range. Chill varies a lot with elevation and with distance from the coast, so if your county extension or a nearby weather station publishes a local figure, enter it directly.
Chill is necessary but not sufficient — the plant also has to survive your winter low and your summer heat. Always check the variety’s hardiness rating too.