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Growing It Local > Garden Wiki > Chill Hour Calculations

Chill Hour Calculations

Some plant species require a minimum number of chill hours per year to do well. It's important to know the average chill hours for your area when deciding which types and varieties to plant. The local chill hour calculator below will help you determine the chill hours at your location.

Trees that are sensitive to chill hours include:

  • Apple trees
  • Stone fruit trees (peach, plum, apricot, cherry, nectarine)
  • Almond trees

A reputable nursery or supplier will be able to provide the chill hour requirements for each variety. When selecting fruit and nut tree varieties, select varieties that have a chill hour requirement at least 20% less than local averages. Planting a variety that requires less chill hours in an area with higher chill hours will result in trees flowering too early and being damaged by late frosts. Planting a variety that requires a higher number of chill hours in an area with low chill hours will result in little or no fruit production.

Some vegetables require lower Fall temperatures to convert starch to sugar.

To determine the chill hours for your location, first find your location on the Weather Underground "Wundermap" linked below. Click the bubble of the closest station to your home and write down the Station ID shown at the top (for example, KCALAKES1).

Go to Wundermap

In the Chill Hour Calculator linked below, enter the Station ID, start and end dates. The start and end dates will default to the dates typically used for chill hour calculations in your area.

Chill Hour Calculator

The calculator will show average the chill hours for the Station. Note that it sometimes takes a while for the calculations to complete. There is a progress bar beneath the "Calculate Chill" button.