Chill hours

Asked February 9, 2020, 8:46 PM EST

Are the number of chill hours changing in Willamette Valley due to climate change? Are we seeing any trends yet?

Clackamas County Oregon

1 Response

This is a great question regarding the potential impact of climate change on fruit growing in the region.

Since chill hours are defined as the number of hours between the temperatures of 32-45 degrees fahrenheit and winter hours above 60 degrees are subtracted from the totals, it seems logical that there would be reduced chill hours in the Willamette Valley in recent years and in the future.

I can't find any relevant research for the area, but here is an article on the subject focused on Yolo County California:

Because the chill hour requirements for most fruits and nuts are well below the typical chill hours in the region, it probably won't change the types of crops that will produce well here in the immediate future.

Raintree nursery has a good map and description of chill hours and ranges for various crops:

And if you want to do some more research, here is a chill hour calculator where you can select locations and date ranges: If you find a weather station near your location and perform a series of calculations for past years, you might be able to determine a trend.

And, if you want to hedge your bets, you could choose fruit and nut varieties with lower chill requirements.

I hope this information helps.