Blueberry Chill Hours. What are they?

BlueberriesBlueberries are a perennial shrub that is relatively easy to grow.   Rabbiteye types are popular statewide and their fruit is delicious!  You may have read in agricultural science articles about “chill hours.”   What are they?  Why do they matter?  To answer those questions we are going to turn to science so, please pardon the charts!

According to UGA scientists Gerard Krewer and D. Scott NeSmith (Blueberry Cultivars of Georgia) blueberries require a certain number of chill hours each winter to produce the optimum fruit harvest.  Chill hours are the number of hours of winter temperatures 45 degrees F and below.  If blueberry plants do not receive the adequate amount of chilling, bloom and leaf development can be late and erratic.  This can result in a lackluster harvest.  To sum it up – blueberries have to have some cold winter weather.

Rabbiteye Cultivar Chilling Requirement
Premier550 hours
Climax400 to 450 hours
Brightwell350 to 400 hours
TifBlue600 to 700 hours
Powderblue550 to 650 hours
Vernon500 to 550 hours

How do we know how many chill hours we have had in our area?  The weather stations of georgiaweather.net have chilling hours calculators.  As of February 22nd:

Weather StationNumber of Chill Hours between Oct 1, 2015 and February 22, 2016
Blue Ridge1357
Atlanta941
Cordelle661
Valdosta369

So what does this all mean?  As noncommercial blueberry growers, it can give us some scientific information about our blueberry harvest and it gives us some insight into plant biology.  It also gives us another reason to watch the weather forecast and welcome cold winter weather.

If you don’t grow blueberries yet, give it a try!  See Home Garden Blueberries for more information.  Also contact your local UGA Extension office.  Many of them have plant sales this time of year and blueberries are often for sale.

Happy Gardening!

Becky Griffin

Becky Griffin

Community and School Garden Coordinator at UGA Extension
Becky Griffin helps school and community gardeners succeed! This includes organizing school garden teacher training for the summer months, managing the Center's garden presence on the web, and using social media to connect gardeners to the latest research-based gardening information.

Some of her recent and current work includes collaborating with partners on urban agriculture, working with school gardeners on STEM goals, and assisting communities in starting community gardens. In 2016 Becky launched the Pollinator Spaces Project which encourages community and school gardeners to add pollinator spaces.This project has been expanded in 2017 to the Georgia Pollinator Census project.Ask her about it!
Becky Griffin

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