Find Your Thrill with Blueberry Chill (Hours)
What's a Chill Hour?
You're happily choosing your blueberries from our catalog or website when you suddenly notice extra numbers in the descriptions. Number of chill hours? Isn't it enough to know your USDA plant hardiness zone? That's about cold temperatures -- why do you need another number?
The USDA zone tells you the coldest temperatures in your area. Broadly speaking, the chill hours tell you how long the cold temperatures last. The traditional definition of a chill hour is any hour under 45°F. But wait, there's more. Academics have competing theories on what "chill" means. Some say the chill only counts if the temperature is between 45°F and 34°F. Others differ over chill calculations for the Utah model, and let's not forget the new Dynamic model.
How to Count Chill Hours
Here's the best way to count chill hours: get someone else to do it! Luckily, there are institutions already tracking this information. Farmers and gardeners in most California counties have access to official data on chill hours through the Pomology Weather Service at the Fruit & Nut Research Information Center. This service records chill hours -- so you don't have to. If you're not covered by this weather service, contact your Master Gardeners or local Farm Advisors to find out your local source of chill hour information.
Chill Hours are Important to Blueberries
Blueberry bushes cannot move to better climates -- they have to adapt to their environment. Blueberries need a specific number of cold hours each winter to regulate their growth. Without sufficient cold, flower buds might not open in spring, or they might open unevenly.
On the other hand, planting a low-chill blueberry in a high-chill area could cause the plant to break dormancy too early, exposing it to frost damage. It’s important to match your blueberry variety to your local chill hours to ensure a thriving plant and bountiful harvest.
More Blueberry Information
Will you be planting your blueberry bushes in rows for a you-pick farm? You'll appreciate Grow the Best Blueberries, an info-packed booklet from the Storey Wisdom series.
Hoping to plant blueberries as a hedge or mix them into your edible landscape? Find creative ways to use blueberries in The Fruit Gardener's Bible.
Be sure to match your new blueberries to your local chill hours -- use the left menu on our blueberry bush page (clicking on Filters) and then click on Chill Hours. Look forward to blueberries that live happily ever after.
1 comment
Blueberry chill hour article was very helpful. I’m considering moving to 40 acres in NC. Interested in highbush blues, mulberries or gojis. Most especially any NC agricultural info, incentive or subsidy. Thank you for any information.