Pear trees evolved in regions with cold winters and that means they need a bit of cold weather to survive and reproduce.
I know, I’m asking myself the same thing you are: “why the heck would anyone or anything actually prefer to be cold?!” Or am I the only one wrapped in blankets even during the summer?
Pears can’t reproduce unless they spend a certain amount of time below a certain temperature. This is known as “chill hours,” and several fruit trees have this requirement.
So if you want to enjoy an abundant harvest, you’ll need to understand the specifics about temperature and timing of the cultivar you choose to grow.
If you need a refresher, you’ll find our guide to growing pears here.
In this guide, we’ll cover all the details about pear chill hours and you’ll be ready to grow productive trees that will produce all the fruit you can handle.
Here’s what we’ll go over:
Let’s start by defining our terms.
What Are Chill Hours?
Many fruit and nut trees, including pears, need a certain amount of time within a specific temperature range to break dormancy.
You might hear that pears need 1,000 chill hours. That just means that a tree needs to experience 1,000 hours below 45°F.
It doesn’t have to all be in hourly increments, though. The exposure could be 60,000 non-consecutive minutes at any time during the fall and winter.
So a few minutes one day and a few more the next could add up to all the time required.
Let’s also be clear that a chill hour is 60 minutes within the appropriate temperature.
You might also hear the term “chill requirement,” which is the period needed within a certain temperature. We count this period most commonly in hours.
Think of chilling requirements as the accumulation of the measurement unit of “chill hours.”
Don’t confuse chill hours with the post-harvest practice of chilling fruit. Growers will store the fruit in a cool area to allow them to fully ripen before putting them on the market.
This is also called “conditioning” and it is completely separate from the low temperatures that a growing tree must experience.
Why Fruit Trees Need Chilling
Why on earth would a tree evolve to have this kind of behavior? It actually goes hand-in-hand with the same reason some seeds need stratification, or a period of time in cold temperatures.
If a tree were to break dormancy in the middle of winter and start flowering, the flowers would almost certainly be killed by a freeze.
No flowers means no fruit, and no fruit means the tree won’t be able to spread its genes around. So it needs to avoid breaking dormancy too early at all costs.
But a tree doesn’t have a calendar with the last predicted frost date circled in highlighter yellow like I do.
They have to rely on other mechanisms to indicate when it’s safe to flower.
So to let the tree know when enough of winter has passed that it’s okay to start emerging from dormancy, the tree needs to experience enough time under a certain temperature.
When, for instance, 600 chill hours have passed, the plant knows that it’s likely to be close to spring.
Temperatures colder than 45°F won’t delay flowering, but if it’s warmer than the particular species requires, the tree won’t emerge from dormancy.
Or it might partially emerge when the days grow longer and warmer.
Those are the other factors that signal to a tree that it’s time to emerge from dormancy: more daylight time and higher temperatures.
In a perfect world, the tree will experience the right number of chill hours, the days will get longer, and the temperatures rise.
At that point, the plant says “the coast is clear” and starts to flower. But if the chilling condition isn’t met, the tree might decide it’s not safe after all.
That’s why if a tree receives almost but not quite enough chill hours it might produce a less abundant harvest than usual or the fruits might be smaller in size than usual.
Chill requirements are a pretty smart adaptation, if you ask me!
How Many Hours Do Pears Need?
The amount of time a pear tree needs below 45°F depends on the cultivar, so we can’t say that all pears need a specific number of hours.
In general, their chill needs range between 200 and 1,000 hours. That means you’ll need to learn the specific needs of the particular pear you’re growing.
To add to the fun, most cultivars have an acceptable range of time, so growers will have varying recommendations.
For example, ‘Bartlett’ has growers recommending anywhere from 400 to 1500 chill hours.
Research by professor Kitren Glozer at U.C. Davis and Chick Ingels, Extension Farm Advisor at the University of California, found that ‘Bartlett’ performed best, at least in California, when they had about 820.
So don’t worry too much if you are looking at a cultivar that specifies a certain amount of time and you don’t have that exactly.
You can assume that anything close to the stated hours should be fine.
Every tree is a little different, but here are some of the requirements for common pears:
‘Anjou,’ ‘Bartlett,’ ‘Blake’s Pride,’ ‘Harrow Delight,’ and ‘Summercrisp’ require about 800 hours.
‘Sunrise’ and ‘Warren’ aren’t too far behind at 600.
‘California’ and ‘Seckel’ are practically the same, requiring about 550.
The favorite ‘Bosc’ needs about 500, followed by ‘Flordahome,’ ‘Kieffer,’ ‘Magness,’ ‘Moonglow,’ and ‘Orient’ at about 400.
‘Comice’ wants anywhere between 200 and 600, while ‘Perdue’ is much less demanding at 200.
‘Baldwin,’ ‘Hood,’ and ‘Pineapple,’ are on the low end of the scale, requiring just 150.
Chill Out!
It might seem like a nuisance, but chill requirements are an important evolution that ensures the pears will be able to flower and produce fruit successfully.
If you’re picking a tree for your garden, you have to take the chill requirements into account.
What types of pears are you growing? How many appropriate hours do you have in your region? Let us know what you’re working with in the comments section below!
And for more information about growing pears in your landscape, check out these guides next: