What are chill hours and why do I need them?
I hear this question a lot.
I'm Christy Wilhelmi from Gardenerd.
Today I'm going to answer that question.
If you are planning to grow fruit trees or berries in the coming season chill hours are
going to be something you need to know about.
So, let's start with what are they.
Technically, chill hours are the number of hours where temperatures are between 32 degrees
F and 45 degrees F, over winter, during a tree's dormancy period.
Now some people also subtract the number of hours where temperatures during the winter
exceed 60 degrees F. That actually reduces your total number of chill hours throughout
winter.
So if you live in a place where you suddenly get a heatwave in December like we do here,
you might actually have fewer chill hours than you think you do.
Chill hours are important for fruit trees because they need this dormancy period and
this chill requirement in order to break bud and form fruit the following season.
And if they don't get that, you may get lots of leaves but no fruit.
So let's talk about the different types of fruits that need different requirements for
chill.
So a lot of fruit trees require anywhere between 600 and 1,000 chill hours over that winter
period.
And if you live in a coastal or a warm-winter climate you aren't going to get those numbers.
But if you live in a northern or a cool-winter climate you will have no trouble getting those
kinds of numbers.
So for those who want to grow apples, pears, cherries, and some of the stonefruits, you're
good if you get snow on the ground or really cold temperatures over winter.
In warm-winter climates like we have here in Los Angeles, we have to choose low-chill
varieties of apples, pears, stonefruits, cherries, and even berries, but we'll get to that in
a second.
The good news for warm-winter climates and places with really mild-winter temperatures
is that you can grow the sub-tropicals and tropical fruits because they have very low
chill.
Fig trees, pomegranates, loquats like here, guavas, olives, those are all going to have
low chill hours.
And low chill means something around, you know, usually below 500 but really below 300
chill hours.
Three to four hundred chill hours.
We here have a Fuji apple tree that requires 500 chill hours but we've got it tucked in
a spot that gets morning shade and so it actually fruits and flowers.
Even though we only get maybe 150 to 300 chill hours a year.
So you can play with this.
When it comes to berries, you may or may not have trouble growing blackberries, raspberries,
boysenberries, logonberries.
They tend to be pretty well adapted to different climates, but there are high-chill and low-chill
varieties available.
Blueberries, though, are a big deal.
You need to choose low-chill varieties if you live in a warm-winter climate because
the typical varieties usually range between 400-800 chill hours.
But the low-chill varieties will fruit at as low as 150 chill hours.
So that's good.
There are some fruits like citrus or strawberries that don't have a chilling requirement because
they are meant to be grown in warm places.
So you may need to, if you choose to grow a citrus tree in a cold-winter place, you
probably, you'll need to bring that in or protect it over winter in a green house or
a sunny enclosed porch.
Strawberries you can usually mulch those with straw and they'll be fine throughout the season
and will come back the next year.
Or replant, as many people do.
Once you figure out what kind of fruit that you want to grow, do your research and find
the variety that's going to grow with your chilling requirements.
If you need help figuring out how many chill hours you get, there are a lot of websites
where you can look it up.
A lot of university Agricultural websites will have that information.
So do a search, check it out.
You can look for "chill hours" + Your zip code and you'll probably find a few results
there.
If not check your local nursery or your local University Agricultural department.
Once you know how many chill hours you get you can choose which varieties will grow in
your space.
And then you'll actually get fruit, which is the whole point, isn't it?
So make the right choices.
Find out how many chill hours you need where you live, pick the right fruits based on that,
and you will have success.
For more information on chill hours, growing fruit, and a whole bunch of other stuff, check
out my new book, Grow Your Own Mini Fruit Garden.
And of course, for growing all kinds of other stuff, including vegetables in small spaces,
you can check out Gardening for Geeks.
Besides that, we've got tons of free gardening information at Gardenerd.com.
Consider becoming a Patreon subscriber to support the free stuff we do at Gardenerd
and of course, happy gardening!