What You Need To Know About Chill Hours

Chill Hours

Have you ever looked to purchase a fruit tree?  Let us take a peach for example, google peach tree; you get hundreds of sites selling thousands of varieties.  First, you need to know your gardening zone, and what’s this thing about chill hours?

What Are Chill Hours

To successfully grow fruit trees, it is vital to understand chill hours. If you mistake and select a fruit tree variety without understanding chill hours, you will waste your time with poor harvests.

Chill hours are defined as any temperature below 45F.  Depending on who you talk to, some will tell you the temperatures have to be between 45-34F.  Sometimes people make things more complicated than they need to be. 

Why Are Chill Hours Critical

For some plants to produce flowers and fruit, they need a dormant period.  This dormant period is achieved whenever the plant is subjected to colder temperatures known as chill hours.  Fruit trees, berries, and nut trees all need these dormant periods to help regulate the growth.  Without sufficient dormant periods, some plants are not able to flower or fruit.

When you begin to look at the fruit trees, you see there are different varieties of high chill and low chill. Low chill needs less than 300 and high chill requires more than 500 chill hours.  Now there are low chill requirements for a lot of the most common fruits. Careful, though, do not be tempted to plant a low chill variety in an area that gets high chill hours. Although it seems like a gardening hack, you run the risk of the plant breaking dormancy too early.  There is always a catch. If your plant breaks dormancy too soon, the flowers or blooms will fall off.  No flowers mean no fruit.

Do not confuse chill hours with cold hardiness.

What’s excellent about chill hours is that they don’t have to be consecutive. Chill hours are cumulative from late October until February or march, depending on your area. Hours that are below freezing do not count. 

Chill hours may be more important than location when selecting a fruit tree for your garden. If you don’t, you can waste time and money.  You will be disappointed if you live in an area that only receives 400 chill hours but buy a tree that needs 800 chill hours. 

What Types of Trees Require Chill Hours

There are not many fruit trees that do not require some amount of chill hours to produce fruit.  Out of all the fruit trees, Apples have the highest chilling, followed by apricots and peaches. Figs, olives, and quince have the lowest chill requirements, followed by persimmons, pomegranates, almonds, and chestnuts.

Most fruit trees are deciduous, meaning they lose their leaves over winter.  Planting a variety that doesn’t receive enough chill hours and the leaves often will not drop from the tree.  The tree will not enter a state of dormancy and, therefore, will not produce. 

The number of chill hours will vary depending on the cultivar of the fruit tree.  Most apples require well over 500 chill hours. But check out how the chill hours vary depending on the cultivar.

Gala – 500 Hours

Golden Delicious- 600-700 hours

Red Delicious- 800 hours

Anna- 200 Hours

Golden Dorsett- 200 Hours

Anna and Golden Dorsett are excellent choices for people in Houston and other areas with mild climates.

Fruit trees are not the only plants that require chill hours of some sort.  Do you remember the cold stratification example with the milkweed?  Garlic, blueberries, tulips, nut trees, and others need cold temperatures to grow well or grow at all. 

How To Find How Many Chill Hours For My Area

One of the easiest ways is to google it. You can also ask your local agricultural extension office.

Chill hour lookup tools

Your local agriculture extension agency will have resources, where you can find out the average amount of chill hours your area receives. Remember, though, this is linked to the weather so it is hard to be exact but the average will get you started off correctly.  Equipped with this knowledge as well as your gardening zone, you are now ready to venture out to a nursery or website and order a fruit or nut tree or bush.

Remember the motto –

JUST GROW IT!

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