The chill hours are probably nothing new to you if you grow apples. What are apple chill hours, for those of us who are unfamiliar with apple cultivation? How many hours of chilling are necessary for apples? Why is chilling necessary for apple trees? Everything seems a little unclear, but all the information you need about apple chilling is in the next article.
Information on Apple Chilling
As you browse a catalog of bare root apple trees in your particular USDA zone, you see that in addition to the hardiness zone, there is another number displayed. This is how many apple chill hours the tree needs in the case of apples. All right, so tell me about apple tree chill hours.
The number of hours that temperatures stay between 32 and 45 degrees Fahrenheit (0 and 7 degrees Celsius) is referred to as chill hours, or chill units (CU). These chilly hours are exacerbated by longer nights and colder temperatures in the fall and early winter. Due to the breakdown of the hormone that causes dormancy, this is a crucial time for apple trees. As the weather warms, this enables buds to develop into flowers.
Why Is It Necessary to Cool Apple Trees?
An apple tree’s flower buds may not open at all or may open later in the spring if it does not receive enough chill hours. Delays in leaf production are another possibility. Additionally, blossoms may bloom at irregular intervals, which may seem advantageous, but the longer the bloom period, the more susceptible the tree is to disease. Fruit production will also be impacted by a lack of chill hours, as one might anticipate. Therefore, it’s important to match your apple variety to your USDA zone and the chilling hours that the tree needs. A low-chill tree purchased in a high-chill region will break dormancy too soon, resulting in damage or even death from the extreme cold.
How Many Cool Hours Are Necessary for Apples?
The cultivar has a major influence on this. There are currently over 8,000 different types of apples in the world, and more are added every year. While some low chill apple varieties only need 300 chill hours, the majority require 500 to 1,000 chill hours, or temperatures below 45 degrees Fahrenheit (7 degrees Celsius). Compared to other types, low chill varieties can withstand hotter summers and require fewer than 700 chill hours.
What Apple Trees Have The Lowest Chill Hours?
High chill apples require more than 1,000 chill hours, while medium chill apples need 700 to 1,000. High chill apples do not grow well in low chill climates, but low chill and medium chill apples can be grown in high chill areas. There are still many medium- to low-chill cultivars of apples, even though the majority require high chill hours.
- The minimum chill time needed for Fuji, Gala, Imperial Gala, Crispin, and Royal Gala is 600 hours.
- 500–600 chill hours are required for pink lady apples.
- It takes 450 to 500 chilling hours to make Mollie’s Delicious.
- Ein Shemer, a yellow/green cultivar, and Anna, a golden, delicious apple, can withstand 300 to 400 chill hours.
- Less than 100 hours are needed for the Bahamas’ Dorsett Golden, a truly low chill apple.
