IMPORTANCE OF CHILL REQUIREMENTS
Fruit trees require a period of Dormancy (rest) each year. They stop producing buds and fruit, and essentially take a nap to rebuild their energy to produce another crop. This is accomplished by wintertime chill, and is referred to as “Chill Hours.” Do not underestimate its importance.
The Dormancy period also makes the buds wait till winter is completely over before they open so they don’t freeze. Adequate Chill Hours leads to more blossoms and a heavier fruit crop. The number of necessary Chill Hours is different for each tree and plant.
HIGH CHILL VS. LOW CHILL
- High Chill fruits require a long period of wintertime cold or fruit production will suffer greatly, and might result in a complete crop failure.
- Low Chill fruit varieties are especially bred to flourish in the heat of the South. They require very few Chill Hours.
THE IMPORTANCE OF GRAFTING ROOTSTOCK
Not all varieties of apple trees have the same number of Chill Hour requirements. Also, the same variety of apple tree might vary in their chilling requirements. This depends on the type of rootstock they are grafted on.
In other words, some trees (or plants) will be more “fussy” depending on which garden nursery you purchase them from. Not all nurseries use the same hardy rootstock.
RELATED ARTICLE: CHILL HOURS IN PLAIN ENGLISH
This explains why in some garden catalogs a fruit tree or plant might be listed as surviving as far north as Zone 4, while another catalog might say Zone 5.
This is a clue not only to how much cold they can take in the winter, but is also a clue to the number of Chill Hours they need. (I wish someone had told me this years ago. I had to find this out the hard way.) Failing to provide the correct number of Chill Hours will drastically cut down on the size of next season’s crop, produce poor fruit quality, or even cause a complete crop failure.
RELATED ARTICLE: CHOOSING THE PERFECT FRUIT TREE
NOTE: There is strong disagreement among gardening experts on the correct way to calculate Chill Hours. Trying to read through the information on the subject is just all sorts of good clean fun. It tends to raise more questions than it answers. I defer to the knowledge of experienced elderly gardeners who have lived through enough brutally cold winters to know that nature tends to have a mind of its own.
HAPPY PLANTING! Susan
For more in-depth information on GROWING YOUR OWN FRUIT