Have you ever had a fruit tree bloom but never produce any fruit? We often get this question and although there could be a couple of problems such as necessity for pollination or poor health, the main reason is due to what is called chilling hours.
Pretty weird, huh? Most clients are shocked and have no clue what chilling hours are, let alone how it relates to their fruit trees. Chilling hours are the amount of hours accumulated that are under 45 degrees during the winter or dormant season.
Think of it this way, chilling hours are the biological time clock for plants. Once the trees receive enough chilling hours, they determine it is time to leaf out and bloom to begin their production cycle. Blueberries, blackberries, peaches and apples all need chilling hours, and that is just a few on the list. For this article I will focus on fruit trees.
When we provide recommendations on fruit trees, we usually recommend varieties that require 750 or more chilling hours. For the Piedmont, we can expect to receive around 1,200 or more chilling hours during the winter, so any variety that can handle 750 or more chilling hours will usually produce a decent crop.
If we select fruit trees that have less than 750 chilling hours, we could run the risk of not having any fruit. Because our area requires fruit trees with higher chilling hours, we do not grow apricots, almonds, citrus and other types of peaches and apples. If you prefer to have a beautiful flowering tree in January or February, and no fruit, then selecting low-chilling varieties may be for you.
The biggest reason we need to know and understand chilling hours for fruit trees we buy is that some stores sell all types of fruit trees. The problem with selling all types of fruit trees is that one could buy a low chilling-hour variety and be disappointed that they never receive any fruit.
For more information on chilling hours contact local Extension agent Danelle Cutting at 704-216-8970 or visit these websites on chilling hours:
For blueberries: http://ncblueberryjournal.blogspot.com/2012/02/chill-hour-requirements.html
N.C. blueberry chilling hour model: http://www.nc-climate.ncsu.edu/cronos/blueberry/chill_model
Peaches: http://www.ces.ncsu.edu/hil/hil-327.html
http://www.clemson.edu/extension/peach/faq/what_are_chilling_hours_and_what_do_they_have_to_do_with_dormancy_do_cultivars_differ_in_their_chilling_hour_requirement.html
Apples and other fruit trees: http://www.ces.ncsu.edu/depts/hort/hil/ag28.html