What Are Chill Hours?
What are Chill Hours?
Fruit trees need a period of dormancy with a certain number of Chill Hours to regulate their growth, produce flowers and to fruit. Contrary to popular belief, this is not an accumulation of time spent on the couch with a glass of wine binging a new show. A chill hour is defined as any hour when the temperature is between 45 and 32 degrees. The chilling requirement is the cumulative number of chill hours required between November and March for a particular cultivar to break dormancy. Chill hours are different from cold hardiness, which is the lowest temperature that a tree or plant can tolerate without dying.
If a tree doesn’t experience adequate chill hours during the winter, the production of leaves may be impacted, the flower buds may not open or open unevenly, which will reduce the crop size. Regions vary greatly in the chill hours they receive, and various cultivars of the same fruit may require different levels as well; e.g., the apple ‘Red Delicious’ requires 700 chill hours while ‘Anna’ requires just 200.
Keep in mind chill hours are commercially defined for orchard management and crop production and are not as important to a home grower for a successful harvest. Currently there is scientific research and debate underway regarding the actual impact of variations in the number of chill hours and crop size as it relates to home fruit growers. This research indicates that if the discrepancy between the actual chill hours your tree receives and its classified requirements is less than 35%, your harvest may have some impact, but it is unlikely to make a significant difference. Cherry trees are believed to be the most impacted by chill hours.
East Bay Nursery carries a wide variety of fruit trees with low and moderate chill hour requirements, all of which have been proven performers here in the Bay Area.
View our entire selection of fruit trees here: Fruit Tree List
Our selections with the lowest requirements include
Apples – Anna, Dorsett
Apricots – Gold Kist, Katy
Aprium – April Delight
Asian Pear - Shinseiki
Cherry – Royal Lee, Minnie Lee and Royal Crimson
Plums – Burgundy, Satsuma
Pluot – Dapple Supreme
Peach – Saturn, Babcock, Sauzee Swirl, Mid-Pride
Nectaplum – Spice Zee
Nectarine – Double Delight
Pears – Kiefer – 350
Figs, Pomegranates, Quince, Persimmons – all require 300 or less chill hours
View our entire selection of fruit trees here: EBN’s Fruit Tree List
