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Climate

Most of the information here is based on the northeastern quarter of the United States at a normal elevation. The same results may not be experienced in other regions.   This includes their flowering and ripening behavior, which I am primarily speaking of at this time.   I have noticed that some species (e.g. apricots) behave much differently in the hot mediterranean climate of California's Central Valley, but others, such as peaches, may be more aligned.   Pawpaws, and possibly other species, supposedly behave differently in the higher elevations of the Appalachian mountians than they do at a more typical elevation nearby.   Conversely, it currently appears that species grown in (at least some of the more populated areas of) the Pacific Northwest tend to follow a similar order as to what I have listed, but the fruit may require more days to ripen than they do in most of the northeastern quarter.   However, I still need to take a deeper look into all of this someday.  


Chill Hours

Some plant species, particularly ones native to the temperate latitudes, require a certain amount of chill hours to prepare for the next grow season.   Chilling can be received between the temperatures of 32F to 55F, but it is most efficient somewhere between 35F to 50F.   Additionally, temperatures above 60F can reduce accumulated chill hours, to some extent.   The most common chill hour map, however, is strictly based on temperatures between 32F and 45F.   With the exception of Mediterranean climates, since they typically receive significantly more chilling hours than what is displayed, it should be accurate enough to give you an idea of what to expect until an improved model becomes accessible to the public.

Varieties that are said to require 800 chill hours don't exactly need 800 or more to fruit.   One study found that you can still grow a decent crop after receiving about 50 to 100 chill hours less than the recommended amount.   Below that will not only reduce crop set, it will also reduce fruit quality as well as delay bloom, reduce pollen production, and discourage a healthy leaf set.   Receiving 300+ chill hours less than the recommended amount may completely prevent the tree from setting fruit and even cause some dieback.  

Planting varieties that require a much lower number of chilling hours than your area generally receives may not be a good decision for some.   Climates with large, frequent temperature swings during the winter or early spring often prevent them from fruiting (this is a problem throughout most of the US).   Not only are their chilling requirements satisfied early in the year, but the amount of heat units (grow degree units) required to bloom are easily accumulated as well.   This dramatically increases the possibility of an early bloom, which further threatens the blossoms with frost damage.


Images with a URL ending in 'ARS' originated from the Agriculture Resource Service.
Images with a URL ending in 'NFC' originated from the National Fruit Collection.