If you have any personal experiences related to certain species or cultivars that you would like to share (along with your location), such as average first or full bloom dates (roughly 1-5% or 90-100% open), ripening dates, disease resistance, etc... (the more detailed, the better, but basic information can be very useful too), or if you spot a potential inaccuracy on my website, let me know, and I'll take it into consideration.
You can reach me at
(enable javascript)

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 is accurate enough to give you an idea of what to expect, but an improved version based on the Dynamic Model could end up making an appearance at some point.  

Cultivars 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 cultivars 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 exposes the blossoms to a greater chance of experiencing frost damage.


Additional Comments

Bloom labels for species and cultivars are used in different ways.   Species are compared to all other species, while cultivars are compared to cultivars of the same (or very similar) species.   For example, Apricots are known for blooming very early in the season, making it difficult for them to produce in certain regions, so Prunus armeniaca, and other apricot species, are labeled as "very early" bloomers.   A "mid-late" blooming apricot still blooms quite early in the season, it just blooms a few days to a week later than most other apricot cultivars.   Some fruit, such as honeyberries, also bloom very early.   However, their flowers can handle significantly lower temperatures than most other fruits, so honeyberry species are labeled "very early (hardy)".   Apples bloom fairly late in the season.   Early blooming apples, like Zestar, will still bloom almost 2 weeks later than the average apricot (depending on the climate).

Months or days are used for the species Ripening label (but not for specific cultivars).   This is not based on the time it takes from bloom to fully ripened fruit like it is on other websites.   It is based moreso on the time it takes for fruit to ripen from the average starting date of the grow season (in either hot or cool summer climates).   I believe this will be more useful to the average home-grower, particularly those with a shorter grow season, since some fruits bloom very early, while others bloom very late.   I may replace this with "heat units" at some point in the distant future if I ever obtain enough data to confidently do so.

You are better off assuming "self-fertile" plants are "partially self-fertile" because having a pollinator usually increases yield.   Sometimes you may prefer to not have a pollinator though.   For example, some species, such as Asian Persimmons, produce seedless fruit this way (parthenocarpy).

If you see something like (hardiness) "Zone: 5 (4)" on the site, it means it's probably hardy down to zone 5, but if it's not, it's more likely to be hardy down to zone 4 rather than a zone higher than 5.   Alternatively, "Zone 4 (5)" means there may be a little more evidence that it's hardy down to zone 4, but if you want to play it safe, you're better off getting it only if you're located in zone 5 or higher.   I also want it to be more visible to people who search for cultivars based on "Zone 4" because it's a good cultivar to experiment with, for those who are up to it.

I am also increasingly using a formats such as 5a/6/4a, 5a/6, and 5a/4b when referring to species.   5a/6/4b means that the majority of named cultivars from this species appear to be hardy down to zone 5a, but some are as high as zone 6 and others are as low as zone 4b.   Sometimes the hardiness of a species doesn't have as much variation, so I'll only use something like 5a/6 or 5a/4b, with the first one (5a, in this case) always meaning that it's the most common among (the most widely sold or newly developed) named cultivars.

While taste is subjective, some things, such as certain cultivars, appear to be more or less liked than the others.   This is probably because we are drawn towards certain levels of sweetness or flavors, among many other things, on a genetic level, and as a result, some things are less subjective than others.   When I notice that the flavor of a certain cultivar has a better reputation than most others, that is, when it's coming from people who have experienced many cultivars, I may mention it.