You've probably seen Applenuts posts on high chill apples in So Cal. Apples seem to be very forgiving with chill but cherries not so much. Supposedly some of the trees that beat expectations as you mention lose vigor over time because of the lack of chill. I guess you will find out if that is true or not.

There are fruits that have what might be called conditional chilling requirements. "High chill" apples might be the best example. They grow and fruit much better with high chilling, 1200+ hrs, but will still fruit with much less chilling. With low chilling growth is reduced and there tends to be lots of blind wood, ie bare wood that neither fruits nor sprouts vegetative shoots.

The fruit I've grown that is most affected by lack of chilling is northern highbush blueberries. They need 1200+ hrs or things go really badly, ie fruit can set with no leaves to mature any kind of flavor.

Most stone fruits are in between.

Climate zone 10 (probably on the border between 10a/10b), less than 150 hours of chill. Blenheim Apricot produced 11 fruits, though only about 5 of them fully developed. The tree had been planted in the ground only 2 years before that, so I'd say that's pretty good.

Rainier cherry in partial shade seems to have no problem blossoming, Bing cherry tree appears to be able to grow just fine, and there were maybe 10 blossoms on it last year. Still too young for fruit though, I'll have to let you know. Two months ago I grafted a small branch of Royal Minnie on it, so there is a possibility that might help induce the tree to be able to fruit, wake it up faster from its dormancy. The graft took and that branch is now bursting full of blossoms and leafing.

The lack of chill isn't a total curse here, it is possible to grow most types of tropical fruits (growing a banana and lychee tree, and there's someone not that far from here with a huge starfruit tree in their backyard). It's the type of place people are more likely to have an orange tree or avocado, but almost never an apple or plum tree. There are a few people around here who've planted a low-chill Babcock peach, but I've never seen much fruit in these trees.

A long time ago in the 40s, there used to be commercial orchards of Blenheim apricots around here. But I think the region gets a lot less winter chill than it used to due to all the development that has happened and asphalt paved surfaces.

The latest reports have shown that apples tend to be more adaptable to lower-chill areas than was previously thought. A field test by Tom Spellman of Dave Wilson Nursery showed that several apple varieties rated for 800 chill hours could grow just fine in Irvine (located in coastal Southern California, which only gets 50-100 real chill hours). The following apple varieties did surprisingly well: King Tompkins, Braeburn, Gravenstein, Cox's Orange Pippin. The trees tended to flower and set fruit throughout the year rather than a specific season.

https://www.youtube.com/watch?v=oiEEHRfAEWY


The results might have had something to do with the fact that the coastal influence has a moderating effect on temperature, and in the winter it rarely ever gets above 65 F in this region, higher temperatures being very detrimental to effective chill accumulation. In other words, the same moderating influence that prevents there from ever being any chill hours below 45 F may be, paradoxically, the same influence that allows the trees to grow well even in the absence of chill hours below 45 F.

Thanks Parker. I am curious where you are that had Blenheim in the 1940s. Blenheim apricot is the perfect tree for "experimenting" with chill because the tree is a) ubiquitous, at every nursery and big chain store, b) it usually will give a few fruit even in less than ideal locations and c) delicious.

I painted some small branches with dilute white latex paint this winter just to see what would happen and it seems to be delaying their blooming. I will see if they yield more or less fruit. The idea here is perhaps it delays heat absorption and prevents the early wakening that could sometimes be a problem in low chill areas. The tree definitely noticed the difference.- James