Chilling hours for deciduous trees

Deciduous fruit trees are adversely affected by not receiving enough chill hours so they can properly break dormancy. This can be a problem in So. California and for some fruit trees it already is with poor flowering, off timing of flowering and new growth and a slow decline in trees affected by low chilling hours. Does low chill affect Liquidambar, Japanese Maples, Trident Maples, Hornbeam or Pomegranite?

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Am still looking for a good chill hour tree guide, but I found some chill hour-related resources.

Links to resources about your local weather and help determining local chill hours:

UC Davis Chill Hour Calculators:

Within Bonsai circles, you don’t hear people discussing Chill hours or Chill Units as frequently as they do within Fruit Growing societies because these hours/units relate to whether or not you can get a proper fruit crop or not. However, it is important to consider what grows well in your area, and part of that is certain trees need more of a dormant period before they exhaust all their resources and die.
But there are other factors mostly related to So Cal weather such has low humidity, temperature, etc. From my experience, i’ve seen Liquid Amber, Trident and Pomegranate do well in So Cal. However, Japanese maples while they will live in So Cal, they are much more challenging to grow in So Cal compared with say much of Nor Cal, Oregon, Japan, etc. If your looking for varieties that will do well in So Cal, I’d stick with what people from the local clubs are growing consistently-Juniper, Black Pine, Olive, Oak, tropicals etc…

Yes, people do not talk about chill hours since most people relate chill only to fruit and flower production. Chill also has to do with deciduous trees general growth. So my question is, if chill hours continue to decrease, will this cause some species of deciduous trees to slowly decline. We do well with Liquidambar, Tridents and Pomegranites, and yes, Japanese Maples do not like our dry climate down here. I have seen changes in trees from year to year and they seem correlated to chill in the fall/winter, but there are many other variables that it is hard to determine, hence the question. Could be nothing.

We are doing more with Ficus and Bougies, and of course the venerable JBP, Shimpaku and other Junipers.
Thx for your response.

I think a reduction or increase in chill hours could have an impact on the trees health and this could affect both Deciduous and some Evergreens esp for example high mountain pines. However, if the trees is placed in the exact same spot in your yard throughout the whole time, then I would look at other variables first. It could have a slight impact, but if a tree has done well for years in the same spot in your yard, then starts declining it’s probably not because of differences in chill hours from season to season. In a different scenario I have heard that Ponderosa pines will do well for a few years in So Cal, then slowly go down hill year after year unless grafted.