Interesting "chill hour" experiment in Irvine California

[greg_D]

A nursery owner has been running a trial with medium-to-high chill hour apples in Orange County. Almost all of them are doing very well, other than occasional issues due to heat waves and the need for a lot of mulch to protect the rootstock in the summer.

It seems like 'chill hours' for apples may accumulate above the commonly cited 45 F ceiling, or perhaps some varieties can adapt to having flowering triggered by heat (maybe both?).

https://www.youtube.com/watch?v=htz5BUNMB38

[Draak]

I finally looked up chilling hours, and I was surprised! There is a range of acceptable chilling hours. Also, if you don't have enough chilling hours, you can get a little chemical help to get some fruit set. From wikipedia:

A four-year study of Ruston Red Alabama peach, which has a threshold of 850 chilling units, demonstrated that a seasonal chilling deficiency of less than 50 units has no effect on harvest. Deficiency of 50 to 100 units may result in loss of up to 50% of expected harvest. Deficiency of 250 hours and more is a sure loss of practically whole harvest; the few fruit will be of very poor quality and have no market value.[7] Rest-breaking agents (e.g. hydrogen cyanamide, trade name BudPro or Dormex), applied in spring, can partially mitigate the effects of insufficient chilling. BudPro can substitute for up to 300 hours of chilling, but an excessive spraying and timing error can easily damage the buds.[7] Other products such as Dormex use stabilizing compounds.

[greg_D]

Thank you that makes a lot of sense. Also I just realized there's a temperate forum. Sorry for posting this in the wrong place. Would delete it but that doesn't seem to be an option.

[Galatians522]

I am sure one of the moderators can move this discussion. Dormex is highly toxic, by the way. I have read that many low chill cultivars will still produce acceptable yields with only half of their chill requirement--this does seem to hold true from what I have observed personally.

[Tlaloc]

I wouldn't rule out dropping a big bag of ice on the base of the tree during cold nights. Especially if it's only 1-3 trees.

[Eggo]

Also wanted to add some additional info for everyone.  Gary Matsuoka of Laguna Hills Nursery has had quite a bit of experience with apples in a southern california climate.  Due to the lack of chill, most apples will slowly bloom for months branch by branch.  There's quite a bit of good info in the vid. 

https://youtu.be/XLT00vBPNQY

[Galatians522]

I don't think that ice would do much. However, people who live in dry climates could potentially take advantage of evaporative cooling to create chill with a misting system. If you study wet and dry bulb charts, you can see that when the relative humidity is low there are some significant differences between the two. When the relative humidity approaches 100% there is no difference between the two (because there is no evaporation).

For example, the current temperature in Los Angeles is 62 with a dew point of 33 (40% relative humidity). If I understand the math correctly, an ideally implemented misting system under those conditions could potentially lower the temperature almost 10 degrees! That would put things in the range that could potentially create chill hours for some things (assuming the tree was in a dormant state).

By comparison, Tampa is currently 72 with a dew point of 71 (94% relative humidity). An ideally designed misting system under these conditions could potentially lower the temperature by approximately 1/3 of a degree. Which of course would be a total waste of time.

[greg_D]

Also wanted to add some additional info for everyone.  Gary Matsuoka of Laguna Hills Nursery has had quite a bit of experience with apples in a southern california climate.  Due to the lack of chill, most apples will slowly bloom for months branch by branch.  There's quite a bit of good info in the vid. 

https://youtu.be/XLT00vBPNQY

Fantastic video thank you

[Eggo]

Also wanted to add some additional info for everyone.  Gary Matsuoka of Laguna Hills Nursery has had quite a bit of experience with apples in a southern california climate.  Due to the lack of chill, most apples will slowly bloom for months branch by branch.  There's quite a bit of good info in the vid. 

https://youtu.be/XLT00vBPNQY

Fantastic video thank you

Greg, I'd also recommend his soil class videos. Gary's a legend. If you are not aware of him, his approach to soil will definitely change the way you garden. Real soil vs compost/bark medium makes a huge difference.  Most nursery pretty much sells you a plant in a medium that will kill the plants in 6 months.  Don't mean to side track from the original post too much.