chill hours (forum)

John O starts with ...
How do I confirm chill hours for Mt Sturt, Qld?
Silly question: does the number of chill hours need to be continous? or does overnight count?

Time: 23rd October 2010 10:44am

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kert says...
I suggest you look up Dave Wilson website and then go to technical notes then to chill hrs. It is as good as I 've seen

Time: 24th October 2010 5:17pm

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Tommoz says...
I will probably stop recording chill hours for this winter as there are no longer any temps below 7 degrees.
If anyone has done the number crunching before I'd appreciate some advice on how to use formulae in Microsoft Excel.

My temp recorder was set to record the temp every 20 minutes, which will make the matrix much longer but more accurate.

Technically I could use the Utah model or another one, whatever's easier. If you know what to do please post.

Time: 27th August 2013 11:34pm

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Original Post was last edited: 28th August 2013 2:27am

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Mike says...
I have seen a few peach trees in Cairns lately which are festooned with blossoms and ladened with fruit.There has not been one chill hour in the last 25 years yet the peaches still bloom and fruit.Even Florda Prince is reputed to need over 100 chill hours.I would not have much confidence in the accuracy of chill hours given for various species and varieties judging by the experience of growers.

Time: 28th August 2013 7:41am

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yry says...
Peach tree in Cairns laden with fruit? Are you sure? That's worth a photo!

Time: 28th August 2013 9:43am

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Mike says...
I saw one at Mt Sheridan on Saturday that was a real crackerjack in someones' yard.Peaches are pretty easy to identify.The second may well have been a tropic snow and not a florda prince.Next time I'm in that neck of the woods I'll hang over the fence take a snap.

Time: 28th August 2013 10:19am

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Brain says...
happy to help with excel questions :)

Time: 28th August 2013 11:09am

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VF says...
I've found the chill hour, 7 degree and under formula to be unreliable. It doesn't take heat units into consideration, and I'm guessing other things that alter flowering and fruit set too. I've only had 7 nights this winter where it got to 7degrees or under - I still have med.chill blueberries flowering profusely and setting fruit at the same time as my mangoes,sapodilla and rollina flowering. Go figure?

Time: 28th August 2013 3:18pm

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BJ says...
Yeah, I have plums setting now and we have had hardly any chill. Blueberries and peaches are going bonkers. Most plants broke dormancy half way through winter as well, so I could only count the first half of winter in my chill equations, which was warm and wet.

Time: 28th August 2013 3:52pm

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Tommoz says...
What? Nothing counts after break of dormancy? Damn, that's when I started to get some proper chill.

Using the simplest model of one chill unit for every hour between zero and seven gave me 460. But I would need to adjust for the warm temperatures.


Time: 28th August 2013 4:43pm

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Original Post was last edited: 30th August 2013 6:53pm

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Brain says...
The Chill hours are really an indicator of the plant's original geographical dispersion/location and where it was last grown successfully and fruiting consistently.

I think many of us are trying new things and are now discovering that these stone fruits can be quite adaptable and surprising.

I see that my Stella cherry is starting breaking buds now and this Brisbane winter has been very warm. It had green leaves 2 weeks ago and these ones were formed at the start of the winter. (go figure) I've got to wait and see if flowers would break out.



Time: 28th August 2013 4:59pm

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yry says...
If you define chill hours as below 11 deg C. tehn Mt Sheridan DOES get chill. Mystery of peaches solved.

Time: 29th August 2013 9:11am

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Mike says...
Changing the definition doesn't always change the physiological requirements of the plants.These are supposed to have been determined but perhaps there are more variables at play.The 3 or 4 hours below 11c at Mt Sheridan obviously satisfies the triggers in this particular plant.

Time: 29th August 2013 9:16am

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BJ says...
11c? So I've heard 10c, 7c, and now 11c. I am less inclined to listen to folks about calculations and definitions of chill hours and just plant a bunch of things and try them out. It seems we can get plants in the 400 chill hours (under 7c as advised by the growers) region to fruit here, even with ~100 chill hours. I'm tempted to grow Apricots next.

Time: 29th August 2013 9:23am

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VF says...
Trial and error is the go at my place. Have started with 'safe' plants, ie low chill sub-tropicals, and have been pushing the limits on both sides of the temperature ranges a little at a time. Some pleasant surprises have followed.

BJ, I saw a Moorepark a couple of weeks ago at Bunnies and was tempted myself! If Peaches set in Cairns.....

Good luck with the Cherries, Brain.

Time: 29th August 2013 10:35pm

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BJ says...
Just to add to the chill conversation, my plum with 350hrs requirement is setting better than my plum with 275hrs requirement... We havent had near 35hrs this year.

Time: 30th August 2013 10:43am

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Brain says...
I did research on the chill periods required for cherry, and this is the excerpt from this study.

"Hence, successful production of cherry under warm climatic conditions (with the absence of adequate winter chilling) is not possible."

http://popups.ulg.ac.be/Base/document.php?id=703

(it's applicable to other stone fruits as well, so worht a read).

Anway, I still went ahead and brought my trees! LOL.

Time: 30th August 2013 1:10pm

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Tommoz says...
@Brain Good luck with the Stella but I think it will really struggle in Brisbane. Minnie Royal-Royal Lee from Flemings is super low-chill but I haven't heard back from those who bought it and unfortunately there was a problem this year in production so 2014 will be next chance to buy it. The next best cherry for low chill is Lapins (4-500).

@BJ I would recommend Kingston Royal apricot as it is apparently from Kangaroo Island (and tastes fantastic). The other two low-chill apricots are Katy and Blenheim (Royal).

@VF Don't make the mistake of getting a Moorpark if you don't get the 600 chill hours. Sure it's a famous name but the other types I mentioned above are very good.

@George Unfortunately Flavortop nectarine requires about 650 chill hours which no part of Sydney got this winter.

Time: 30th August 2013 11:26pm

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Original Post was last edited: 31st August 2013 1:22pm

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Chris says...
That's the problem with Sydney, George. It is becoming more a marginal climate for some stone fruit.
It was the warmest winter on record, so expect the classic symptoms of lack of chill: delayed leaf and leaves on the tips but nothing for 30cm below.

Time: 31st August 2013 12:12pm

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yry says...
Add the following--uneven bud break, delayed bud break, malformed flowers eg lacking stamens etc.
Yes, it has been the warmest winter on record but that relates to maximums. I think with the clear night skies we experienced, the minimums would be on target for chill hours.

Time: 31st August 2013 2:17pm

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GardenAustraliaWanabee says...
Yry, some chill models subtract hours above a certain max (16C?), so maximums have some impact, however imprecise it may be

Time: 31st August 2013 2:38pm

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Mike says...
http://informedfarmers.com/do-you-know-your-chill-hours/
7c is the threshold temp. below which accumulated chill hours are measured. There are a few models but there doesn't seem to be the latitude suggested above.With lychees you wouldn't call it chill hours you would just say hours below 10c.

Time: 31st August 2013 7:23pm

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Brain says...
Actually, it was the Lapin Cherry that's breaking bud - sadly leaves only and no flowers. Stella has one green leaf, otherwise dormant and Simone is dormant.

Tropical Anna apple is starting to flower, all other apples (the common varieties) still have green foliage from the winter.

Tropical Nashi has broken bud with green foliage, Ya Pear Nashi is dormant.

Prunus Mume - seems to be ever green.

Almond (just acquired and planted) still dormant.

In short, if you live in the subtropics and like to have lots of hope and despair, grow some stone fruits.

Time: 2nd September 2013 11:46am

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yry says...
I've read that better results are to be had if the grower defoliates the tree in winter with 20 per cent urea.

Time: 2nd September 2013 4:38pm

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vlct says...
Minnie royal and royal are not low chill they both require 800 +


Time: 3rd September 2013 9:20am

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Brain says...
I saw a youtube clip many many moons ago, where a lady in California growing Minnie Royal/Royal Lee on the pathway and it was doing well. It does add weight to MR/RL being able to cope with warmer climates. I think some folks in WA has gotten their hands on them last year, so has anyone got anything to report?

Time: 3rd September 2013 10:09am

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About the Author Brain
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BJ says...
They are low chill. Check out Dave Wilson site. 200-300 hours each. Others in the Royal series need around 700hrs though. Royal Rainer only needs 500. MR/RL have great reports from SoCal zone 10a and b, but they do get a bit colder than we do, even through are zone is the same, and they are much drier. I've not heard wonderful things about them in Florida, which is probably closer to our true climate, but I've not heard from many people trying them there... I have heard they do fruit in south Florida, but Cuban May beetles make it not worth the hassle, which is a problem we don't have...

Time: 3rd September 2013 11:14am

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