Chill factor (forum)

mgoul131 starts with ...
We live in SEQ supposedly subtropical but the average winter minimum is 8C according to the BOM. Using a chill factor guide this is equivalent to 1100 hours which should allow us to grow heritage apples, pears, cherries etc. These aren't grown around here so am I missing something? Is there more to it that the chill factor guide is telling me? I would love to be able to grow heritage fruits.


Time: 25th April 2018 6:21pm

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Fruitylicious1 says...
Hi Mgoul

You are not far from the truth. I went to BOM website and gathered your monthly average temperature data. Your coldest month Is July where the min is 8.0C and the max average is 17.1. The Formula for computing the chill factor is: min + max /2 and the sum has a corresponding chill factor figure which applies to your area. In my calculations 8c min + 17.1c max = 25.1 /2 = 12.55 = 600 chill hours not the 1100 that you were presuming. But 600 hours is still considered medium to high chill hours hence according to this data you can grow most high chill plants in your area. Why not many people are planting high chill flora in your area is hard to understand. Maybe you can start a new green revolution in your place. Maybe they just need a catalyst like you to kickstart some high chill mini orchards in Witheren, Qld.

For better understanding of the chill units with plants there is a crash course for beginners at www.plantnet.com.au/plantnet-chill-guide/

Happy gardening :-)


Time: 26th April 2018 3:37pm

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Original Post was last edited: 26th April 2018 8:15pm

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brad16 says...
I think 'high' chill is a little optimistic. 'High' chill usually refers to 'reliable' chill greater than 750 hours.
Fruity's estimate of 600 hours would be closer than your original estimate of 1100, but I think it would still be optimistically high.

These formulae are general estimates that have been derived from different climates than you have in SE QLD. The minimum and maximum temperature values change at different rates.

In cooler climates (where traditional 'chill hour' fruits and these formulae originate), the winters start sooner, and spring starts later. Also the chill temperature occurs earlier during the night and the temperature doesn't rise as fast when the sun comes up. Also the sun sets earlier, and rises later in southern latitudes. It may not sound like much, but it adds up.

So yes, it may get cool in the early hours of the morning, where a particular minimum temperature is recorded, but the amount of time that temperatures loom down in the necessary 'chill' range is where you miss out.

I would guess your chill hours are closer to 300-450. I come from Oberon (near Bathurst NSW), currently live on the NSW Central Coast, have a property in NE NSW not that far from Daley's, a property near Kingaroy QLD and another out near Longreach QLD. A single 'chill hour' formula wouldn't get it right for all of these, based solely on minimum and maximum temperatures. The rate that the temperature changes and the duration that they stay there differs from place to place.

There are unique areas like Tenterfield and Stanthorpe that do get sufficient chill hours to grow fruit, like cherries, but they are unusually dislocate from the traditional chill areas of southern NSW and VIC, and are pretty much the northern extent of what you could expect for something 'high chill'. Compare your climate with that of Tenterfield, or even Toowoomba or Warwick (which I'd regard as too warm for 'high chill').

Another indication that high chill is an over estimate, is that your reported average minimum temperature is 8 deg C. 7 deg C is commonly regarded the temp to reach for chill. So your average is borderline, and you'd be relying on temperature below average to contribute significant 'chill'.

Good new though, is that you didn't specify 'high chill' you only asked for 'heritage fruits'. Not all heritage fruit varieties require high chill. Another plus is that, from your location, I assume you have space for a reasonable size orchard. If you are reasonable with your expectations, there is nothing stopping you planting varieties that may be borderline with regards to chill hours. It may be that some years you get some fruit and some years you don't.

All the best with what ever you decide.

Time: 27th April 2018 10:57am

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Original Post was last edited: 27th April 2018 12:31pm
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Fruitylicious1 says...
Hi Mgoul

I agree with Brad thAt there is more to chill hours factors than just simple formula and general statistics.

In my opinion the best way to find out the suitability of high chill fruit trees in your area is to plant one or two for yourself and see what happens. Rather than reminiscing later on 'what could have been if'. At least you will have peace of mind if you find out the answer yourself by doing a field trial.

Happy gardening :-)

Time: 28th April 2018 2:31pm

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Original Post was last edited: 28th April 2018 2:32pm

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mgoul131 says...
Thanks Brad16. I thought I was missing something. As you say there are still a number of trees that are possible even though high chill is not an option. I already have 200 fruit trees, mixed native, tropical and temperate low chill. Guess I was being greedy.


Time: 28th April 2018 4:09pm

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mgoul131 says...
Thanks Fruitylicious for your answer too. I think it gives me a more realistic view anyway.


Time: 28th April 2018 4:11pm

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brad16 says...
I'm growing apples, pears and cherries in NE NSW, but they are pretty shy in producing fruit, or even blossoming.

One of the pears put out a dozen or so fruit this season, but it was one of the trees that I lost track of (I planted most of them without keeping any records other than a list of what was there).

The list of pears in that orchard is:
Doyenne Boussoch
Doyenne de Comice
Josephine de Malines
Marie Louise d'Uccle
Packham's Triumph
Williams bon Chretien
... along with a couple of Nashi cultivars that I also lost track of.

They're still rather juvenile. I planted them a couple of years ago and I think the one that produced the fruit I was talking about was either Josephine de Malines or Marie Louise d'Uccle.
I'm adding more pears to that orchard because I love pears. If they produce fruit, then I feel really happy. I'm adding:
Beurre Bosc
Beurre Superfin
Ducchess d'Angloueme
Durondeau
l'Inconnue

The apples in that orchard are:
Andrea Sauvage
Belle de Boskoop
Braeburn
Bramley's Seedling
Calville Blanc d'Hiver
Court-Pendu Plat
Cox's Orange Pippen
Cripp's Pink (Pink Lady)
Egremont Russet
Esopus Spitzenberg
Fameuse
Fuji
Granny Smith
Graventstein
Jonagold
Lady Williams
Lord Lambourne
McIntosh
Ribston Pippin
Saint Edmund's Pippin
Spartan
Stayman's Winesap

The apple trees get eaten by the kangaroos and wallabies. Surprisingly they still struggle along and I don't even bother looking for buds or fruit, because it's an exercise it futility. Maybe when they grow to a size that is out of reach of the foraging wildlife, I'll start keeping a stocktake of them.

I only have two cherry varieties:
Burgsdorf
Lapins

They have blossomed, but not set fruit. I did give a friend a cherry tree (think it was Stella) many years ago. They said they planted it near Maitland (Newcastle NSW), and one or two years later found 'a' cherry on it.

This year I'm also adding a few more cherries out of delirious optimism for a few festive cherries at Christmas time (a bowl of cherries = Xmas spirit for me):
Bing
Blackboy
Merchant
Sunburst
Ulster

Apparently, Sunburst would be one of the better options if you're bean counting your chill hours.
My cherries are planted in a gully to hopefully benefit from the cold air sink at night. Again, the wildlife has their eye on them also.

Of the apples, pears and cherries, I think the main reason that I've only seen fruit on the pears, is that the pears came as larger, more established trees when I purchased them as bare root. They are now a little taller than me (a little over 2 metres), whereas the apples are still around waist - chest height. So when the wildlife forages, they hit the ones that are easiest to reach. To be able to tell which varieties do better than others near the NSW/QLD border, I'd really have to wait until they are much more mature and out of reach of foraging wildlife.

Time: 28th April 2018 5:06pm

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echinopora says...
We’re in tweed heads and have problems with low chill injury. Nothing dying but sunraycer, angel suptropical and plantnet “nectacot” never really go deciduous and will bloom sporadically from April until fruit finally sets in spring. Stripping leaves late winter seems to help a bit but angel subtropical doesn’t set well. Low chill apples also flower a few times a year and show some low chill symptoms (apical tufting) but if an apical tuft is inhibiting but break pruning it off seems to let some spurs develop. The subtropical fruits definitely yield more and have less disease, even shy bearers like soursop are giving me more kg/Sqm than the apples

Time: 29th April 2018 8:18am

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