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Author Topic: Accuracy of cold hardiness temperatures?  (Read 83 times)


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Accuracy of cold hardiness temperatures?
« on: January 09, 2018, 06:13:02 PM »
Over the last few weeks thanks to google  I have been reading scans of a variety of older 20th century scholarly works regarding growing citrus, and one of the things I noticed was a significant difference in reports of cold hardiness for various common citrus cultivars.  Not so much the absolute temperature values, but instead their relatively sequence  from most to least cold hardy.    One in particular that I noted, several of these mid 20th century works list Meyer's lemon as being almost as cold hardy as Owari Satsuma, which matches my observation of many people near where I live on the 8b/9a line having mature inground Meyers lemons growing in their yards that get no formal freeze protection yet continue to survive.

All of which leads me to ask, does anyone know of any modern detailed studies on cold hardiness of common citrus cultivars, I know there are many guides published by universities that list the often repeated numbers, but I have to wonder if that is all they really are, since based on comments on this and other web forums there seems to be a dependency in real world observations on cold tolerance of certain types of citrus, particularly Meyers lemons, and certain types of Grapefruit.


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Re: Accuracy of cold hardiness temperatures?
« Reply #1 on: January 10, 2018, 12:33:33 PM »
At best the information on temperatures that a citrus cultivar can survive are general estimations.  Many, many variables contribute to the survive-ability during a cold spell.  Such as----the temperature just before the cold spell, the water content in the root zone, the age of the tree, the thickness of the trunk and branches, the wind, the length of the freeze, the health of the tree, the root stock, and the particular location the tree is growing in.    Grapefruit is generally listed as one of the more tender varieties, but one hears stories of the Dunstan grapefruit, which in reality is not an actual grapefruit, but rather a Citrumelo.


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Re: Accuracy of cold hardiness temperatures?
« Reply #2 on: January 12, 2018, 03:11:21 PM »
Ilya11 had a related post on another thread a week or two ago.  It got me to thinking, and I've spent hours studying research papers on cold hardiness of apples and plums.  Similar papers came up on pears, peaches, and apricots when I searched on google.
So there is an amazing amount of information that  might matter.  Much of it rather discouraging to me, as in breeding hardier citrus, I need to be able to sort out those in each generation that are a degree or two more hardy.
First the good news.  My idea of testing cold hardiness of scion wood works with apples.  Good.
Now the bad news.  For such a test to work, the trees the cuttings are taken from must be from the same location.  And we all know that microclimates can vary even in small areas.  Fertility must be good in the ground where every tree was grown.  Rootstocks need to be the same.  If the cuttings were taken from own-root plants, then root differences may effect twig cuttings.
One study treated freeze damage and cold damage seperately.  Freeze damage is damage from sap freezing in the xylem.  Cold damage is damage done though the sap in the xylem hasn't frozen.  Spring and fall damage is often cold damage, not freeze damage.
I would like studies to be made of cuttings, scionwood-like cuttings, of different varieties and different species of citrus from different locations, tested different times during spring, winter, and fall.  I think the resulting data would be quite useful.  A little dorm-type refridgerater would be enough to test twigs of several trees at once.  I think a couple of days might be enough to test freeze damage at a given time and place.
Testing for tolerance to quick drops in temperature, then the temperature going right back up, like single overnight freezes, will be harder to sort out.


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