Citrus Growers Forum

ivica · Posted: Tue 22 Dec, 2009 5:53 pm

Two informative articles about Hardiness:
"Cold Hardiness in Citrus as related to Dormancy"
http://www.fshs.org/Proceedings/Password%20Protected/1959%20Vol.%2072/61-66%20(COOPER).pdf
(Note for Administrator: URL tags do not work here))

"Cold Hardening in Citrus Stems"
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC541864/pdf/plntphys00151-0088.pdf

When we read that Meyer Lemon is cold hardy down to -5C what that realy mean?
Temperature of -5C at 2 meter level or...?
Which duration of such low temp is assumed ?
Is any damage allowed, no defoliation at all or...?

I want know how hardy is the unknown Lemon variety shown at:
link
What a layman like me can do?
Here is report of my try.
------------------------------------

Under test::
Lemon grafted on branch of P. Trifoliata, photo 2009-10-14:

Environment::
Looking toward NNE

Shading net (used as windbreak) is 8m away from the graft.
BTW: Notice my "zone 7b fig" tree on the right.

Looking toward North

Weather Report Field (official for the county) is 50 meters away from the graft and data obtained there will be used in this test.
More info about local climate conditions (not exact but close enough) can be read from here:
http://www.wunderground.com/history/airport/LDZA/2009/12/22/MonthlyHistory.html
That location is airport about 30 km away.

Monthly photos:

Cold Wave Setup:
---------------------
2009-12-14, Monday.
Cold wave approaching. Cold Frame built arround graft under test.

Christmass Light Rope put in there to be used as heater when needed.

2009-12-17, Thursday.
Forecast night before was calling for only -6C in the morning (so I took no meassurements that night)
but we got -8.8C at 2m level and -15C at 5cm.

What happened that night (and the whole week) can be seen here,
Scanned Thermograph for the week 2009-12-14...21:

No temp above zero there.

Temp difference Outside vs. ColdFrame could be about 1C.
I don't know how much (lower,upper bound in degrees) Poncirus Trifoliata as rootstock contributes to hardiness.
However, I think that the graft has been chalenged enough and I should play safer from now on.

2009-12-18, Friday.
At 1 AM heater is turned on for the first time.

Synoptic:
Hour T2m (C) ColdFrame 0.7m (C) Heater
----------------------------------------------------
2009-12-18 01 -- -4 off -> on_10
2009-12-18 05 -6.2 +2 on_10
2009-12-18 07 -5.7 +2.5 on_10 -> off
2009-12-18 08 -- -3 off
2009-12-18 12 -- -- west side opened
2009-12-18 17:30 -- -5 off -> on_10
2009-12-18 18 -- -2 on_6
2009-12-18 20 -9.7 -5 on_6 -> on_10
2009-12-18 21 -10.2 -2 on_10

2009-12-20,Sunday
Termometer reading says -5.5C, time to turn heater on:

Termometer has been setuped so that it can be pulled out (and pushed into) of the frame w/o opening side.

I did ColdFrame inner temp test today.
Meassuring temp difference in heated ColdFrame at 5 cm and 70 cm level in several ocassions I catched this:

70 cm 5 cm
2009-12-20 19:30 -5. -10 ; 5 C degrees difference
I must put more attention to the heat distribution and heat gradients (heater on/off) next time.

2009-12-21,Monday
Cold wave is at its end (this morning we had -16.6C at 2m, -19.8 at 5cm), experiment ended -- awaiting consequences,
time to feed fishes.

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ivica · Posted: Fri 12 Mar, 2010 8:23 am

Main experiment ended 2009-12-21 with morning min temp of -16.6C at 2m, -19.8 at 5cm.
"Heat" wave followed that cold wave, here is synoptic of max temps:
date max temp (2m)
-----------------------------
2009-12-21 5.0 C
2009-12-22 8.9 C
2009-12-23 19.6 C
2009-12-24 19.9 C
2009-12-25 22.4 C
2009-12-26 9.8 C
2009-12-27 6.5 C
2009-12-28 5.6 C

Photo 2009-12-28 #1:

Photo 2009-12-28 #2:

Thermograph Sheet for period 2009-12-29 - 2010-01-04:

Thermograph Sheet for period 2010-01-04 - 2010-01-18:

Photo 2010-01-12:

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Skeeter · Posted: Fri 12 Mar, 2010 12:18 pm

Nice work! Well documented. It will get more difficult as the tree gets bigger. I have decided I will probably have to keep my lemon tree a little smaller than it is now so that can still provide a complete cover.

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Skeet

danero2004 · Posted: Sun 02 May, 2010 7:30 pm

I have 2 poncirus in my garden and they survived a critical -23 C so probably the poncirus has something to do with the hardiness of the graft

Well done

serj · Posted: Wed 20 Oct, 2010 2:48 am

Danero, what is the place where you live? I want to see the weather archive.

Lemandarangequatelo · Citruholic Joined: 01 Mar 2010 Posts: 483 Location: UK

Great work Ivica, I'd also be interested in the answers to those questions. I have a potted eustis limequat sitting outside in my garden unprotected. I read they are cold hardy to -6C, but does that mean no damage at all at that temperature? We had 1C last night and Saturday night and there was no damage at all.

danero2004 · Posted: Wed 20 Oct, 2010 8:48 am

I live in city IASI country ROMANIA zone 6A-B

ivica · Posted: Sun 28 Nov, 2010 8:42 am

Thank you all for comments.

Skeeter wrote:

...It will get more difficult as the tree gets bigger...

Oh yes.
I'll need a lot of luck in future as I had so far:
1) The first graft growth was simply blown off by hail in July. Graft got no direct hit. The resulted growth is from 2nd bud, activated a week later.
2) During dull period in February graft has been left uncovered and forgotten. In the morning when cold returned I jumped from the bed and run out to check what was min temp that night. Temperature droped to -6.1 C only.
3) In the spring I've found a lot of tunnels over PT tree roots area. Mole was there even before I put PT there, I can live with that. But this spring Vole was there too. I had to dig up and bury about 2 m of approaching tunnel built by vole (Microtus arvalis). That resulted in reallocation of vole's feeding place.
Local vole is a very cute creature, check this photo to see what I'm talking about (not my photo, taken by someone 50km away):
http://www.fotke.hr/s-107619-mis-ili-voluharica.aspx

Skeeter wrote:

... I have decided I will probably have to keep my lemon tree a little smaller than it is now so that can still provide a complete cover.

My way to go as well, a shrub.
Shrub form, up to 1.5 m tall (I don't want sacrifice upper canopy of PT tree) will be easier to protect.

Let's close the winter 2009/10 report with this photo

Not even one of mature leaves lost!

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ivica · Posted: Fri 03 Dec, 2010 9:30 am

danero2004 wrote:

I have 2 poncirus in my garden and they survived a critical -23 C so probably the poncirus has something to do with the hardiness of the graft

We were often told that PT will give some hardiness to scion.
How much (lower...upper bound in deegrees) seems no one knows.
Is that correct ? Is anyone aware of a scientific work relevant for it and which can be cited here ?

Let's differentiate between 2 types of grafting:
1. Classical one, using PT as rootsock.
2. Host type (beware, my terminology Wink

) where scion is only hosted by PT and integrity of PT is preserved. That is what I have in this experiment.

I got information (private corespondence) that graft technic similar to type 2 above is used in former USSR to grow apples from south more north.

So, maybe even more hardiness for citrus can be achieved that way.
Again, how much (lower...upper bound in deegrees) seems no one knows.
All we have are a rumours.

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Sylvain · Posted: Fri 03 Dec, 2010 11:02 am

I think I read some where 2°C for low grafts and more for high grafts.
The higher the graft, the stronger is the effect.

ivica · Posted: Fri 03 Dec, 2010 11:50 am

Sylvain wrote:

I think I read some where 2°C for low grafts and more for high grafts...

2°C fits "a few deegrees Fahrenheit" which I saw somewhere in advertisement of a nursery offering cold-hardy dwarf citrus...
("dwarf" above probably implies Flying Dragon as rootstock)
Advertisements are not reliable sources of information but we don't have much choice anyway...

Sylvain wrote:

...The higher the graft, the stronger is the effect.

That could be consequence of temperature distribution by height 0..1m.
In cold nights (winter, frost...), temp difference between 5cm (the coldest) and 2m above ground of a 3..4 degrees of Celsius is nothing unusual, hence "the higher is better". That distribution is non-linear and the biggest increases are in lower parts.

Googling:
http://www.steffenreichel.homepage.t-online.de/Citrus/lime5.pdf
On page 3: "Only if the scion is very cold-hardy, in example Satsume Mandarin scions, Poncirus trifoliata enhances cold hardiness."

BTW, not On-Topic but interesting read:
"Cold tolerance and vigor of young citrus trees on various rootstocks"
http://www.fshs.org/Proceedings/Password%20Protected/1963%20Vol.%2076/105-110%20(GARDNER).pdf

EDIT #1: More information here
"Swingle? Flyin Dragon? P.Trifoliate? What's a poor Citrus..."
link

EDIT #2: Interesting discussion here
"looks like the very first freeze got my brown select satsuma"
link

buddinman wrote:

In the winter of 2009-2010 trees in our area that were on Carrizo and sour orange were killed, including the root stock.

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ivica · Posted: Fri 17 Dec, 2010 7:39 am

Lemandarangequatelo wrote:

Great work Ivica, I'd also be interested in the answers to those questions. I have a potted eustis limequat sitting outside in my garden unprotected. I read they are cold hardy to -6C, but does that mean no damage at all at that temperature? We had 1C last night and Saturday night and there was no damage at all.

This winter is harsh in UK, I hope your tree is well.
It's a year since this thread has been opened and we still do not know even definition of cold hardiness for citrus.

What follow is loud thinking with some handwaving involved Smile

My main concern for now is related to temperature and I'll assume that other factors like wind, sun... are kept out of equation.
I see several interesting check points:

1. The tree itself
1.1 Cold hardiness
Minimal temperature causing no significant tree damage.
1.2 Defoliation
Temperature causing defoliation but no significant die-off.
1.3 Die-off
Temperature causing significant die-off, possible even fatal.

2. Young parts and fruits
2.1 Young growth
2.2 Flowers
2.3 Fruitlets
2.4 Fruits

Lot of things to do, spaning 5 years at least./handWavingOff

Summary of my first test related to the cold hardiness of the tree itself:
During the main period of cold attack graft under test passed through
80 hours of temperature bellow 0 degrees Celsius
10 hours of temperature bellow -5 degrees Celsius
5 hours of temperature bellow -7 degrees Celsius
Freeze was continuous i.e. no thaw events in that period.

Aftermath, March 2010:

Even young top growth of P. Trifoliata had a hard time.
Not even one of mature leaves lost on the lemon graft under test!

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Lemandarangequatelo · Citruholic Joined: 01 Mar 2010 Posts: 483 Location: UK

Wow that lemon you are testing is very hardy! My limequat had about 3 days of 0C weather with 3 nights of -1 to -4C, and in total for about a week and half the temperatures were around freezing. The 3 half size immature fruitlets were damaged and died. The leaves are all drooping and browning. The top leaves are dry and crunchy.

The tree is now kept at no less than 5C and will hopefully not die. Looks like the duration of the cold was what did the damage. Limequats are supposed to be able to take -6C. What this means I don't know. I guess it means -6C for only a few hours one time only, and then back to above freezing.

Keep up your great work, hopefully you will find the answers.

ivica · Posted: Fri 17 Dec, 2010 4:44 pm

Maybe, with a time, Wikipedia will become good source of plant/citrus related information. There are two stub articles:
http://en.wikipedia.org/wiki/Hardiness_(plants)
http://en.wikipedia.org/wiki/Cold_hardening

Preconditioning (hardening) trees prior cold attack is process important on its own.

One more old but good read: "Cold tolerance and freezing point of citrus seedlings"
http://www.fshs.org/Proceedings/Password%20Protected/1963%20Vol.%2076/70-44%20(JACKSON).pdf

Read "Don's Cold Hardy Citrus Blog": "More Citsumaquat Winter Testing 2010-2011"
http://hardycitrus.com/2010-10-30/more-citsumaquat-winter-testing-2010-2011
Edit 2011-01-12: Above link seems to be broken.

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Millet · Posted: Fri 17 Dec, 2010 9:32 pm

There is no exact temperature for the hardiness of a citrus variety. There is only a hardiness range. The temperature at which a citrus tree is damage, due to cold varies, depending on the the weather conditions that existed prior to the freeze event, the length of the freeze event, the low temperature during the freeze event, the time of year, and lastly the variety of citrus. Therefore in one freeze a citrus can survive in good condition, and on another freeze event at the very same temperature, the tree and be damaged or killed. - Millet (758-)