[NAFEX] Cold Hardy Citrus

philip sauber mrtejas at lycos.com
Sun May 11 08:15:43 EDT 2003


I am intending to submit this to POMONA with pictures:

“Cold Hardy Citrus”

Several people from the Seattle, WA area have contacted me interested in growing citrus in the ground.  After all they are in zone 8(northern) aren't they?  Hmm.  They have been reading about cirus covered with snow and thriving in zone 7!  The morton citrange tastes like a tangleo and can be eaten out of hand!  You can make marmalade from trifoliate orange fruit!  There are not many sources of information available describing how the fruit of citrus rootstock varieties ("cold hardy citrus")  tastes as few people are actually brave enough to taste one.  

To my taste, the thomasville citrangequat is the closest of the "cold hardy citrus" hybrids to edibility.  However fruit from the seedling tree I have tastes horrible so I found a better selection and grafted it to my tree. The juice from my seedling thomasville could not be sweetened with any amount of sugar.   However, even with the better selection of thomasville, most people wouldn't eat it.   I have heard some of the amateur citrus hybridizers of Houston say "there are cold hardy citrus and there are good tasting citrus but there are no cold hardy good tasting citrus."

I have tasted many "cold hardy" citrus fruit at the Galveston county citrus show held in December.  I have yet to taste one that the average person would eat willingly.  After tasting a rangpur lime my wife rushed to the drinking fountain desperate to get the lingering bad taste out of her mouth.  One of the fruit judges at the show told me that most of the various cold hardy hybrid citrus he has tasted would make you gag.  I have tasted the carrizo citrange, ichang lemon, rangpur lime, and many others and they were either too sour or without citrus flavor.  The changsha mandarins I have tasted gave you a mouth full of seeds with every bite.  Trifoliate orange fruit is definitely inedible and one would be dreaming to think you could make marmalade with it, it is so full of seeds there isn't a teaspoon of pulp per fruit!

My experience with citrus cold hardiness:  I had a mature satsuma mandarin and nagami kumquat in the ground in 1989 when the Houston, TX area (zone 9a) experienced freezing weather for 96 hours with a minimum temperature of 10F, a 100 year freeze for our area.  This freeze killed both trees deader than a doornail, even the rootstock never recovered.  It was below freezing for 96 hours with lows to 10F. In that freeze all citrus trees that were not banked with soil were killed including the trifoliate rootstocks. The only trees that survived were banked with soil or covered and heated. I didn't bank my citrus trees in 1983 and 1989 and they were killed rootstock and allKumquat is supposed to be among the hardiest of citrus able to survive 10-15F when dormant.  People in z8 or the warmer parts of z7 may have better experiences with citrus cold hardiness.  If the weather in the winter stays cold without warming up, citrus may be able to better survive cold weather.

Some people claim that grafting citrus as high as 2-3feet above the ground on trifoliate rootstock may make the scion more cold hardy.  This may be true, but grafting high on trifoliate makes it impossible to bank soil to above the graft to protect the tree from freezing in severe freezes. I bank my trees every winter now. I take nursery pots, cut a slot in it, center the pot on the tree trunk, and fill the pot with soil. My one tree (grafted by a friend) with a 2 foot high graft required about 4 pots stacked on top of each other to protect the bud. Banked trees are damaged but not killed by severe freezes and recover quickly even though most of the top is killed. The biggest problem with citrus going into dormancy here in z9a is our unpredictable weather. It may be 85F one day and freezing the next in January and February. In March of this year it was in the 80F for several weeks and then we had a freak 19F low around March 15. Unprotected meyer lemon trees were killed. My unp
rotected meiwa kumquat on trifoliate was killed and a long huang kat mandarin was damaged. The protected trees had damage but survived. Phil 

For the z7/8’ers wanting to grow citrus in the ground:  I went to the University of Washington in Seattle (z7/8) for 4 years and remember that Frosh pond froze over solid for several weeks one winter.  Hmm, doesn't sound very citrusy to me.  Do you have hot weather in the summer?  Do you have to wear a light jacket at night in the summer?  Citrus won't grow until the temperature reaches 55-60F at a minimum and need 90s weather to sweeten the fruit.  

Citrus can survive prolonged freezing weather if protected.  What do I mean by protected?  You can cover them with a tarp or blankets and put a heater underneath or you can bank the trunk to above the graft with dirt.  The dirt will protect the graft from freezing but the top will be frozen.  When spring arrives, cut the frozen parts away and the top will grow back rapidly.  This is how meyer lemons (hardy to 24F) are protected in my areas.  I have seen mature 15 foot meyer lemons trees banked, the top frozen, t top cut off and by fall be 6-8 feet again to fruit the following year.  We occasionally get a few hours of 18-20F but didn't have that cold of weather between 1989 and 2002.

Citrus trees can survive cold weather for a few hours in z9a if dormant.  Where I live on the Texas Gulf Coast, we often have warm spells on and off again all winter long.  These warm spells can cause citrus to grow actively at just the wrong time because a "blue norther" cold front can blow down from Canada at any time and freeze us out=>dead or damaged citrus trees.  One thing that can help is not fertilizing your citrus trees after June 1.  Without the stimulus of fertilizer, a citrus tree is more likely to stay dormant all winter.  I know of a sweet orange in a vacant lot in Beaumont, TX that has survived some freezes, however it is neglected and gets no fertilizer or irrigation and is close to the Neches river and a Refinery=>maybe a heat island?

Stan of  coastal South Carolina:
I have been growing satsumas for 20 years outside/in ground and have seen some brutal temps in that time period...I do take precautions to  protect my trees when the temps are to be in the low teens but so do the citrus growers in the citrus belt... I pull out the plastic on an average of once a winter...  Not a bad trade off considering the reward I get when my satsuma trees bear a bumper crop.   Agreed, some of the citrus species you describe may not be grocery store quality. Still for someone outside the citrus belt, the sight of a large citrumelo or ichang lemon tree, loaded with fruit is reason enough to grow them.. There is also a tangerine tree of unknown origins that grows here in Coastal SC that I will put up against anything you can grow on the Gulf Coast... This tree bounced back from the Christmas freeze of 86 that wiped out most of the Central Florida groves.. It has been constantly producing fruit since the early 90's and has never been artificially protected in a
ny form or fashion.
 
Stan reports that he is zone 8a, about 60 miles from the South Carolina coast and 240 north of Florida.  He has 4 mature satsuma trees.  His area rarely experiences 24 hours of freezing weather and when they do he covers his trees with plastic.  He is planting a citrus grove on his farm near Scranton, SC 29591 of citrumelos, citandarins, ichang lemon, a row of satsumas and his favorite hardy tangerine.

Larry of Vancouver, BC:
Larry replies at his success after I sent him thomasville and sour orange seeds last fall. All the seeds you sent me did sprout and seedlings are doing great! In fact I planted out some of the thomasville citrangequats into a cold frame to over winter with protection and have kept a number to remain in my greenhouse as well. I'm hoping that I will have a reasonable survival rate on the cold frame seedlings as it doesn't really get all that cold here in the winter but still need to hedge my bets though. .My seed grown Poncirus has finally produced 1 lonely fruit this year after being in ground from seed planted about 8 years ago. Citrus sure does take its time to produce fruit doesn't it! Am also trying a Carrizo outdoors with protection  as well as a Owari Satsuma on Poncirus rootstock... not sure how they will do but we will see. 

John of Lake Jackson, TX with over 100 citrus varieties in his back yard says:

I gave up long ago with the cold hardy stuff and just decided I want good tasting stuff.   I have talked to Dr. Brown (Dr Brown is a citrus hybridizer who has been making crosses for 50 years) and he told me that even with the first cross with trifoliate the cold hardness drops significantly and f2 and f3 away from trifoliate make the tree even more tender.  The other problem is you can not use trifoliate as the mother because it does not produce hybrids.  (There are claims that there is a zygotic producing trifoliate, but I don't know who has it.)

The marginal citrus zone members may contact me by e-mail to request seeds of cold hardy citrus.  I can usually obtain them in the fall.
Phil Sauber
 




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