Wednesday, November 12, 2014

How Much Cold Can Your Citrus Trees Handle?

We are entering the shivering season for the Central Valley, Bay Area and low foothills. Late November through mid-February is the most critical time here for protecting frost-susceptible plants.


Frost Cloths Protecting Lemons, Mandarins, Oranges



This is especially true for citrus tree owners, who are anxiously keeping an eye out on the upcoming weather forecasts.







Several days before an expected frost (temperatures dipping down to 32 degrees) is the time to gather the necessary implements to protect your citrus trees, including giving the ground beneath them a good soaking (moist soil is better than dry soil at moderating the temperature beneath the tree).

Most gardeners first thoughts about protecting their citrus trees during a frost or freeze is, "protect the fruit!"

Four Winds Growers, the Winters-based wholesale grower of many excellent varieties of citrus, offers the Citrus Variety Information Chart at their website, FourWindsGrowers.com

Included in that chart is extensive information about each citrus variety, including suitability for indoor growing; its bloom and fruiting seasons; its recommended summer heat level to produce good fruit; and, its minimum tolerable temperature for preservation of fruit quality.

  The chart points out that lemons, limes and citrons are most sensitive to frost, while sweet oranges, grapefruit, tangerines and calamondins are intermediate. Kumquats and Owari Satsuma Mandarins are the most frost-tolerant, braving temperatures into the twenties (that would classify as a freeze).

From that chart, here are the temperatures (in degrees Fahrenheit) at which citrus fruit damage may occur. 

Sweet Oranges
Washington Navel Orange  28 
Trovita Orange  28 
Cara Cara (Pink) Navel Orange 28 
Lane Late Navel Orange  28 
Robertson Navel Orange  28 
Shamouti Orange (Jaffa Palestine)  28 
Valencia Orange  28 
Midknight Valencia Orange  28  

Blood Oranges
Moro Blood Orange  28 
Sanquinelli Blood Orange  28 
Tarocco Blood Orange  28 
 
Sour Oranges
Bouquet De Fleurs Sour Orange  28 
Chinotto Sour Orange (Myrtle-Leaf)  28 
Seville Sour Orange  28 
Bergamot Sour Orange  32 
 
Mandarins
Gold Nugget Mandarin (Patented)  26 
Tango Mandarin (Patented)  32  
Owari Satsuma Mandarin  24 
Dancy Tangerine  32 
Clementine Mandarin (Algerian)  28 
Murcott Mandarin  32 
California Honey Mandarin  32 
W. Murcott Mandarin  32 
Kinnow Mandarin  32 
Kara Mandarin  32 
Page Mandarin  32 
Piie Mandarin  32 
Kishu Mandarin  32 
 
Lemons
Improved Meyer Lemon  32 
Eureka Lemon  32 
Lisbon Lemon  32 
Ponderosa Lemon  32 
Variegated Pink Lemon  32 
Yen Ben Lemon  32  

Mediterranean Lemons
Villafranca Lemon  32 
Genoa Lemon (Gea)  32 
Limonero Fino Lemon  32 
 
Limettas
Millsweet Acidless Limetta  32 
Marrakech Limetta  32 
 
Limes
Bearss Seedless Lime (TahitiPersian)  30 
Kaffir Lime (KiefferThaiWild)  32 
Meican Lime (Key)  32 
Thornless Meican Lime  32 
Meican Sweet Lime  30 
Palestine Sweet Lime  30 
Rangpur Lime  32 
 
Grapefruits
Oroblanco Grapefruit  32 
Rio Red Grapefruit  28 
Star Ruby Grapefruit  28 
Chandler Pummelo  28 
Cocktail Grapefruit  28 
Chinese Grapefruit  28 
Melogold Grapefruit  28 
 
Kumquats
Meiwa Kumquat  28 
Nagami Kumquat  24 
Indio Mandarinquat  26 
Centennial Variegated Kumquat  30 
Nordmann Seedless Nagami Kumquat  28 
Marumi Kumquat  26 
Eustis Limequat  32 
 
Citrons
Buddha's Hand  Fingered Citron  32 
Etrog Citron (Ethrog)  32 
 
Other Interesting Varieties
Minneola Tangelo  28   
Australian Finger Lime  32   
Yuzu  24   
Calamondin  32  
Variegated Calamondin  32

But what about the overall health of the citrus tree? How low can temperatures go during a freeze event before the tree is toast? 

 "I consider 22 degrees to be terminal for citrus tree cambium cells," says Cedar Seeger of Four Winds Growers. The cambium layer is the growing part of the tree, the cells that are producing new wood and healing wounds. It is located just beneath the bark.

And that's for a citrus tree in tip-top shape: good health, with moist soil around it during a freeze. Cedar uses the example of a Meyer lemon tree:


Blanket + Tomato Cage for Citrus Protection
"We often have a two to three hour dip to 28 degrees after storms; and if the above conditions are met, even Meyer lemon trees can survive, albeit not to happily, without protection. 28 degrees for four hours probably won't kill the tree, provided the rootstock cambium doesn't freeze. It will defoliate and lose twigs. At 24 degrees things start to get dicey. That's when the blanket, frost cloth, bonnet and/or the old-style, large outdoor Christmas lights that give off some heat will work wonders. Remember, those blankets and bonnets need to go to the ground in all cases."






Chandler Pummelo, Pummeled by 2010 Freeze



You may recall Thanksgiving Week of 2010, when morning low temperatures dipped well below freezing for six days in a row, led by a citrus-killing 27 degree morning on Thanksgiving.








When a large, cold-air mass moves in from the north after a storm in the winter, that is called an advective freeze. The one that sticks out in most gardeners' memories here was the freeze of mid-December 1990, when nighttime temperatures fell into the teens for several days in a row, with a couple of days that didn't climb above 32 degrees. To add even more injury, a second cold snap hit near the end of the month, with temperatures dipping into the mid-20's. Many of the most susceptible (frost intolerant) landscapes were completely lost; some nurseries never recovered.

"Our first year in the citrus business here in Winters was 1990-91. My wife, Mary Helen, and I have a Masters in Disaster," says Cedar Seeger. 

Which is why Cedar is an adherent of watching the dew point, the temperature at which saturation has been reached, when water vapor condenses into water. The lower the dew point, the more danger of cold damage to your plants. One good online source for dew point temperatures is the National Weather Service's Tabular Forecast Page  , which offers a forecast for two days in advance (that link is for Sacramento). 

"A good watering going into an advection night is mandatory. If the ground and surrounding grass is wet, it creates a micro dew point environment around the trees. In a dry, cold La Nina winter such as we're about to get, it is important to remember the dew point concept. At 22 and below, it's full on emergency response, pile straw, hay around trunks, anything, lights, covering," says Cedar, a man who learned these lessons the hard way.  But he is not an adherent of running sprinklers during a freeze.

"My experience with overhead sprinklers is that they more often than not freeze up, and then it's all over. And you are risking branch breakage on that ice-entombed citrus. Yeah, it can work, but screw it; it's messy, risky and a lot of work. Use the large Christmas lights and mid-weight frost covers. But pay attention to the trunk / rootstock. If that freezes, it's a goner."


Citrus trees most at risk to fatal damage from a frost or freeze are the young trees. It is vital that they be covered completely when a heavy frost or freeze is predicted, and provide protection for the trunk, bud union and rootstock area. That can include trunk wraps, newspapers, old carpeting. If possible, move small containerized citrus closer to the house, preferably next to a south or west-facing wall to maximize reflected heat.

13 comments:

  1. I use beach umbrellas draped with plastic to protect my dwarf citrus. They come in two parts. The base stake stays planted in the soil during frost/freeze danger. The umbrella portion is collapsed during the day and removed to allow sun. That portion is returned to the base in late afternoon. Sometimes the temperature during the day is so low that the drape stays put. I use clothespins to keep the plastic attached to the umbrella similar to a shower curtain.

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  2. I am hopeful that we are in for a mild and wet winter in the valley. But I did purchase three new C-9 light sets from Emigh's just recently. Last year's freeze really walloped the lime and lemon trees to the point where they either produced nothing or very little in terms of citrus production this year. I'm not going to go through that risk again.

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  3. when I lived in the area I would put large buckets of water all the way around plants that might freeze. I was giving them an extra layer of protection as all the water would have to freeze before the plants would also freeze. I used empty kitty litter pails and old clorox or coffee containers.

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  4. I have a Bearss lime tree that was about 4 years old in a large pot and it was producing really well. It froze all the way down to the roots but came back. It has been two years now and it is now about 3 feet tall but not blooming. Do you think the tree will ever produce again?

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    Replies
    1. If the growth has larger, leathery leaves than you remember...and there are nasty thorns along the stems...it is probably rootstock growth which will probably not bear (pun intended) edible fruit.

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    2. Yep, the leaves are as you say and the thorns are there.. Oh well I guess I will have to go out and buy another. Thanks

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  5. Heya~

    I don't know if you are still able to chit chat, but I recently got a Mandarin Orange. It is in a pot and a pretty small tree and I haven't transplanted it to a bigger pot because I was advised to wait for it to stop fruiting first.

    Recently we had a bit of a cold snap and I had forgotten to bring it in. The tree and branches are fine, still green. But the leaves are dried and curled up. Anything I can do for it? For now I've been bringing it in at night and leaving it outside to get sunlight when it is warm (usually in the 60s/upper 50s daytime, but colder during the night).

    Any advice? This is my first tree.

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  6. I have an orange tree here in Houston that had the leaves described and lots of thorns but no fruit. After 21 years it finally had 3 oranges, the next year a couple of dozen, and this year over 300! I thought it would never fruit, but never removed it. You never know.

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  7. Lemons in Eugene, Oregon? With a bit of effort, one can grow lots of lemons up here but trees need to be covered now and then with a heater as needed. We are 8b here. My 7 foot tree is loaded. I give lemons away.

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  8. Thank you! It's dipping into the mid 30s in Mississippi tonight and I brought all (blooming) limes and blood oranges into the garage. Everyone else is draped in Frost blankets during this cold snap.
    I appreciate your page-very helpful!

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  9. These temperature limits are not accurate. It looks like the same info from Four Winds Growers. For example most mandarins will be much hardier than grapefruits and oranges. Mandarins should be hardy to 20 to 26F. Grapefruits are not as hardy as oranges. Don't rely on these temperatures.

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  10. I live in south Texas and we just suffered a deep freeze that lasted a few days. My mexican lime tree is about 12 years old...too large for me to cover. It has always been very healthy and have me a generous supply of wonderful lines. Right now the leaves have all turned a yellow color. I'm so sad and hoping I have not lost this wonderful tree.

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  11. I live I South Mississippi . I have a prized Satsuma, seedless variety that’s about 7 to 8 feet tall and wide. This Magnificient Specimen produces hundreds of delicious smaller fruits each year!!! We cover it in frost/ freeze times diligently! But there has come a mold/ blight patch to the trunks and limbs… Do y’all know a quick / clean / organic spray for this , please?!? The tree is 20 years old this year , and My Favorite Thing On Earth!!! Any Help Would be Appreciated! Thanks , Chris from Mississippi ! BTW; Thank You All For your Helpful Insights and kindnesses! 🙏🏻🤙🌸

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