I have five citrus in he ground - Kumquat, Thomasville, Satsuma 'Brown Select', Algerian Clementine and grapefruit 'Ruby Red'. All but the Thomasville were planted last year. The grapefruit went in the ground late July.
I'm south of Wilmington, NC on a barrier island. We stay warmer than Wilmington does and have only gotten below 32 four time this Winter. Last Saturday night a cold front came through and Wilmington got snow flurries. We got rain and a teensy bit of sleet. I covered my grapefruit with a sheet, but it blew off in the wind; luckily it only got down to 31F. The next night it reached 28 and the sheet DID stay on (lots of clothespins!). Here's what it looked like Saturday.
I think it held up pretty well!
Barb

Well crap. The picture didn't show. Let's see if I can' figure out how to properly link the picture.
Barb

Hopefully this will work......http://s1293.beta.photobucket.com/user/Beach_Barbie/media/Grapefruit21813_zpsd288d00e.jpg.html

Hi Barb,

The Red grapefruits seem to be fine with short periods down to 28. All of your trees should do well in limited cold except for perhaps the limes. They don't much care for the cold.

Nice list of trees you have, and the pictures are great!

David

The tree is suffering from a mineral deficiency. The leaves are showing the pattern of a Magnesium deficiency, but magnesium deficiencies shows up on the older leaves. The leaves on your tree that are showing the deficiency are the new leaves. The mineral deficiencies that appear on a tree's new leaves are iron and manganese. At this point I am not absolutely 100 percent sure what the exact problem is, but I would think manganese, because the green veins have a broad green boarder on them. You can see that the deficiency is getting worse as you look higher up the tree. You need to get this taken care of before a big problem occurs. - Millet.

My two Rio Red's did fine with 5 days in a row with nighttime temps down between 26 and 28 degrees, very pleased. And Millet is correct - you're seeing what I also believe to be most likely iron deficiency. Looks a bit different than my Manganese deficiency, but it could easily be both, and you'll first see Manganese deficiency quickly followed by iron, based on your soil pH. That, combined with cold rainy weather will cause a locking out of micronutrients. I would apply a micronutient right away. You can use Citrus Grower's Blend either as a foliar application, a soil application or both. I would opt for both. And, I would make sure the pH of the water you use to mix up the solution be acidified just a bit, if your water pH is above 7.0. Just a tablespoon of white vinegar to a gallon of water should be sufficient to bring the pH down. Don't drop below 5.

I'm very impressed that you only got down to 28 degrees, according to the latest USDA zone map, those barrier islands in southernmost NC are in right in the 8a/8b range, which would make grapefruit a short lived tree without serious protection. What kind of lows do you normally experience in your location?

barb,
I'm in Northchase. The last 2 Winters here have been very mild.
This hasn't been the norm. Five or six years ago we had an Easter day in the seventies drop to 18. It killed most fruit buds that were already blooming. I lost several citrus trees.
We had one recent winter that dropped into the teens for 3 or 4 days.
I have found a half a dozen or more rootstocks growing in the Wilmington area that had their scions frozen. I found another one last month. The owner said that it had sweet and easy peel fruit and it lost its flavor. Now that the scion died she has a 15 foot Swingle rootstock heavy with tasteless fruit.
I would like it if it mild from now on. But I don't think so.

Xerarch,
I guess our island didn't read that map! I've been keeping track of our temperatures for over 10 years now. The islands (Bald Head and Pleasure, where I live) are 8b. Wilmington is 8a/8b. I have a tropical hibiscus in the ground here. It needs plenty of protection, but comes back every Spring.
28 is the lowest we've had all year by 3 degrees.
I tried to find a picture of the tree before the cold hit, but don't seem to have one. That way I could see what discoloration was caused by the cold and what is deficiency. Oh well. The pH is slightly acidic (above 6). I'll treat it tomorrow.
Barb

I agree with Dave. My trees planted outside look exactly like this at the end of the winter. It is primarily seen with younger trees that do not have as established root systems. It corrects itself once the warmer weather comes around, assuming you fertilize it appropriately.

-Brett
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The yellow coloration in citrus leaves during cold weather is due to the roots slow absorption, and trans-location of the element nitrogen. When the weather warms, the absorption and trans-location increases and the green coloration returns. This can happen over the course of the winter, but usually does not happen over night after a cold snap. But like Beacbarbie wrote, it would be very helpful if she did have a photo prior the the cold event. Lastly, as I wrote above the deficiency leaf pattern does not seem to fit specifically and clearly to any one deficiency. Perhaps, as Dve and Bett writes it may improve in the coming spring. - Millet

Wow. I'm going to have to keep track of the weather in Cape Hatteras.
I bought a weather station that I can connect to Weather Underground, I just need to figure out how to get it uploaded to the Web. When I do, I'll let y'all know the name.
Barb

My red blush grapefruit didn't show any damage at 24 degrees this year. I don't provide any frost protection. Citrus are much hardier than is generally reported assuming there is time for them to adjust to the cold and the coldest temperatures are relatively limited in length (e.g. several hours overnight).

-Brett