The relatively surprisingly bad Southeast Texas freezes of January 6th and 7th, 2017, left many of us wondering how our semitropical fruit trees have done. There are really three questions:
(1) The first is relatively obvious: were they killed and if not how bad was the damage?
Questions (2) and (3) are potentially more important since they help us learn.
In the 1980’s, Stewart Nagle, Ph.D. did a careful assessment of citrus damage after the very destructive 1983 and 1989 freezes where temperatures in most places were near the all time records. He went all over the southern half of the state looking at what survived and why. He developed many generalizations about what happened including what did well in freezes and what did poorly. And most of his findings and of course those of many others across Texas and the world are what we use today for good guesses.
As I remember it, he said that for most citrus, their survival depended on several factors:
(1) genetics–kumquats, yuzu, trifoliate, mandarins hardy; pummelos, citron, limes less so.
(2) rootstock–trifoliate and tf crosses: hardiest; sour orange, rough lemon: not so.
(3) active growth– quiescent & healthy: hardy; but active growth or diseased: tender
(4) hours below particular temperatures: less than 32˚F,less than 28˚F, less than 25˚F,less than 22˚F, less than 18˚F, less than 14˚F, less than 10˚F
(5) size of wood killed: leaves only, new growth, twigs, branches less than 1 inch; branches more than 1 inch; trunk; whole tree
To this I would add another factor: exposure
(6) orchard trees exposed to winds out of the north, to winds from the east or west, or overhead are not as sheltered as many house yards where buildings and other trees can provide some warmth protection.
In today’s world with an electronic network across Texas and beyond, it is possible to use this information to learn what caused the damage to your trees. It is also possible to share your conclusions, provided you report the information above for your site to develop a profile of how different fruit trees behaved in various locations and temperatures. This would allow us to understand just how well mangoes and lychees did too.
If you want to do this systematically, you should assess at least twice–at 2-6 weeks and again in about 6 months. Plants on their own roots like some lemons may take even longer to show life.
I have included below an Excel File you can use to do an assessment. freeze-report-template
You could also fill it in in handwriting so there is also a PDF you can download and print.
I have completed my assessment of orchard trees and will post this here so you can see an example when it is available for upload.