Mark from Texas,
your freeze in 2018 is a blessing in disguise. Probably better for the trees that survived near death experience. Now, they are acclimated to it and can probably go thru many more cold freezes later on.
Well, the 18F must have been very short cause every one of the trees that made "is not cold hardy".
Glad my trees can't read.
I need to emphasize again that what induces cold hardiness is:
1. Being well watered and acclimated to the extreme cold for a day or two before the big one hits,
2. Older, dark woody bark
3. Dormant - no plant food months prior.
4. "Warm" micro climate. What helped me was a micro climate induced by a thick low hanging canopy and a very thick mulch of pine needles and leaf litter. I rake the leaves and top off my mango, avocado, citrus beds with them. This very important "natural" forest condition is too often ignored by gardeners.
I pity the avocado grower that has to have the "clean" look under and around their trees.