It got to 16F in Houston, TX area a few weeks ago for a few hours. Nearly 100% of citrus trees and other semi-tropicals were killed by freezing whether they were “cold hardy” or not. Yuzu, satsuma, kumquat, all dead even though they are the most cold hardy. Most rootstocks like trifoliate were killed along with the grafted tops. “Artic Frost” series, all dead. Worst was the weather the week before the freeze was in the 80s. I didn’t do much protecting since I’ve had satsuma survive for the last 25 years with cold as low as 18F without dropping a leaf and just the occasional cracking of bark or small diameter branches freezing. So 25 inground mature citrus all froze. This cold hardiness is typical for the Gulf Coast area. It is around 30 miles from the Gulf here. Places in the northern suburbs of Houston got a few degrees colder.
Interestingly my friend John Panzarellas mature seedling avocado tree survived. It has a diameter of maybe 20 inches at the base and is only a few yards from Oyster Creek. All branches froze but the stump somehow survived and is sprouting again. Another friends ujukitsu a sweet lemon somehow survived even though his satsumas froze.
This cold hardiness event might have turned out different if it happened in Northern California. They don’t get the wild temperature plunges there like in Texas. Or different in Vancouver, BC where a few grow yuzu in heat islands next to warm house walls and protected. Citrus trees are killed by the absolute low temperatures not the average lows like the USDA zones are based on.
Houston is zone 9a or 8b. But 16F is close to zone 8a(10-15F) lows. Citrus can’t survive unprotected in zone 8a Gulf Coast.
So citrus cold hardiness is a complex subject. It is not enough to say "hardy’ to 16F. The “frost series” wildly claims “hardy to 10F.” Depends on the weather before the freeze and whether it is California or the Texas Gulf Coast. It also depends on the length of the freeze. A few hours of freezing is way different than 24+ hours. I know many living in Dallas, TX were fooled by the untrue cold hardy claims of the “Frost Series.” Don’t believe the claims of the people who are selling you the trees. It usually gets 6-10 colder in Dallas than Houston. We had a long period of no citrus killing freezes from 1989 to 2021. Then freezes in 2021 and 2023 that killed them all.
So if you live more than 30 miles from the Gulf, plan on covering/heating your satsuma trees occasionally or they will freeze. A friends trees in Matagorda froze even though he is only a few miles from the Gulf and on the Colorado river.
Visited a citrus growing friend in Lumberton,TX yesterday. He had 82 trees mostly mature and very large. Most came from me when I lived in Beaumont. 95% look dead and a few might survive even though he protected them by banking. Surprisingly the ujukitsu survived and the satsumas died.
My citrus also froze here near Sugar Land. Most were unprotected but the protected ones froze also.
However, all is not lost even though not much budwood available this year. Over the years I’ve given various friends grafted trees of my favorite varieties as backup. I’ve asked them and most of my favorite varieties have survived by either potted trees I grew or potted ones from various friends. I gave away around 20 large 7 gallon 10+ YO trees after the 2021 freeze because I was tired of dragging them into my garage for freezes. Should have kept them! John Panzarella spent two days dragging potted trees into his garage with the help of high school students as he is 80+ YO now. Scott Johnsguard spent 4 days protecting his trees before the freeze. I was busy with remodeling and didn’t protect as much as 2021. Didn’t cut budwood before the freeze as I didn’t expect it to be as bad as it was. My very favorite sugar belle survived in a pot in a greenhouse. I grew it out from seed and waited 7 years for fruit! Probably next year I’ll get budwood and graft to various rootstock stumps that survived.
Best citrus protection I know of, grapefruit on flying dragon. Couldn’t protect it from salt water however when hurrican came by. Bridge City, TX flooded by several feet of salt water: