What to Record Before Calling a Citrus Tree Cold Hardy

A hardiness claim is only as good as the record behind it

If you are trialling citrus where winters are marginal, you will hear hardiness claims constantly: this one took a certain low, that one died at another. A single number tends to travel without the things that made it true or false. Which tree? Grown how? Cold for how long? Did it recover, or did it only look alive for a month?

This article uses one public example to show what is missing when a hardiness number is quoted alone, and then lists what to write down for each tree you are testing. The example is thin evidence: one breeder's note and a few reader comments about one cultivar, on one blog. We are not offering it as a hardiness rating for that cultivar, and certainly not for citrus in general.

What one breeder wrote about one cultivar

The Hardy Citrus blog's post on the Ventura Lemandarin (https://hardycitrus.blogspot.com/2014/06/ventura-lemandarin.html, dated 28 June 2014, read 30 October 2026) includes a note labelled "From the breeder". Read it as a record of two trees, not a rule:

• A seedling on its own roots: "It survived at least to I think 11°F, -12°C degrees and a few 13°F and 14°F, -11 and -10°C events in the past. This winter it reached its max tolerable temp where it died at 5.5° F, -15°C on its own roots."
• A backup graft of the same cultivar: "Less than a foot away I had a back up graft of it on flying dragon about 4 feet up that defoliated with branch die back but is growing back very well."
• The breeder's own reading of that: "when high grafted it can at least withstand about 6° F, -14°C."

Notice how much is packed into those lines. There are two outcomes from the same winter, less than a foot apart. One tree was on its own roots and died; the other was grafted about 4 feet up on a different rootstock and lost its leaves and some branches, then regrew. Remove the context and you are left with two temperatures that sound like they contradict each other.

Cold is not just a minimum: duration matters too

The comment thread on the same post adds a point a single low-temperature figure cannot carry. On 30 June 2019 a reader in Oregon asked where the lethal winter happened, "Just for comparison purposes". The reply on 2 July 2019 gave a date rather than a place: "January 2014. A couple years later it never got as cold but the cold lasted for several days and many Ventura Lemondarins died".

That is one commenter's recollection, and we do not know how many plants or what conditions were involved. But it is a useful reminder of what to log. If the record only captures the lowest reading of a winter, a long stretch of cold days and a one-night dip look the same, and they may not have the same effect on the tree.

The same reply offers advice, again as one person's view: "if a 'hardy' citrus is in zone 8a or colder, plant the tree in a protected place where there is less sun in the winter. Grafting a meter high on Poncirus will also add a few degrees of hardiness." Whether or not that holds for your trees, it points at two things worth recording: the microsite, and the graft height.

What to record for each tree

Treat each tree as its own trial. These fields would have made the breeder's two trees easy to compare, and would let you compare your own:

1. 1Location and microsite. Where the tree stands on your map, what shelters it (wall, hedge, other trees), and how much winter sun it gets. The advice above suggests a protected spot with less winter sun, and you can only test that if you wrote down what each tree's spot was.
2. 2Rootstock and graft height. Whether the tree is on its own roots or grafted, onto what, and how high. The breeder's note mentions "about 4 feet up" and the reply mentions "a meter high"; either way the height is part of the tree's identity, so record it at planting.
3. 3Each cold event, with its minimum temperature and its duration. Date the event, write the lowest reading, and count the consecutive cold days. Say where the reading came from: your own thermometer at the tree, or a station elsewhere. A thermometer near the tree and a distant forecast can differ.
4. 4The injury you saw. Use plain, dated words: leaves dropped, tip dieback, branch dieback to a certain point, trunk damage, dead. Add a photo when you can.
5. 5The recovery. Note whether and when new growth appeared, from which part of the tree (above the graft or below it), and the date you judged the tree recovered or lost. In the breeder's note the high graft was "growing back very well" while the own-root tree was gone, a difference that only shows up if the outcome is written down.
6. 6First flower and first harvest dates. A mild winter that kills nothing is only part of the story if the tree never fruits. One commenter on the same post wrote on 16 April 2020 that their plant "first time blooms now in my backyard (Exotica Tolosa, southwestern France). 7 years from seed." That is one person's report from one garden, but it shows why the bloom date is worth logging, and how long a trial can run before the question of fruit even comes up. The same commenter said they did not yet know whether the seedling came true from seed, so this is not a flowering timeline for the variety.

Why per-tree beats per-site

The breeder's two trees sat less than a foot apart in the same winter and ended up in different states. A note kept for the whole garden would say "cold winter, some losses". A note kept per tree says which rootstock, which graft height and which injury. Over several winters, per-tree notes let you compare individual trees alongside the garden-wide record.

It also guards against two common errors: calling a tree hardy after one mild winter, and writing it off after one hard one without noting how long the cold lasted or whether it was grafted high or low.

A starter template

• Tree: cultivar, rootstock, graft height, planting date, map location, shelter and winter sun
• Cold event: date, lowest temperature, number of consecutive cold days, where it was measured
• Injury: what you saw and on what date, with photos
• Recovery: first new growth date, where it came from, and the date you called the outcome
• Season: first flower date, first harvest date

The source here is one breeder's note and a few reader comments about one cultivar. It is evidence of what to write down, not a hardiness rating. Your own trees, over several winters, are the data that count for your site.

How CanopyTwin fits in

CanopyTwin is built around a record per tree. You can put your trees on a live satellite map, give them QR tags, and keep a tree inventory with photo history (the Grower plan covers up to 50 trees). On the home page, voice notes from the field are described as transcribed and filed to the right tree, which is handy after a freeze when you are walking rows with cold hands. Every plan starts with a 30-day free trial and no credit card is required, so you can set up your trial trees and see whether the record suits you.