Avocado is often described as being heat loving, but nearly every outdoor avocado has started a new flush with the start of the fall rains, and they mostly seem to be growing vigorously despite many nights in the upper 40s over the last month, and even a couple nights below 45°F.
In contrast, all the citrus I’ve got outside has been dormant for a month now.
I noticed the giant Mexicola Grande seedling that I planted out this spring is in the early stages of forming proper bark, so that got me thinking about what the “trunks” of some of the larger trees look like now, both outside (where it may be an indicator of increased frost resistance) and in the greenhouse.
The above-mentioned Mexicola Grande seedling, #37 (this stem represents two seasons of growth, the roots are one year older due to Dec 2021 winter damage):
The Jade graft on a second-year Bacon seedling, planted out this spring:
The hardiest second-year Duke seedling so far out of those tested outside (#149), this stem survived 17°F (-8°C) last winter even more green and tender, with just a flower pot turned over on the tree, so hopefully it’ll be fine this winter too, even if some damage occurs again on the newest growth:
Now some greenhouse trees for comparison:
I think you are rounding the corner!
I’ve heard they get an extra 5 degrees or so of cold hardiness when they get to something like 1” thick trunk or have actual bark. For something like a mature Hass normally rated to 30F, I don’t know if that means it could take 25F. Either way, the bark and thicker trunk definitely give it a hardiness boost.
I’m in Kyoto and saw a 2 year old probably grocery store avocado seedling in a pot on the street. Only had a couple little black branches on it. Curious if they put it inside during winter. Japan is trying to develop a cold hardy avocado they can grow to replace some types of citrus that have become less popular. Kyoto for example usually has a low of 30F during the coldest month January but it did have a dip down to 23. Seems like they could plant Bacon and Zutano and the next years will be less cold than this one… they might be ready to start growing their own
It is not particularly cold hardy, definitely not enough for here, though I did try to graft a scion this spring because I wanted to see if it could fruit in the greenhouse. The graft failed, though.
Since it’s a Guatemalan type (or maybe a complex hybrid), it doesn’t ripen until after winter. Greg Alder’s chart only includes a few true Mexican cultivars, which I’ve circled in purple, but anything below those top 3 on this list are going to take too long to ripen for zone pushing:
I should add that here the ripening time may be later, due to delayed flowering in spring compared to southern CA, so early ripening is definitely on the “traits to select for” list for this project.
Well it looks like we might get our first mild frost in a week! Forecast is currently a low 34°F/1°C next Saturday, and due to local cold air pooling in my neighborhood we’re usually a couple degrees colder than forecast on clear/calm nights.
Most of the outside avocados are in the midst of strong flushes now, so it’ll be interesting to see how this tender young growth handles even a mild frost, in previous years everything was more hardened by the time frost hit. Here’s the own-root clone of Aravaipa, for example:
I was out taking pre-frost photos of everything this afternoon and thought I’d show a comparison between the seedling with the largest leaves (#37, seedling of Mexicola Grande) and the one with the smallest leaves (#311, seedling of a tree in Gainesville, FL that is believed to be “Del Rio”).
First, here’s #311:
I removed the largest leaf from that one and placed it on a leaf of #37 (which is actually curved and is even bigger than this photo makes it look):
That seems to have handled the frost quite well.
Was below freezing for ~6 hours this morning with a low of 30°F (-1.0°C), so I’ll post some photos later this afternoon when I get a chance to walk around and do a survey of damage. I’m expecting that at least some of the trees that were in the middle of a new flush will have slight damage, but also many of the first-year trees are seedlings of varieties I haven’t tested at all yet, so there could be more widespread damage to a few of those.
Just finished my post-frost survey, mostly there’s no damage or only slight damage, but a few are worse than I expected.
It’s no surprise that #149 (seedling of Duke), which was the hardiest new tree last winter, shows no damage from this freeze:
I’m happy to also report that #37 (seedling of Mexicola Grande), the 8 ft tall giant in my front yard, shows no damage even on the branches that hadn’t quite finished hardening a recent flush, like this one:
Both of the first-year “Del Rio” seedlings in the ground (#326 & #335) show no damage even on tender recent leaves:
Among the named varieties outdoors, most show no damage. For example, “Etsicola” aka “Not Mexicola,” originating as scionwood from an Etsy seller, has passed its first test with flying colors:
The Northrop graft that survived last winter is similarly undamaged from this freeze:
Same for the Poncho graft that was undamaged last winter (with some protection for the worst freezes):
These grafts of Opal (left, smaller) and Magdalena (right) show no damage even though they each had an unhardened recent flush:
But not everything fared so well. Oddly, the Aravaipa clone on its own roots shows quite a bit of cellular damage on the leaves, including some even on hardened leaves:
The Ganter graft shows moderate damage on all the semi-hardened leaves:
This Jade graft was in the middle of a strong new flush, and all those tender leaves and stems look crispy, but the hardened leaves look undamaged:
And some of the seedlings outside show quite a bit more damage than expected, including this Mexicola seedling (#145) that regrew very vigorously after last winter, but seems to have very tender leaves, even some that were hardened:
This Duke seedling (#147), which grew back nicely after last winter, was in the middle of a vigorous flush, and all the tender growth looks killed:
I think that’s enough to give an idea of the range of damage, even though there were dozens more outside, including many in pots that’ll be brought into the greenhouse for future freezes now that their initial/minimal hardiness is tested.
I was just taking more photos of the dozens of other potted seedlings and there were two more that really stood out in terms of zero damage on some very tender new growth.
First up is #231, a seedling of “the Granddaughter.” As I understand it, “the Granddaughter” is the first fruiting-age seedling of “the Daughter,” which is a vigorous and productive seedling of the “Gainesville” cultivar. So #231 could be called “the Great-Granddaughter” perhaps! Here’s how it looks after 30°F:
And the other one that is worth mentioning is #311, the same Del Rio seedling with the tiny leaves from the other day. Not even a hint of frost damage:
Very cool! I like seeing you’ve made some initial progress on this. The leaves on #231 look packed with anthocyanins, which might be helping protect against frost.
Have you considered getting a geodesic dome style plant cover to get avocado trees mature enough to endure our PNW winters?
They’re fairly affordable, very study, properly anchored to the earth, and easy to put up & take down. And they give a mildly surrealist vibe to the yard when they are assembled during cold weather and the top of the dome glimmers with ice crystals.
I’ve found they not only work very well as cover for the avocados, but also sensitive citrus cultivars like temple oranges. Clearance is 12 feet at the top, so more than enough room for an avocado or citrus tree pruned to fit.
I like the dome since it can be put up only when the forecast necessitates.Though we’ve also ordered one of the larger sizes, that has a 14 feet diameter. I can get several trees under there.
We’ll be leaving the large one up all winter as an escape from the cold. Put in a couple of lounge chairs, table, fountain, dragonfruit hanging baskets and brugmansia for a splendidly fragrant subtropical retreat mere steps from the back door.
Have you seen this short video of the guy giving a tour of the avocado, loquat and persimmon trees in London?
At this point the goal is to find specimens able to survive unprotected by year 2, or at least year 3, rather than expending energy trying to protect trees that may never prove to be hardy enough anyhow. I think our occasional milder than normal winters will be plenty sufficient to let trees get bigger sometimes.
I’ve got ~30 trees in the ground, it would be a lot of work to protect all those. I may protect one or two of them with grafts I don’t have backups of, but maybe not. So far, nothing has been protected this fall. The ~30 trees that I distributed to project members this spring will have varying levels of protection, so some members may choose to expend more energy than I’m willing to get their trees bigger before properly testing them for hardiness.
I get it, and totally realize a cover clashes with the methodology of most your trial. I’m doing a similar thing here with uncovered citrus and avocados to see what can live without protection.
So far this week we’ve had 3 nights in a row at 28 and not a lick of damage on anything. In fact, the citrus and avocados still look super happy. I see no difference whatsoever from a month ago. My citrus are still actively growing. I don’t know if the avocados are, but they were doing so for sure up until last week, despite several nights close to freezing.
At the same time, for some of the more tender specimens, those that I really want to grow, but know don’t have a chance in this climate (like temple oranges and Gwen avocados), the dome will be a pretty nifty set up over my patio.
The guy who suggested it lives in England, and it gives him the opportunity to grow meyer lemons without struggling. I envision a clean, fragrant, well lighted place, with fuchsias, brugmansia, temple oranges and Buddha’s hand citron growing around a fountain in the center. I think it would be a lovely place to sit and read while listening to rain thrumming loudly overhead.
Send me a direct message to discuss sending you the manzana pepper plant. I also have several basjoo pups from my hardy banana if you’d like one of those too.
I wouldn’t say that. Part of the point of doing this in a decentralized way is that each participant has complete control over the level of protection they give the trees they are given. And I have used buckets and small frost covers for a few of the more promising trees during bad freezes.
But in general, I am already putting so much time into this project that I don’t have the extra time and energy to also protect more than a few of them.
The seeds of “Daughter” are the most eager to sprout so far out of the ~150 seeds I’m starting this winter:
“Daughter” is a mature, productive seedling of the “Gainesville” cultivar, and was also grown in Gainesville. It has been fruiting long enough now that some of its seedlings have also started fruiting in Gainesville, including the one nicknamed “Granddaughter,” which I grafted earlier this fall on 4 seedlings, hoping at least one will make it.
Here’s a breakdown of the seed parents of the seeds I’m starting for next year:
Sorry if it’s been answered prior, but how are you sourcing so many seeds?
