The great Seattle cold-hardy avocado trial begins

This seems pretty interesting. I have been thinking of doing this with citrus, but am interested in avocado too. How did you get so many seeds of rare varieties?

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Most of the seeds were from members of this forum and the Tropical Fruit Forum, as well as seed donations from supporters of the project on twitter. Most of my grafted varieties were scions obtained from the UC Riverside collections, with a few trees or scions purchased from commercial nurseries or forum members. The “Linh” variety scions were from @JohannsGarden, who has been evaluating its seedlings for release in their nursery.

However, I think you need at least a polytunnel and maybe a heated greenhouse to expect success with avocados in most zone 7b climates.

Yeah I have a greenhouse but I’d be interested in trying to find that one off seedling that can take the cold. I may try and induce some epigenetic changes by inducing a chilling period before germination. Put the seeds in the fridge and then slowly move them to the freezer for increasing amounts of time. Then plant them outside in the winter. I believe you are doing something similar correct?

Yes, but I’m expecting most of the hundreds of seedlings I’m growing to die even in zone 8b here in Seattle, I doubt any avocado can be expected to survive the teens (°F) on a regular basis, let alone single digits. Seattle hasn’t dropped below 10°F in like 40+ years, and I’m hoping it won’t again, since that would likely be killing temperatures for any of my trees that I don’t protect.

But, who knows what’s possible! Where are you located? Zone 7b can be very different from region to region, even though I can’t think of any of them where I’d expect even the hardiest avocados to make it.

I’m on the east coast of NC, it’s a weird 7b. If it wasn’t for the few days of 0 F weather we get every year it would probably not go below 10 F. It’s like all or nothing here. We will be 70 F one day then a low of 0 F the next

This graft continues to impress considering it was one of the last things grafted this spring. It’s this entire small branch now, and is pushing another new flush:

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I can now say with pretty high confidence that “Linh” is not “Walter Hole” – the leaves and stems on new growth are noticeably different in coloration. Linh emerges red and fades to green, while Walter Hole emerges pinkish green.

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How about this difference in coloration and growth habit between a Duke seedling (suspected Duke x Duke) and an Aravaipa seedling (suspected Aravaipa x Mexicola), both in their first year since germination, and both planted out around the same time (~2 months ago) into full sun:

The Aravaipa seedling is nearly 4x taller but they have about the same number of leaf nodes (~30). I’ve noticed that Duke seedlings are generally more squat than most of the other seedlings in my collection, while Aravaipa and Royal-Wright tend to be the tallest.

One of these days I’m going to post a recap of what actually survived the winter, as many of the trees that scratched green in early spring ended up never waking up or sprouting weak shoots that died. However there are also a good number that regrew vigorously, thankfully.

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Decided to finally do a recap of the death count/survivor count for the outside trees from the first winter, with links to either their profiles in this thread or on twitter (if they weren’t posted here specifically). Here goes:

The Deceased

The interesting thing about #53 is that it seemed to survive just fine (even had some leaves that remained green until spring), but then it turned brown and shriveled right when I would have expected it to wake up. I do still have a graft of this seedling on a greenhouse tree, so it’s not TRULY deceased, but the ortet is.

With #100, there were a few small buds that started growing in the spring, but they stalled and then wilted.

No. 107 never woke up this spring, even though it scratched green at ground level for a couple months.

There were also a few that I planted out later that weren’t featured in that earlier post in this thread, such as this grafted “Joey” tree on “Hass” seedling rootstock:

For that tree, the grafted variety seemed to survive the winter fine, but it died when the rootstock failed to wake up in spring. So, that’s a pretty strong sign that cold-hardy rootstocks are maybe necessary, or at least very beneficial.

For this Bacon seedling grafted with Duke, the graft was killed in the hard frost, and the rootstock never woke up even though it did scratch green for most of spring:

Winter Mexican on Lula seedling rootstock, both grafted variety and rootstock appeared dead after the frost (failed scratch test):

This seedling of Royal-Wright, grafted with a criollo from Houston, died in the frost (failed the scratch test on rootstock and graft):

These eBay- and Etsy-sourced seeds seemed shady and did not produce anise-scented seedlings, so were probably just Hass seeds (and all died):

Barely Alive

Number 96 has had a little sickly sprout on the side of its trunk since early spring, but it seems like there’s a local slug that keeps eating it. I don’t expect it to survive this coming winter, but here it is today:

This one is doing better than #96, but #99 is definitely not as happy this year as last year. It could manage to pull through, but doesn’t look promising. This seedling was also one of the first to suffer frost damage on its leaves in the fall, so I am a little surprised it didn’t die completely in that extended deep freeze in December. Today:

Doing Fine After Their Frosty Haircut

I debated putting #23 in the “barely alive” category because it is definitely still kind of sickly looking. However, this is how it has looked since I planted it out in January of 2021 in what I had assumed was an act of euthanasia for the sickliest seedling I was growing indoors at that time. The fact that it has now survived one and a half winters and keeps coming back makes me assume that it will do the same this winter. Wish you luck, little guy:

Number 25 is doing about the same as it was a year ago, and seems to be growing happily:

Number 51 is slightly ahead of last year’s growth, and might be the only in-ground tree that can claim that right now. Perhaps the close proximity to a concrete wall (out of the frame to the left) helps it out a bit:

Last year’s king of vigor, #84 is once again large and healthy, at just about exactly the same size now as early September of last year, despite being killed to the roots in December:

Number 91 is a little behind last year’s growth, though that’s possibly because I allowed it to grow two shoots instead of one this year. It did lose the Royal-Wright graft, though:

No. 102

I’m not sure why I never included #102 (a seedling of Royal-Wright) in my posts in this thread, since it was planted out about a year ago, but it’s another happy survivor, doing very well even though I tried to graft a scion onto it this spring and had been pinching its growing tips to encourage the graft to take (it failed):

No. 89

One of the huge unexpected surprises from the winter was No. 89, a Bacon seedling that I didn’t plant out until early December – only three weeks before the extreme cold snap that killed so many trees. This one not only survived, but was the first to wake up in spring out of all the trees that survived, and is growing vigorously and happily today:

I also have a rooted cutting of this tree, which was one of my first successful attempts to root an avocado cutting. I have visions of something like a stool bed to propagate this cultivar, since it seems prone to sending up multiple shoots any time it is damaged, and those shoots will likely root relatively easily.

Potted Survivors

There is a final category worth noting – potted trees that survived outside. This number is small, but non-zero, which is itself a surprise since potted trees generally suffer more from cold weather than in-ground trees.

No. 82

First, this seedling of Royal-Wright, which has been outside for the entire winter, without any greenhouse stint:



Obviously it’s still a little behind last year’s growth, but still seems healthy enough otherwise. This winter I’ll let it stay in the greenhouse before going in the ground next year.

No. 37

This Mexicola Grande seedling has been very impressive this year, greatly outgrowing the size it was before the top was killed back, despite growing two trunks this time:



The one caveat is I did move this one into the greenhouse after I saw it had buds waking up mid March, but then back outside in late April. So that ~6 weeks of warmer temperatures in spring definitely gave it a headstart this year.

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135 is doing well in the ground since planting this spring. It got topped by a deer early summer but has recovered well.


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I had no idea deer were interested in avocado leaves, that’s good to know. Looks like it’s recovering well from the attack, at least. Thanks for the update!

I was also surprised to see that. I believe it took that bite by mistake. There were a couple of potted mulberries that were standing right next to it that got grazed and this seedling as well (probably inadvertently) . Since moving the potted plants there has been no deer damage.

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The dormant buds on one of the two Duke grafts in the greenhouse look like they might be flower buds, though it’s hard to tell at this stage:

The other Duke graft is pushing another vegetative flush instead:

Not sure what would explain the difference, though they are on different seedling rootstocks with different varieties as a framework, so maybe that influences flush cycles somewhat.

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Two out of the three “Del Rio” grafts I did 3 weeks ago are already starting to push new growth.


This variety was obtained from Craig Hepworth, and he says it has done very well in north Florida. As far as I can tell it’s not generally available in the nursery trade (though some claim it’s the same as “Fantastic,” but I haven’t grown Fantastic yet, so I can’t say). Here’s how Craig described getting “Del Rio” in the blog post linked in the very first post in this thread:

My friend Oliver Moore and I may have been the first to grow this variety in Florida. In 1998, we got scion wood of this one from nurseryman Bill Schneider in Texas, who has a nursery, Devine Avocados, specializing in cold-hardy avocado varieties. Bill had collected this variety from the original tree in the town of Del Rio, Texas. At that time, Bill labelled the variety ‘Del Rio Big’ – in which the word ‘Big’ refers to the size of the original tree (which apparently was huge), not the size of the fruits.

I’m glad to finally have this one in the collection!

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Wow. Very exciting. I got my ‘Shambala’ loquat as it was Craig’s recommendation.

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Next ten Aravaipa seeds, reporting for germination duty!

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One interesting observation this year is how many outdoor avocado trees are still pushing new vegetative flushes here in early October. It’s been unusually warm and sunny (for Seattle), but we’ve still had many nights in the low 50s°F and a few nights in the 40s over the last couple weeks:

And yet almost half the outdoor seedlings are currently like these:










And it’s not just the seedlings, some of the grafts outside are also pushing flushes still, like this “Linh” on a Mexicola seedling, which has been growing less vigorously than its counterpart in the greenhouse, but looks ready to push not only one bud, but its first branches, too:

That one will be staying outside until/unless we get a really bad hard freeze, when it’ll be allowed a brief greenhouse visit this first winter.

A slight majority of the outdoor trees have apparently slipped into dormancy already, which in the end may prove to be the hardier choice if we get an early frost in the next few weeks.

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A little over a month later and this Duke seedling has really bushed out, still showing no sign of slowing down for the fall yet:

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