The great Seattle cold-hardy avocado trial begins

I potted up that clone of a Bacon seedling today, had pretty good roots after 8 months:

One thing worth noting is the roots all seem to be coming from the callus on the cut end, not the stem that was buried. So cutting the stems to create more callus might help with root formation.

Here’s what the cutting looked like in August when I cut it and put it in soil:

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Damn! That’s a pretty amazing root structure actually. Impressive.
I may have to give this another go.

A new exciting development! The original seedling that this is a clone of (#89) has survived its first test winter outside! Just noticed it has a new shoot coming up from the roots (the graft of Brazos Belle just above didn’t make it sadly):

It is interesting that this is waking up so early, many of the other seedlings are barely pushing new buds. I may have to reassess where Bacon fits on the hardiness spectrum.

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What a difference a year makes! Just thought I’d post a photo of the greenhouse about a year ago:

And today:

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Here are a few photos of first-year avocado seedlings (some just starting their second year now, some about to soon) that are sprouting from their roots this spring after our cold winter and cold spring. Hopefully we get a couple mild winters so they can bulk up a bit before their next test winter.

A seedling of Royal-Wright, which was grafted with Stewart back in January… rootstock sending up a bunch of shoots, but the scion is starting to swell a bit too:

A seedling of Mexicola:

Seedling of Mexicola Grande:

Seedling of Royal-Wright (suspected x Duke based on phenotype and pollen availability):

This is Joey grafted on a Hass seedling (graft union at ground level)… still seems alive but the dormant buds have hardly even begun to emerge:

Seedling of Purple Nebula:

Seedling of Mexicola Grande:

Seedling of Royal-Wright:

Seedling of Bacon:

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Looks like at least one of the grafts of the “Linh” avocado from @JohannsGarden is a success on one of the multi-graft trees:

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Something I was just thinking about relating to your experiment - I know @steveb4 seems to have had success with Hardy Chicago fig underneath a lot of snow for insulation. I know you guys don’t typically get a lot of snow, but had you considered a step over avocado experiment with protection?

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We typically get at most one or two “snow events” each winter, and the snow is usually melted within a couple days. Once in awhile we get a huge snowstorm that takes more like a week or two to melt.

In the long run, though, this is primarily a breeding project to find truly hardy seedlings, rather than trying to find ways to protect any trees that aren’t fully hardy. In other words, I’m happy to kill lots of trees because that makes room for new seedling crosses that might be hardier. I should have 3 or 4 cultivars big enough to hold fruit in the greenhouse next year, and another dozen or more the year after that, so I’ll have more and more opportunities to try different crosses as the years progress.

That being said, I will also be protecting a few grafted trees outside just to see how little protection they need to survive (at a minimum) or potentially even flower and fruit. I’m not sure how well they would respond to that step over kind of treatment, since once established, avocados don’t generally transplant well or respond well to having their roots disturbed. My plan is to try a few grafted trees with just incandescent string lights, and try covering a few with insulated tarps during freezes, with an incandescent bulb on an extension cord under the tarp.

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It just occurred to me that it’s been awhile since I posted an updated list of my grafted cultivars in this thread. It’s too bad the original post can’t be updated!

These three flowered on multi-graft trees in the greenhouse this winter/spring, but I didn’t attempt hand pollination because they seemed too small to support much fruit, and I wanted them to focus on growing for next year:

  • Duke
  • Aravaipa
  • Royal-Wright

These three cultivars are similar in size on greenhouse multi-grafts, so if they flower next year I’ll hand-pollinate them along with the three above:

  • Brazos Belle
  • Joey
  • Jade

And then come the newer grafts, which might flower next year, but unless they surprise me with their growth this summer, I’ll make them wait another year before letting them try to hold fruit. The italicized ones are on greenhouse multi-grafts, the rest are on seedling rootstocks in pots for now, but I may plant one more multi-graft or add them to existing trees next year:

  • Ganter
  • Linh (shown a few posts up)
  • Long South Gate
  • Mayo
  • 3-1-1 (sometimes sold as “Mexicola Grande”)
  • Northrop
  • Poncho
  • Rincon Valley
  • Stewart
  • Teague
  • Walter Hole

Finally, I just received scionwood from two trees that I haven’t grafted yet:

  • a Redlands, CA tree that’s growing “feral” in a park and believed to be a seedling, though the fruit superficially resembles “Mexicola Grande”
  • a tree near Santa Rosa, CA with fruit that resembles “Fuerte” but is believed to be a seedling tree

I have had a couple other varieties that have already kicked the bucket for various reasons. For example, I recently culled the “Houston criollo” because all three grafts were showing signs of possible laurel wilt or other illness. “Winter Mexican” died outside over the winter. Ditto for the alleged “Poncho” I bought from Fast Growing Trees that did not appear to be a Mexican avocado (no scent to leaves). The new “Poncho” from a grower in Texas has strongly scented leaves, so hopefully it’s the real deal. My only “Mexicola” graft died recently after appearing to take fine but not growing for a year, so I’ll have to add that back at some point. Since it’s widely available I’m in no major rush.

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Finally just grafted a couple of these on Bacon seedlings. The scent of the scionwood when cutting it was milder than either Mexicola or Mexicola Grande, but definitely was a scent present. I’ll compare the leaf morphology if any of them end up taking, but seems unlikely this is Mexicola or Mexicola Grande.

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With our pretty extreme cold in late December (6-day freeze with low of 16°F/-8.5°C), and then our unusual/record cold March-present, I’m kind of amazed at how many of the first-year seedlings survived unprotected and have already begun to grow. Some of them have an inch or two of life above-ground, but none of them had their small stems survive intact.

This one is a seedling of Royal-Wright that seemed to have an unusual amount of stem survive, so I grafted onto that in late January. I’ve also pinched the tip of the new shoot in order to encourage the graft to start growing, but no luck yet:

This seedling of Royal-Wright was the most vigorous of all the seedlings last year, but even though it had a pretty thick trunk, it’s almost dead to the ground, albeit regrowing with vigor again. I cut the dried & dead stem off just before these photos:

These two seedlings of Mexicola Grande faired similarly:


This seedling of Mexicola is one of the only seedlings that’s regrowing from an above-ground bud rather than from the roots:

This seedling of Mexicola Grande was outside in a 15 gallon nursery pot for much of the winter, but when it started sprouting in April, it went into the greenhouse for a month, to get a warmer spring (but is already back outside and starting its second flush of the year):

This is another seedling of Royal-Wright that was in a nursery pot outside (12 gal), but only started sprouting last week, so never got the greenhouse treatment:

This seedling of Bacon was one of the first outdoor seedlings to sprout new growth this year, and has also been successfully cloned by rooting stem cuttings (and looks like a good stool bed candidate):

Finally, a seedling of Royal-Wright that has also been successfully rooted from stem cuttings, just sprouted about two weeks ago but is growing nicely:

There are others sprouting, but those ones are further behind these, so I’ll save them for a future post.

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These two seedlings of Aravaipa were germinated in the fall and overwintered in the greenhouse until March, when they came outside to harden off, experiencing a few mild freezes, with a low of 27°F, when their leaves were damaged somewhat. But, they’ve really taken off in the last couple weeks with a new flush, despite our cool spring:

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A few more outdoor seedlings are starting to wake up. This one is a seedling of “Purple Nebula,” a seed-grown tree in northern CA, and one of only three first-year (starting second year now) trees that regrew above-ground buds this spring:

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The slower-to-start graft of “Linh” (first photo) is now clearly the more vigorous grower of the two, with the other one having stalled out a bit:

The one grafted on Royal-Wright seems to have redder leaves, I wonder if the sap picks up something from that cultivar on the way through that makes the leaves turn red easier?

Those are both on a multi-graft tree in the greenhouse, while the one on a Mexicola seedling in a pot outside is growing more slowly, but seems like a take as well:

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That graft has loved the last couple 100°F+ days (in the greenhouse, that is), here it is just 4 days after that last photo:

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New seedling of Duke, germinated over the winter, has gone into the ground in my planting strip (helper baby makes a cameo):

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The more vigorous of the Linh grafts is still strongly pushing its flush:

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The grafts both failed on that one (one was knocked off by a cat burying its waste), but the rootstock seems like it’s going to regrow fine, so I’ll try grafting it again at some point. Here’s what it looked like today, when it got its first taste of the hose so far in this wetter than normal year:

Seems like Linh may be the most vigorous of any new graft to date:


It’s already caught up and surpassed the growth on a couple grafts from months earlier. At this rate, I wouldn’t be surprised if the graft sets fruit next spring.

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Almost one year later, this tree is now also the most vigorous of the trees that regrew from their roots after being killed to the ground in December. Though it’s almost exactly the same size it was a year ago, and still has a ways to go to catch up with the trunk size when it was frozen to the ground!


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