The great Seattle cold-hardy avocado trial

swincher · February 11, 2021, 8:43pm

If you’re just going to have them in a greenhouse then you’ll probably be hand-pollinating and flowering type won’t matter as much as long as you brush the flowers a couple times each day to collect pollen and pollinate. Also, flowering times vary a lot based on temperature, so it’s possible Brogdon won’t behave like Type B in your greenhouse.

I’d offer scions, but the only cultivar that I have with any extra branches at the moment is Brazos Belle, also Type B.

I don’t know about flowering type for Marta’s varieties, though.

cdamarjian · February 11, 2021, 9:03pm

Thanks for pollination details re: greenhouse. Will be quite a mystery to explore!
Another question: If I am hand pollinating, would I still need another variety (either A or B) or could I hand pollinate a single Brogdon plant, saving pollen from morning to evening?

I contacted Marta. She has scions of Duke, Aravaipa, and Royal-Wright but wasn’t sure about their A or B status. She said she would check once they bloom in spring.
Thanks, Chris

swincher · February 11, 2021, 9:10pm

From the research I’ve read, most avocados are self-fertile other than the flowers shedding pollen at a different time of day than they are receptive to pollen. And depending on temperatures, there can be a significant overlap.

I did read one study (don’t have it handy or I’d link) where they did genetic analysis of seedlings and found that many self-pollinated (Hass x Hass) seedlings died mysteriously shortly after germinating, and none of the crossed (Hass x Bacon) seedlings had this issue. But it was a relatively low percentage in any case.

There are also some reports of lower levels of premature fruit drop when cross-pollinated vs self-pollinated, but many commercial orchards are single-cultivar, without pollenizers, so clearly that’s not a major factor either.

cdamarjian · February 11, 2021, 9:16pm

Thanks. A lifetime of learning.
Then I’ll go with some scions from Marta and see what happens!

disc4tw · February 11, 2021, 10:42pm

This might not be the BEST place to put this, but I can’t help myself. Avocado, baby by Los Campesinos!

swincher · February 12, 2021, 4:24am

Here’s the study I referenced above, and they found that 24% of the Bacon x Bacon seedlings had a lethal mutation, 46% of the Hass x Hass seedlings had a different lethal mutation, and none of the Hass x Bacon or Bacon x Hass seedlings had either mutation.

So even though avocados are self-fertile, it does look like there’s a good reason to cross-pollinate if you intend to plant the seeds.

[23279834 - HortScience] Outcrossing between ‘Bacon’ Pollinizers and Adjacent ‘Hass’ Avocado Trees and the Description of Two New Lethal Mutants.pdf (1.4 MB)

cdamarjian · February 12, 2021, 2:51pm

Thanks. Similar to marriages of familial nobility, recessive genetic traits emerge in offspring. Makes me wonder about saving the seeds from any plant that self pollinates, e.g tomatoes! Hybrid vigor must be good.

swincher · February 16, 2021, 6:42am

I’ve decided to do a post that sums up some of the useful avocado-specific documents/websites that I’ve been reading lately, in case anyone else wants to read up on this stuff.

First, Propagating Avocados (1989), a publication of the University of California that summarizes grafting and seedling sprouting techniques used by commercial nurseries and avocado growers in California.

Next up, the web-published guide from the Western Australia department of agriculture, Challenges growing Hass avocado in cool regions. I have no intention of growing Hass, but much of the research summarized there is more broadly applicable to avocados in cool climates, including how colder temperatures impact type A and B avocados differently.

Then more generally, I have to plug AvocadoSource.com, where I’ve found countless obscure documents and studies with interesting results, including:

Importance of Leaf Retention to Rooting of Avocado Cuttings (more leaves are good, and drymifolia specimens root at much higher rates than guatemalensis or americana)
The California Cross Pollination Experiment – A
progress report on the influence of pollinizer
variety and proximity on ‘hass’ yield (pollinizers can impact fruit shape, seed ratio, seed size)
Avocado Rootstock-Scion Studies (summarizing early attempts to test graft compatibility of avocado with other laurels/Persea species)
Evaluation of Cold-Hardy Avocados in Florida (summarizing experiments at the University of Florida in the 1960s with drymifolia cultivars surviving multiple lows at or below 20°F)
Avocado Production in California: A Cultural Handbook for Growers (lots of good background and info, some very California-specific, but mostly generally applicable)
Rooting Avocado Cuttings (summarizing an experiment that found drymifolia race avocados root more easily than other types, and rooting hormones don’t impact success rates)

swincher · February 26, 2021, 11:01pm

Here’s more of an update on the avocados I’m currently growing. A family photo album of sorts?

Grafted varieties

First off, some success stories from my first attempts at grafting avocados.

Joey on grocery store Hass seedling rootstock (pushing a flower bud, but looks like it’s taking):

Aravaipa on the Choquette frankentree:

Royal-Wright, also on the Choquette frankentree (and also pushing a flower bud but appears to be taking):

Sadly, it appears that Lila, Fantastic, and the other Joey graft all failed, and Brogdon is likely failing as well though it still looks somewhat green.

As a new addition, I grafted three scions of Duke this week, one onto the Choquette frankentree, one onto the Brazos Belle frankentree, and one onto some Hass seedling rootstock that I planted out in the yard just for kicks. I’ve never seen an avocado with such a yellowish looking color to its stems, but that is what I’ve heard about Duke so I will assume they are healthy scions. Here’s the one in the yard:

I have four main “frankentrees,” each frameworked on an already-grafted variety that I bought at 5-gal nursery pot size last year, all on Lula rootstock, and currently in 12-15 gal pots indoors. These are the grafted varieties that are forming the framework for the frankentrees:

Choquette (not hardy)
Winter Mexican (not very hardy)
Poncho (hardy)
Brazos Belle (hardy)

The latter two I intend to eventually plant out, but only when they outgrow my greenhouse. I’m hoping to keep the Choquette and Winter Mexican trees pruned to fit in the greenhouse, and will be continually adding and removing varieties depending on what does better outside. Here are the Poncho and Brazos Belle trees (didn’t take photos of the other two, which are ugly now with lots of grafts on them anyhow):

Seedlings

I’ve got quite a few batches of seeds currently germinating, either to test for hardiness themselves (Mexicola, Mexicola Grande, Bacon, Royal-Wright, alleged Fantastic and Del Rio from Etsy), or for greenhouse/rootstock use only (Sharwil).

The germination technique that I’ve settled on is based loosely on the one described in the pamphlet Propagating Avocados, where the seeds are placed in moist native soil in tight rows and observed for germination, after which they are transferred into nursery pots. Instead, I use take-out containers with damp soil on heating pads:

Then, as the taproot emerges, I move them into their own pots. Here are some freshly potted up:

Most of the seedlings are still inside under lights, like this Mexicola Grande:

And here I’ll finish with a photo of the strangest little seedling of them all – a Mexicola seedling that had the smallest seed I’ve seen yet, and is now producing a tree with the smallest leaves I’ve ever seen for an avocado:

It is currently not in great soil (too much native soil in the mix), so hopefully it holds out nicely until I can re-pot it in the greenhouse in a month or so. So far at least, no real signs of any problems other than its small size and very small leaves.

OK, that’s all folks! Hopefully my next update can be when the greenhouse is built and the plants start moving in.

swincher · March 14, 2021, 1:43am

Decided to plant out the less vigorous Mexicola seedling, which had already been in a shady corner of the patio full-time (about 5 nights below freezing in two weeks, one 27.7° and the rest 29-31°)… and now I know why it was less vigorous!

Looks like the seed split in half when I planted it, so it’s been getting only half the seed energy it should have. Interestingly enough, the other half has now germinated, so I planted it back in a 1 gal pot to come under the lights with the other recently germinated seeds:

Speaking of trees under the lights, the grafts of Aravaipa and Royal-Wright are starting to push out their new leaves nicely:

Greenhouse construction starts in 2 days, I’m looking forward to introducing the avocados to their new home. So I’ll close with the Mexicola seedling out in the yard, future greenhouse making a cameo in the background:

swincher · March 17, 2021, 1:00am

Just got my latest batch of seeds from someone on another forum, which is an unnamed seedling-grown drymifolia variety the grower described as “the oiliest avocado [he’d] ever tasted,” almost like “avo cream cheese.” Here’s a photo that he sent of the fruit:

I cleaned off/peeled all the seeds and threw out one that looked like a fungus had taken hold, planted one that was already germinating, and here are the remaining 8:

One interesting feature, 3 out of 9 (didn’t check the infected one) have something I’ve never seen before with avo seeds, where instead of being in two sections, the seeds are divided into 3 roughly equal ones:

It’ll be interesting to see if these grow any differently as a result.

Onto the heating pad they go:

spurious · March 17, 2021, 3:02am

Since you’re an avo murderer, I thought you might know about the “forensics”. I hope to not join you in murder by the way.

I noticed on a recently purchased tree from a nursery leaves exhibit splotchiness or a mosaic pattern. Subtle but there in most leaves… normal? Virus?

Sun behind the leaves in the photo bring it out, otherwise leaves are deep green and hard to see the described symptom.

swincher · March 17, 2021, 3:19am

Believe it or not I’m pretty new to avocado growing, so not sure what that leaf shows. It could be something as simple as a touch of sunburn, I have never heard of viral problems like that though.

The oldest leaves usually get kind of discolored and splotchy for a few weeks before they are dropped, so it could maybe be the start of that, though usually that doesn’t happen until a new vegetative flush is pushing.

jfiorini · March 17, 2021, 8:06pm

I see you’re in Seattle. I am down in Tacoma, and I REALLY want to plant an avocado, but everyone calls me crazy.

What variety do you think I should get, I was thinking Mexicola or Lila.

swincher · March 17, 2021, 8:30pm

They probably are correct, and I’d say any commercially available grafted tree will probably be on rootstock that’s even more unlikely to survive here than the grafted variety. But the purpose of my testing is to see if it’s really such a crazy idea.

If you’ve got a good protected spot (mostly sunny, against the south side of a heated building, well-drained soil), and are ok with a likelihood of failure, then I would say go with the hardiest variety you can get your hands on, Lila/Del Rio/Wilma/Poncho/May are allegedly more hardy than Mexicola/Mexicola Grande.

If you want to really gamble a bit and can wait a year, I’ll probably have more hardy seedlings to plant out next spring than places to plant them if all goes as planned. If so, I’d be happy to share one or two. I’d suggest growing the seedlings for at least a year to test winter hardiness before grafting anything else on it.

Chonas · March 17, 2021, 8:33pm

How hardy would you expect them to get? 32F death, 20F death, etc? I have lows to 12, so I doubt I’d ever be a candidate in 7b, but I’d love it if I could!

swincher · March 17, 2021, 8:43pm

Yeah, you’d need a cold frame there I think. Once established and mature size, the hardiest varieties can allegedly withstand lower 20s without damage and survive mid-10s with significant damage, but probably not if the ground freezes solid.

I have not tested those claims yet, but the tiny Mexicola seedling that I planted a few days ago appears to have suffered only slight damage after being out in a pot on my patio for lows of 28, 29, 30 spread out over a two week period, and in the ground for 27 and 28 on consecutive nights. So that bodes well if a tiny tender seedling can survive that relatively unscathed.

swincher · April 3, 2021, 7:42am

My greenhouse is running behind schedule, so I thought I’d do a “baby photos” update as the last one before the big move.

I’ve got quite a few seedlings germinating, which will be among the first trees I will plant out that could have any real hope of survival (in about a year). These are all from seeds that I got from other growers, and have unknown pollen parents (though likely many are self-pollinated). Therefore, their hardiness will be even less certain than the crosses I’ll be making myself over the coming years.

If none of this first round make it I’ll keep working on the greenhouse frankentrees and start crossing the various varieties more intentionally.

First off, some of the oldest seedlings, these of Mexicola Grande:

You may notice they don’t look so great, but they are both just starting a new vegetative flush. Their sickly demeanor is a result of spending 4 weeks on the patio in winter to test hardiness at this size. Over that period, they experienced five nights below freezing, including consecutive nights of 28 and 29°F. I brought them in 2 weeks ago to avoid a 27° night, and decided to let them stay under the lights as a reward for surviving that ordeal. I left one outside in its pot, and it’s still alive but suffering a lot (no photo this time around).

Next up, the newest additions, three of the seeds I had just started germinating in my last update (“Purple Cream Cheese”) that already had taproots emerging yesterday, very rapidly compared to most other avocado seeds I’ve germinated:

Here’s a couple Bacon seedlings that spent those same 4 weeks of winter outside, but much earlier in their development (one immediately upon germination, the other 2 weeks further along):

Finally, a few of the Royal-Wright seeds that are just beginning to sprout, including the last one that was having trouble splitting its seed, so I just gave it a little help with the grafting knife:

And as a teaser for next time, a photo of the still unfinished greenhouse (getting close!)

disc4tw · April 3, 2021, 11:18am

Looking good! I have “space for a greenhouse envy ” I have to make do with a grow light and a tiny room below my basement steps like Harry Potter right now haha.

How long will it take to get fruit on the frankentree? I have 2 seedlings in the HP room from grocery store seeds and I’m not sure I’ll ever get them to fruit in Pennsylvania, even under the light inside all winter.

swincher · April 3, 2021, 4:56pm

Out of my 4 larger grafted trees destined for the greenhouse, I’m expecting two of them to start flowering within the next year, since those are already a couple years old and I’ve only added a couple small grafts on each one (I won’t allow those new grafts to set fruit that soon, even if they try). So, hopefully I’ll get Brazos Belle and Poncho to flower in about a year, with first fruit the next winter.

The two most heavily grafted trees are almost entirely new scions, so probably at least two years until I’ll let those set any fruit.

As for your seedlings, my vote would be to graft something onto them for a better chance of fruit, but as long as you’re letting them out from spring to fall, they might still bear fruit eventually on their own. My understanding from the literature (not personal experience yet) is that most seedlings start to flower when they reach around 8-12’ in height, with poor fruit set and fruit quality for their first few years. How long it takes to get that size in those growing conditions is the real question. They also usually flower after cold (though there’s wide variation among varieties on flowering time), so you may want to move them out slowly early in the spring to let them get a bit more cold in the hope of triggering earlier flowering.