Beautiful website. This is very fascinating work indeed.
Have you considered minimally protecting your trees with winter frost blankets/Christmas lights?
It seems so hard to grow them even in parts of Northern California that maybe a little bit of “cheating” with microclimate isn’t so bad?
I’ve thought about it, but at least for now I think killing as many seedlings as possible is providing the strongest selection pressure.
I’d rather find that, say, 1% of seedlings (these are made up numbers) that are extremely hardy instead of the, say, 20-30% that can probably do ok with protection most winters.
If, after a few years, it starts looking like the percentage in the extreme hardiness category is closer to 0.0001% or something like that, then I’ll probably switch to protecting them more.
Also, while I’m not protecting the outside trees planted in the ground in my yard, this is the guidance I’m giving to people who join the project and get trees from me:
If you wish to protect the trees while they are young, that is fine, but please let us know the type of protection you have given them in your updates, so that we do not misjudge their hardiness.
A great site - the amount of work that went into providing comprehensive details is evident… and your final comment reflects an honest appreciation!
Last call for anyone who wants a chance to get a tree this coming spring!
Based on the level of registration now, many members will already be getting fewer trees than requested, but we might hit the “more members than available trees” threshold soon, so I’m going to allocate trees to members based on the member list as it stands this coming weekend, and update the sign-up page to warn people they are signing up for 2024.
I will get a mexicola grande avocado soon… it’s great because it’s an A and very cold hardy… 
That’s great! I finally have it grafted myself, though not sure the grafts will take yet. The three seedlings of Mexicola Grande that I’m growing are definitely among the hardiest. No damage even on new/soft leaves at 29°F a couple nights ago.
However, there are actually a few cultivars that have been sold as “Mexicola Grande” over the years. The one most common in southern CA is a synonym for “3-1-1” but it’s also been used to refer to any large-fruited Mexican-type with black skin. Here’s 3-1-1:
http://ucavo.ucr.edu/avocadovarieties/VarietyList/3-1-1.html
The version I have is from someone who bought it years ago from a reputable nursery in southern CA, but I’m not sure if it’s the 3-1-1 version.
My tree will be big and grafted… but not a cultivar… it’s a mexicola grande and i’m very happy!
What I meant is there is no such thing as an official version of “Mexicola Grande,” so there might be many genetically different varieties sold under that name by different nurseries. They may not all be equally hardy, but I’m sure they will all be hardy enough for your location.
Yes that’s what i want, a hardy A variety to plant on side of my bacon that have a very poor pollination…
And i think a very interesting thing that this variety have a thin edible skin… we can eat it like an apple! 
I think most pure Mexican types are like that. I’ve eaten both Mexicola and Aravaipa with the skin on and they taste fine. Bacon is thin enough to eat, so I tried it too, but it tastes bitter.
I never imagine to eat a bacon skin… for me it’s not much thin…
I wonder if there are multiple Bacon varieties, too? This is the Bacon I’ve tried (and source of my Bacon seedlings):
It’s hard to tell how thin it is from the photos, but it was paper thin and soft.
Mine are very small… but like that.
Maybe your climate causes the skin to be thicker than in California? If so, the same thing might happen for the Mex Grande.
This one will kill you… avocado and feijoa jam! 
I posted a twitter thread surveying frost damage after we got down to 25°F last night. Mostly good news, some damage though. Because twitter may face an early demise soon, I unrolled the thread here instead:
And archived here in case that website doesn’t actually store local copies:
After second night in a row around 25°F (this time 12 hours below 30°), I’m amazed to report that grafts of Northrop, Aravaipa, and Poncho still show essentially zero leaf damage, let alone stem damage.
Here’s Northrop (the damaged branch is from the rootstock, which hopefully won’t die this winter if it’s that tender):
This is what Northrop looked like early this morning:
Here’s Poncho:
And Aravaipa:
Here are the last couple nights:
About half the outside seedlings show significant leaf damage, and most of them have at least a tiny bit of damage. This one year-old Aravaipa seedling is among the least damaged:
This Duke seedling is more typical of the first-year seedlings, with older leaves mostly ok but newer leaves turned crispy:
