Haha the magic of a child’s perspective
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Many of the trees have started shedding leaves today. Oddly enough, I usually see this as a good sign. When the entire stem is dead, the leaves usually are held for longer than when the stems are alive and the leaves have been killed. In other words, this type of leaf drop is a physiological stress response that at least implies there’s enough life left in those stems for any kind of physiological response to occur.
Here’s an example of a very dead tree that has not dropped any leaves yet (#153, Duke seedling):
By contrast, here’s the top of #37, the large recently-boxed Mexicola Grande seedling, above:
And here’s #149, a Duke seedling, showing leaves being held near the top (damaged stems cannot trigger leaf drop), being dropped in the middle section (living stems aborting damaged leaves), and held near the base (enough life is left in the leaves for the tree to keep them for now):
Here’s an updated photo of #37 from further back:
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greenhouse here is steady 39F low, one container is low by the ground and the rainbird states it was down to 30F overnight in that low flow area. no frost damage apparent on it at all.
it was negative 4 here outside
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Wow that’s too cold for me! Good job keeping the greenhouse that warm, though. Maintaining +45° is no small feat! Or even +35.
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I’ve been following this thread for a while now and I’m always happy when swincher posts another update.
I live in Switzerland near Lake Constance (northern Switzerland) and my outdoor avocado (Ticino seedling) has just had its coldest night. According to the thermometer -8.9 degrees C / 16°C.
It is only protected by a self-made tent made of PET film. There are also two filled water bottles in the tent. In December it survived a night at -7°C / 18°F almost without damage. I’m curious to see how it survived. I probably won’t be able to look until next week as there is currently a small blanket of snow insulating it too and I don’t want to remove it.
I have other subtropical plants in a tent with padding film (dont know, if this the correct word in English???). This is also unheated. To dampen the temperature, however, there are about 40pcs. 1.5-litre water bottles inside. This has worked incredibly well. Despite several days constantly below 0°C / 32°F (sometimes -6°/21°F), it was never colder than -1°C / 32°F.
Would that be an idea for the next cold snap, Swincher? Water bottles are cheap and are easy to position near the trunk. “Passive heating”
, so to speak. The melting energy of water corresponds approximately to a temperature difference of 80°K. This should not be underestimated. 
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#149 the champion! Don’t want to speak too soon but that tree might have some very famous descendants
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Welcome to the forum, @Marsjaner!
Can you share more information about the “Ticino” seed parent of your tree? This is the first I’ve heard of it. I do have a grafted variety where the ortet is a tree found in Brissago (which I guess is in Ticino?) and I know of an avocado orchard planted near there on the lakeside, but I haven’t heard any of those trees referred to as a “Ticino” avocado.
I have heard of using water as a passive heat source, both as thermal mass and due to the exothermic nature of the freezing process itself, but in my limited testing I didn’t see as much of an effect as you have seen. I concluded that I would need very large jugs to be worth the effort, and I don’t have an easy source of those. But I may experiment with water again, since your results are compelling.
Please continue to post updates here! You are now the third person from Switzerland to visit this thread, so you may find comrades in this endeavor, to share cuttings or seeds with each other. For example, @maesy has not posted in a bit, I wonder how their trees are doing with this cold weather?
It has been impressive for two winters in a row, but as you say it is a little too soon to be sure it’s ok this time around. The roots likely froze near the surface, and it may have a more systemic reaction to that in the coming weeks. I’ve seen trees that seem to survive a bad freeze and hold green leaves for more than a month before suddenly dying. But I’m feeling cautiously optimistic as well.
In case you haven’t clicked through to the profile page previously, here’s the profile for #149, and if you scroll down through the photos you can see the damage last winter from a 3-day freeze with a low of 17°F/-8.3°C. It clearly is more damaged this year despite being a year older with thicker stems, but the freeze was twice as long and a couple degrees colder, so that’s no huge surprise.
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Along a similar vein. I used to modify some home greenhouses in early 2000’s, by adding a thermal mass block. The only greenhouses heater about were parafin ones, which were not good due to the fumes and condensation. Gas and electric were available but expensive to run.
Dig a big hole in the floor of the greenhouse, and I mean big and deep. Then fill it with concrete.
This acts as a thermal store during the high temperatures during the day, and release it during the night. No gas or electric or parrafin used.
General principles to a electric storeage heater are also similar to sand batteries
We used to use domestic electric Storage heaters in the late 1960’s here in the UK. Heat the block up during the night (with cheap rate electricity) then it releases heat during the day. The modern electric Storage heaters do not use very very heavy concrete blocks. Might be worth looking to see what the principles are. I still have some of these heavy concrete blocks in the garden, as all the storage heaters were pulled out when gas central heating came in. They were just to heavy to dump.
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I know maesy - I’ve even met him twice. I am extremely grateful to him. Thanks to him I got Scionwood from Fantastic, Poncho and Joey, which he grafted onto my Mexicola Grande seedlings.
At the moment he’s on vacation, where the climate is much better for avocados than here 
but I’m sure he’ll give an update soon.
After it got very cold again for our region from Saturday to Sunday (-9°C / about 16°F), I opened the tent this morning for the first time since 5 days. This is what the seedling looks like today morning:
To be honest, I have no idea if it will survive. The leaves have very different colors (
), but look more or less fine. I think it’s about 50/50 that the stem will survive. I think the rootstock has survived - Even the big water bottle wasn’t the least bit frozen this morning. A smaller one, however, was half frozen.
I am very convinced of the water bottle method. I think that several smaller bottles give a better result than one large one, as the surface area for heat exchange is larger. I will keep you up to date. Incidentally, the minimum temperature in my other tent (with Air bubble film) with around 30 pcs. water bottles was -3° (despite the outside temperature being -9°). Not a single bottle was frozen.
This seedling itself actually is from Ticino. It was lying on the ground and the flesh was already pretty rotten.It could be a Lila seed, but I don’t know. I just called them Ticino seedling to have a reference
by the way: I found another nice avocado tree in Lugano on the internet:
(Because I can’t share links as a newbie, you’ll have to type the following into Google: “Bellissimo esemplare di Avocado in via Trevano a Lugano Facebook” ) don’t know if it is still alive. But very impressive either way… hope to visit this tree this spring.
Regarding soil for avocado plants in pots: I have had very bad experiences with Avo’s in soil with organic content. When it rained a lot, the soil moulded and I have had root rot. We get about 1,400mm of rain yearly, especially a lot in late summer. All my (many) seedlings always had brown leaf edges after a lot of rain. I repotted all the avocados in mineral soil (Lechuza Pon). It is a mixture of different lava stones - moisture-retaining and at the same time well aerating. I don’t know if this is just nonsense, but I always imagine that avocados thrive in their subtropical region of origin (Mexico) in very nutrient-poor, porous soil (but well-mulched top layer) with not too much rainfall. Accordingly, I hope to get close to these conditions with the Lechuza.
Regarding frost protection: I think it’s not only how low (and long) the temperature drops, but also how high the humidity is. It’s just my theory, but I think that if the avocados are sealed airtight during cold periods (e.g. with plastic film) this should help, as little water sublimates from the leaves, which could dry out the leavse. But perhaps this is also nonsense. What are your experiences regarding this topic?
By the way: I also have a potted avocado Lila (imported from the USA by a friend in 2021), which is now about 1 meter tall. However, it spends the winter in a grow tent in the cellar with an LED-growlight. I haven’t dared to put it inground yet. At the moment there are lots of Flowerbuds. I’ll show pictures in another post.
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Welcome to the forum!
Your plant doesn’t look that bad to me. If there is no visible damage on the stem and the minimum temperature didn’t drop below - 3, I guess it will pull through.
I have two small grafted avocados in ground. One lila and one poncho. I grafted them last summer on fuerte that sprouted in ground the year before. They are realy small and therefore easy to protect with a thick layer of mulch and plastic foil.
All my other grafted avocados are safe in my frost free garage.
Jan, on the pictures of that avocado in Lugano it seems like it’s growing in a pot.
Btw, hello from the Philippines! 
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I live about 20 minutes from the Oroville Duke tree, and have visited it many times. I got lucky and my very first attempt at grafting was with a Duke scion and was successful. Since then I have found it very difficult to graft with, although I’m no pro at grafting.
The Oroville tree hasn’t had fruit in a few years, as best as I can tell. I’ve been to it at least twice a year for the past 3 years. It’s usually ready around November/December.
I bought one of Gary’s Duke trees and I kind of lost touch with which one it is in my yard (still potted), but pretty sure it’s doing well.
One thing I noticed about the Duke is that the skin is very soft, and the seed rattles around inside.
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I’ve had no difficulty grafting it, but have not yet successfully gotten it on its own roots. I do have two more attempts that are still green after almost 2 months, so hopefully those will bud out in spring, indicating roots have formed.
That’s interesting about it not holding fruit. I wonder if someone local is harvesting it with a fruit picker a little earlier than that in the season? Have you tried checking on it in early summer to see what the immature fruit set looks like, or only around the time you’d expect them to be ripe?
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The next generation of seedlings are getting going nicely in the greenhouse this winter, ready to replace their fallen brethren in the frozen battlefield:
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“War is hell” -General Sherman
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I grafted up a bunch of Duke with cuttings from @jsteph00921
So far looks like at least 12/23 are popping through the parafilm. Indoors in an unheated closet with a grow light probably doesn’t get below 40s.
I’m interested in Duke as a replacement for Bacon and Zutano in the SF Bay Area. Most places don’t get below mid ‘20s. Seems like the Duke is higher oil than Bacon and Zutano and also the seeds are probably better rootstock.
One thing I noticed that is interesting is the cold hardy avocados seem to flower 2 months earlier. The Duke budwood had a lot of flower buds and it was collected early January. I also got wood from a Wilma tree that had crazy flower buds Jan 13th
It also seems like the Duke and Wilma are still active during the winter - not growing fast but not dropping leaves either. While all the others are completely stalled.
Overall it seems like growing very cold tolerant avocados in my mild climate is a good way to produce a lot of seeds and budwood for the zone pushers since they seem to have a big growth advantage over the sensitive guatamalans
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My assessment from internet research
Duke VS Bacon/Zutano
Taste: probably better (more oil)
Productivity: unknown
Growth rate: probably better
Seeds as rootstock: equal if not better
Cold hardiness: definitely better
My question: is Duke a Bacon/Zutano replacement?
I’m using Bacon/Zutano together because they are cold hardy to 24F, often used as rootstock, mixed reviews on flavor.
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It’s interesting that Duke was featured so prominently in early UC rootstock breeding, producing the likes of Duke 6 and Duke 7, but even though the latter is propagated clonally, Duke never caught on as a source of seedling rootstocks in the nursery trade, the way Bacon and Zutano did.
I don’t really have an answer, other than to say that Duke has been the most vigorous grafted variety in my greenhouse, and produces very uniform seedlings with good vigor and often with tight leaf node spacing (not too stretchy). But I haven’t tested them too much yet, hopefully I’ll start having fruit this year and a continuous supply of seeds. I think @Marta often uses both Duke and Aravaipa seedlings as rootstocks, so she may have some thoughts on your question. Especially with respect to fruit quality, where she’s got lots of experience.
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I like both Duke and Aravaipa seeds for rootstocks. The difference between them is that Duke doesn’t germinate fast if planted outside in fall, but Aravaipa will start growing. I didn’t use Bacon or Zutano seeds for this purpose, never had access to them. Maybe in a few years…
Duke trees are very vigorous and precocious, but I don’t have one now after moving to the new farm . I need to reestablish one.
Aravaipa is the same, fast growing, vigorous, precocious
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I’ve noticed even in my slightly heated but cool greenhouse, all the Duke seeds germinated in November/December (taproots emerged into soil), but about half of those didn’t sprout a shoot until March. The other half sprouted immediately, but didn’t grow much. By the end of the next summer, the two groups were all the same size.
This winter I’m starting a wider variety of seedlings and I’ve noticed a portion have done that same thing, especially among the “Del Rio” seeds, while all the “Daughter” seedlings (pictured a few posts up) are growing quickly in the same environment.
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In case there’s anyone following this thread who is signed up for this project but hasn’t been getting the emails (I gather they often get marked as spam), make sure you’ve done your RSVP for the spring tree distribution asap, because I’ll be doing the tree allocations at the end of this week.
So far, 29 members have RSVP’d, willing to take up to 120 trees in total (a few people in rural areas are willing to dedicate some acreage to the project). Unfortunately, there are only about 55 trees available to be distributed this time, so some people will already get only one tree while others get two. Nobody will get 10 or 20+ trees this time around.
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