The great Seattle cold-hardy avocado trial

I finally managed to get avocado trees with duke 7 rootstock. After my friends who were going to Spain could not bring me the plants, I finally found a nursery which shipped to Germany (Campo de Benamayor). I would like to cut off the grafted variety (Bacon) in order to graft cold hardier varieties later on although it is a shame as it has a lot of flowering buds. The grafting point is about 5 cm above ground level. Would you cut at this point or just above ground level?

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Can you post photos of the base of the trees? Depending on the diameter, I would probably suggest removing the graft and then wait for new shoots to come up from the roots to graft on those. But maybe you could just graft on the existing trunk.

I’ve generally had better luck grafting on younger wood, though, and I’ve heard similarly from other people like Brad Spaugh, who always stumps his rootstocks and grafts on the new shoots. Here’s a profile of his orchard:

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So there is one first-year seedling in the project that so far stands out as the only tree that was outside without a heat source and still has living leaves! It was next to my house, but the sensor next to it still showed 17°F as the low, and all six other trees huddled in the same location died back much more, including a third-year seedling in the ground that looks like it is dead above ground for the third straight winter. Presenting #301, a seedling of Del Rio from Gainesville, FL:

The other promising new tree is also a seedling of Del Rio, #326, which has the distinction of being the only outside tree that seems to have buds swelling above ground currently:

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So is the breeding plan to find the best seedling of each famous parent and then cross them? In the hopes that they have different cold hardness genes that can be combined

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The first long-term goal is simpler: find at least one specimen that can survive here long term and only suffer superficial damage from our worst freezes, able to fruit at least in a majority of years.

Until we have at least one tree that can do that, I think it’s premature to make plans about what to do with future generations of seedlings.

What I’ve done so far is compare the relative survival and damage rates of seedlings of various allegedly hardy trees, to see which varieties I should be favoring in the limited greenhouse space, to produce seeds on an ongoing basis.

EDIT: I should add that yes, I’ll be keeping at least half a dozen varieties in the greenhouse, once I decide which ones to favor, and will be making intentional crosses among those in the hope their hardiness comes from different gene combinations, which might not have been mixed by anyone else yet.

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Hallo swincher,
Thank you a lot for you quick answer! Here are two photos of the basis (the scale is in centimeters, sorry).


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I am sure there are a few ways you could proceed, but what I would personally do is plant them in the ground in their final locations as soon as your last threat of frost is over.

If you are certain you don’t want the grafted variety, then cut it off just below the graft when you plant it. Allow only 1 new shoot to grow from the rootstock (whatever seems most vigorous at first), rubbing off the others. Once that shoot reaches a graftable thickness (probably middle of summer), then graft on that.

You will need to provide pretty significant protection next winter, as avocado grafts seem a lot more frost tender the first year or two than later. It seems that the callus tissue is extra sensitive to freeze damage even compared to green stems, so protect the graft until it hardens into proper bark.

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Thank you so much for you advise! I will cut off the grafted variety but I’ve planed to keep the trees potted in my unheated greenhouse for two years until they are less frost tender and then plant them in the ground.

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Then I would suggest moving them up to large pots. I use 15 gal when I plan to keep a tree for more than a year, and I think you’d want 20 or 30 gal if you want a happy tree beyond about two years. Part of the reason I suggested planting in the ground is that would give the roots a chance to also grow vigorously.

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After not flowering in the first two seasons after being grafted, the largest Jade graft in the greenhouse has about 25 terminal buds with flower density similar to this one. Hopefully that’s enough to get some fruit this year!

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Hello there from Gig Harbor, WA. I stumbled upon your thread here while in another thread on growing pomegranate’s in PNW. Very intrigued as I too am trying to grow seedlings and grafted avo’s here.
I did start from the start of the thread, but as it’s so long I jumped to this year after around 150 of the first.
I did see mention that you have a website dedicated to your project, can you tell me where to find it? Also, w/o having to go through all the whole thread. Can you mention what cultivars you’ve had the best luck w growing here in greenhouse and if any unprotected outside greenhouse?
Thank you for your time and efforts in trying to grow avo’s here in PNW.

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Welcome to the forum! Here’s the page where you can join the project if you’re interested, and here’s the list of grafted varieties.

At this point there are no varieties that I’d recommend outdoors here, unless you’ll be covering them for our worst freezes. The goal of the project is to plant thousands of seedlings in the hope that some could maybe survive in our climate.

It’s too early to really draw any conclusions yet as to greenhouse varieties, either, as the greenhouse trees didn’t set any fruit last year. Hopefully some fruit will set this year, with about twice as much biomass and a couple varieties flowering that didn’t flower previously. But if not, then there may be issues with the overnight lows during flowering, which can impede pollen tube formation and embryo development.

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Almost 4 weeks later, still no open flowers, but things are coming along nevertheless. Here are all the varieties in-ground in the greenhouse, roughly in order from “most awake” to most dormant…

Joey:

Jade:

Walter Hole:

Duke:

Linh:

Stewart:

Brissago:

Aravaipa (vegetative only?):

Wilma:

Teague:

Forgot to photograph: Long South Gate, which would be between Aravaipa and Wilma, with only vegetative buds so far.

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i skimmed through much of this so i may have missed if you or someone mentioned it, but i read that the most cold hardy avocados have an anise smell to their leaves, i noticed so far that Fantastic, Joey, Lila, Brazos Belle, Poncho and Mexicola Grande have the anise smell.

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Yes, the Mexican botanical group (aka race) generally has a scent that is lacking in the leaves of the Guatemalan and West Indian (aka “Lowland”) botanical groups. The scent also seems to be lost in most hybrids between Mexican and other types, though some Mexican-dominant complex hybrids retain the scent.

However, it’s not universally true. For example, the Del Rio cultivar is one of the hardier ones and it has almost no scent. However, I’d argue that Del Rio looks more like the “wild criollo” type and may not be descended from improved Mexican-type cultivars at all. It was originally discovered growing near the Mexican border in Del Rio, Texas, not very far from the study area for this study, which found some very primitive/unimproved avocados growing in Nuevo Leon, Mexico:

But yes, in general, most members of the Mexican botanical group have that scent pretty strongly.

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Do you know if any hybrids of the Mexican strains exist with the Caribbean or tropical avocado strains?

I know there are many hybrids between the Mexican strains and the Guatemalan and that these do well in California.

But looking for an avocado that is both cold hardy and that ripens in less than seven months from flowering, and may be a bit more salt tolerant, I wondered if any hybrids between the Caribbean and Mexican strains already existed and wether they produce fruit as fast as the Mexican strains do.

Do you know of any? And did they inherit any cold hardiness and early fruiting?

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Lula is often described as such a hybrid, but I think it’s actually WI x Guat., and it may be ever so slightly more cold hardy than other Lowland/WI cultivars, but I don’t think there are any WI/Mex hybrids that are anywhere near being truly cold hardy.

Your best bet if you have soil salinity problems is to purchase clonal rootstocks that are proven to be more salt tolerant, and graft on those. Dusa is fairly salt- and cold-tolerant, for example, but Viveros Brokaw (in Spain) has a bunch of both clonal and seedling rootstocks that they’ve tested pretty extensively in different soil conditions. Here’s the chart from that page, comparing the main clonal options (“D-7” here is Duke7):

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You wouldn’t happen to know what kind of rootstock LaVerne uses?

Nope, but I would guess either Bacon seedlings or Zutano seedlings. Those are the main rootstocks used by CA nurseries that propagate for the retail market. Clonal stuff is mostly sold only directly to commercial growers by places like Brokaw. But I bet if you could find their phone number they would have a quick answer. Most places I’ve called were not at all shy about saying what they use for rootstocks.

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Thanks. I hope not either one because they tend to be large trees. I have a Gem and Pinkerton. They recently sold or merged and I couldn’t get any information from any of them calling. So I went to the nursery (Green Acres) I purchased them from and had the purchasing manager email and call but he couldn’t get any info either, I do know of someone that was able to obtain a few trees from Brokaw. Very lucky.