February 20, 2025 by IG

The Drymifolia Collective: A Quest to Breed a Hardy Avocado

Everyone who joins the Garden Revival community has a story to tell, whether it’s the love of growing vegetables their grandfather instilled in them, the daring dumpster plant rescue or the nursery business they’re committed to getting off the ground. There is something to glean from everyone, whether it’s horticultural knowledge or the depths of human tenacity. Winn joined our community in September, offering free avocado seedlings to anyone in the Pacific Northwest, asking for nothing in return but occasional updates on how the plants are doing, submitted to the Drymifolia Collective website. He was on a mission to breed an avocado hardy enough for his region and boy did I have questions for him.

IG: Can you tell us about the Drymifolia Collective?

Winn: We’re a group of about 100 people (so far!) trying to either locate or breed avocados that are sufficiently adapted to the lowlands of Cascadia to survive here outdoors and at least occasionally bear fruit. The members are concentrated in western Washington state but also there are members in British Columbia and western Oregon, as well as some honorary members outside the area who have helped with seed and cutting collection. I call myself the “lead organizer” and I personally start most of the seeds in my greenhouse in Seattle before distributing first-year, second-year, and third-year trees to project members.

Botanists assign avocado trees to one of three races (some prefer to call them botanical groups) — Mexican (Persea americana, variety drymifolia), West Indian (P. americana, variety americana) and Guatemalan (P. americana, variety guatemalensis.) Our project is focusing on the least-known (and most cold-hardy) botanical group, which originated in the Mexican highlands where avocados were first cultivated by the indigenous people, perhaps 5,000 years ago or more.

IG: How did this idea come to be, was it a sudden epiphany or was it something you thought about for a while?

Winn: At some point near the end of 2019 or early 2020, I came across a blog post by Craig Hepworth titled Cold Hardy Avocados: Guide to Cultivation and Varieties. It occurred to me while reading it that Seattle has similar minimum temperatures to some of the areas in northern Florida where Craig reported success with hardy avocado varieties, even though the climate has some other unique challenges (including longer duration of cold when it does happen).

Soon after that, when the COVID-19 pandemic hit, I decided that trying to grow hardy avocados was going to be my “pandemic project.” At first, I was just growing and planting them in my own yard, but after repeatedly meeting other people who wanted to try them as well, I launched this project and opened it to the public. The first few members were added in fall of 2021 and the first trees were distributed to members starting in 2022.

IG: How many saplings have been distributed to date?

Winn: It’s a little tricky to get an exact number, due to sources of error like duplicate entries in the database or missing trees I haven’t tracked down, but there are over 500 entries in the database, and I’d guess that I’ve distributed about 300 of those to members since the project started. I distributed a small number of trees in 2022, a few dozen in 2023, and then nearly 200 trees last year. I have also planted somewhere on the order of 100 trees in my own yard (more than half of which have perished).

Left: some of the seedlings started last year. Photo taken July 2024 before Winn began distributing them. Right: a row of trees, freshly planted last July at a member’s home.

This winter I’m starting another 80 seeds or so, and have about 40 or 50 trees from prior years that will be distributed to members this coming spring, so I’ve scaled back a little from the excessive number I tried to distribute last year, but I think this is a more reasonable number for me to be able to handle.

IG: What have the results been so far?

Winn: I’ve been less than diligent about making sure I get updates from people who receive trees, especially the earliest distributions where I hadn’t figured out the logistics so well yet.

In my greenhouse, the grafted trees are 12 feet tall and flowered profusely last year, but ended up only holding a single fruit to the end of the season. Unfortunately, it turned out that one fruit is on a hybrid variety that may take 13 months or longer to ripen, so the first fruit in the project still has not ripened yet!

Interior of Winn’s greenhouse.

In my own yard, I’ve got about 40 trees in the ground outside, some of which were planted in 2021, but most of them more recently. They typically die above ground during our worst winter freezes, and then most of those end up re-growing the next season. Although there are still a few of the first trees that I planted in 2021 in my yard, none have survived our worst freezes without injury or protection. However, those earliest trees were from a relatively small number of allegedly hardy varieties, and I’m confident that some of the newer seeds are from even more hardy trees and their seedlings may prove to be hardier than their earlier comrades in the project. Nevertheless, it will likely be many years before this project can start to claim any real progress or results in terms of variety selection or breeding.

IG: Who are the people growing out the avocado saplings?

Winn: Mostly, it’s home gardeners and small-scale farmers, though there was one elementary school science teacher that signed up and one regional community garden organization took a few as well. A few people with small-scale commercial farms have expressed interest in dedicating a few rows of their orchard space to experimental avocado plantings, so that’s also exciting.

IG: You distribute both grafted and own root saplings. What is the reasoning for this approach? Why graft?

Winn: The vast majority of the trees are distributed as ungrafted seedlings, but a few of them are grafted trees, or even rooted clones of other trees. Grafting lets you test two trees at once — the rootstock for root hardiness here and the grafted variety for stem hardiness. If the graft is killed, then usually the rootstock will regrow and it will be treated just like any other seedling in the project.

Most of the named cultivars that are alleged to be cold-hardy are unlikely to be sufficiently hardy for our climate, but most of them also have never really been tested in this climate. Even in this project, most of the grafted varieties have been kept in a greenhouse through the worst of the freezes. Therefore, it’s helpful sometimes to distribute copies of greenhouse varieties to other members, to help guide decisions about which greenhouse grafts are truly the hardiest and which may need to be culled.

IG: When grafting, what variety do you use for the rootstock?

Winn: I’ve mostly used just whatever seedlings I had that were about the right size for whatever scionwood I had. I did use ‘Hass’ seedlings initially but they have proven to almost never regrow in spring, so I think their roots usually aren’t hardy enough for our climate. I’ve ordered a few ‘Zutano’ and ‘Bacon’ seedling rootstocks from Fruitwood Nursery, and those were very healthy and had good success rates for grafting, but ultimately their roots only seemed to survive for fewer than 50% of seedlings. There’s not much point in using an insufficiently hardy rootstock, even if the grafted variety may be hardy enough. For some of the hardier varieties, I’ve seen 90% or better root survival for seedlings, so it makes sense to use those as rootstocks whenever possible.

IG: What have been the biggest challenges in undertaking this project?

Winn: Initially, the biggest challenge was finding reliable places to get the genetic material needed for the project (both cuttings and seeds), because most of the hardy varieties are not grown commercially, and many of them are only available from a few hard-to-obtain sources like the University of California South Coast Research grove (over 100 accessions) or the USDA repository in Miami (over 600 accessions). I have not yet been able to convince the USDA that this project meets their stringent standards for granting requests for budwood, and I had to visit southern California in person to pick up budwood from the UC grove.

However, once I had collected enough budwood and found reliable and trustworthy sources of seeds, the next major challenge has been that I’m definitely better at growing trees than organizing humans. Some members of the project are very diligent about posting updates without any reminder, while many others have never once posted an update or responded to any emails after they received their trees. Spam filters, crowded mailboxes and busy schedules mean that data collection is spotty at best. It doesn’t bother me really, though, because I think spreading the trees around the region is the more important part of the project initially, rather than actually monitoring every piece closely. Hopefully any successes won’t stay secret for too long.

It seems there are more people interested in torturing avocado trees than I would have guessed!

— Winn

IG: Have there been any surprises along the way, good or bad?

Winn: I’ve been surprised at how many people have expressed interest in the project, even though I try to be abundantly clear to everyone that nearly all of these trees will die when we get a 30-year freeze event, and even the ones that don’t die will likely be killed back to ground level year after year and never really have much hope of producing fruit. It seems there are more people interested in torturing avocado trees than I would have guessed!

IG: What is the lifecycle of an avocado tree?

Winn: There’s a huge amount of variation in traits among individual avocado seedlings. For healthy specimens growing in near-ideal conditions, they often begin flowering as soon as 4 years from seed, but sometimes even large, healthy trees will not begin to flower for 20 years or more. The size of the tree seems to dictate the maturation/initiation of flowering more so than the age of the tree, with most trees first flowering when they reach somewhere around 8 to 12 feet tall.

The Mexican botanical group of avocados typically flower near the end of winter or at least some time in spring, and the fruit usually ripen by the start of winter, 5 to 11 months later. The Guatemalan group typically flower a little later in spring and also have much longer fruit maturation times, usually at least 12 months from flowering and sometimes up to 20 months or more. I’m less familiar with the range of maturation times for the West Indian types, but I think they fall in-between the other two ranges.

Each fall, as temperatures begin to cool a bit, the tree “decides” how many flower buds it will produce for the following season, and the dormant buds on the current-season stems begin to develop as flowers in anticipation of bud break. Unfortunately, because flower buds only typically form on current-season growth, that means any freeze damage impacting those stems will likely reduce or eliminate any flowers from forming the next year.

IG: Can you give us some advice on good avocado growing practices?

Winn: Avocados seem to prefer to be planted in the ground, rather than in pots, and will grow much faster and healthier that way. However, I’ve never tried to grow them somewhere with poor soil drainage. In those situations they can be very prone to root rot diseases, so the recommendation is to plant on the top of a mound of soil.

Unfortunately, avocado trees are notorious for their water consumption, causing destructive fights over water resources when they are grown in water-insecure climates. Thankfully, here in Cascadia we do still have ample water supplies so that I do not feel too bad about watering my trees during the dry season, but nothing is guaranteed with all the changes happening to global climate systems. I would generally not recommend that someone grow avocados if they are somewhere facing potential water scarcity, especially if there’s a dry season where irrigation is likely needed for happy trees.

Examples of Mexican type avocados: ‘Mexicola’ (left) and ‘Aravaipa’ (right.)

IG: How do the flavor and texture of Mexican avocados differ from the ‘Hass’ cultivar people are more familiar with?

Winn: The commercial monolith ‘Hass’ is likely a complex hybrid, but is predominantly a member of the Guatemalan group, which have a medium to large sized fruit with thick, bumpy skin and a good oil content. Other avocados with small commercial followings in California or Hawaii are also usually predominantly Guatemalan type, such as ‘Sharwil’, ‘Reed’ and ‘GEM’.

You may have also seen the large green avocados sometimes marketed as Florida avocados, which belong to the West Indian group, and they will also sometimes be grown commercially in the Dominican Republic or other Caribbean islands for export. They are typically more watery, with lower oil content and sometimes have flavors ranging from walnut-y to pumpkin-y that can be off-putting to some people.

As a result of being grown in situ in the area where avocados originally grew wild, the more cold hardy Mexican type, which we focus on, is much more genetically diverse than the other two types. Unfortunately, that means that the fruit (and other traits) of this type are also highly variable, so it’s difficult to make too many broad generalizations.

Mexican types typically have very thin skin (similar to that of a ripe European pear), high oil content, and some are very delicious with nutty flavors and buttery consistency. However, due to the high amount of genetic variability, some cultivars or selections have large seeds, unpleasant fibers in the flesh, seed coats that adhere to the flesh, or they may have grassy, licorice, or pine aftertastes that some find undesirable.

‘Mexicola’ cut open.

‘Del Rio’ in a bad year (over-productive tree that was not thinned), though even in a good year they have a lousy flesh-to-seed ratio.

Fruit from an unnamed seed-grown tree that Winn has nicknamed ‘San Josuerte.’ It was mislabeled and sold as ‘Fuerte’ from a tree in San Jose.

IG: Do you have any favorite recipes with avocados or do you just eat them whole, skin and all? I’ve seen the photos.

Winn: Unfortunately, I don’t get to eat fruit of the Mexican type as often as I would like, so mostly I eat the same ‘Hass’ avocados as everyone else. I would not recommend eating the skin of a ‘Hass’ avocado! With the Mexican types, the skin is usually edible, though the unpleasant aftertaste of some cultivars is concentrated in the skins, so it’s one of those “your mileage may vary” situations, where removing the skin may be preferable in some cases even when it could be eaten.

I’m fairly boring when it comes to avocado recipes. Guacamole — incidentally from the Nahuatl word ahuacamolli (avocado sauce) — is always a good choice, as is avocado toast (yes, I’m a Millennial) or sometimes it’s nice to just eat slices of avocado sprinkled with salt and lime juice. For those who eat pork or other bacon alternatives, adding avocado to a BLT is never a bad move.

One bit of culinary advice for anyone growing the Mexican type of avocado is to try using the leaves as an herb, which has a long Indigenous history and is still common practice in Mexico today. Only do this if the leaves have a strong anise scent when crushed, which is a defining characteristic of the Mexican type. For example, the leaves make a lovely addition to beans when lightly toasted and then ground to a powder in a mortar & pestle, but that is not the only way they are used traditionally.

IG: Any final thoughts?

Winn: For anyone wanting to find out more about the project, the website is drymifolia.org, which includes photos of most of the trees in the project, contact information, and real-time temperature charts for the “headquarters” of the project here in my yard.