The great Seattle cold-hardy avocado trial

swincher · May 24, 2021, 2:34am

This is a little off-topic, but I just wanted to take a moment to appreciate the incredible genetic diversity of the avocado. For example, all of the following photos are all seedlings of @Marta’s Royal-Wright variety.

These seedlings include a number of leaf shapes:

Stem coloration ranges from bright pink to different shades of green with red or purple flecks:

Some leaves have ruffled edges while others are straight:

And those all share the same seed parent! Some seeds from other cold hardy varieties that I’m growing have leaves that are almost round, or others have long slender ones that look almost like mangos:

Even if all this genetic diversity isn’t enough to find Seattle-level hardiness, it’s still something to behold.

swincher · June 2, 2021, 12:01am

Just thought I’d share some photos of an interesting genetic trait in one of @Marta’s Royal-Wright seedlings, where branching occurs in Y shape nodes with a single deformed leaf that forms simultaneously to the two growing tips:

You can also see the stems have a thin depression down the center just below the branching node, almost as if it is already two branches that are conjoined.

swincher · June 5, 2021, 4:43am

I spoke too soon! Coming back nicely from the roots.

swincher · June 16, 2021, 5:58am

After reassessing how many 3 to 5 gallon pots I’d need to pot up all the avocado seedings from their 1 gallon seed-starting pots, I decided to go ahead and plant out some more over the next few weeks. Here are about 2/3 of the 1 gal pots:

I started by planting the largest and most vigorous seedling of Royal-Wright (No. 84, first photo below) and Purple Nebula (No. 96, second photo):

They join two seedlings of Mexicola Grande and one of Mexicola that have been in the ground since February, all of which have started pushing new growth recently. I’ll probably plant out at least 3 more seedlings over the next few days, and then pot up the rest to 3 or 5 gal pots as needed over the summer.

And speaking of the larger seedlings, including a few recently grafted with known varieties, these 3 and 5 gal plants will all be in the greenhouse next winter, but for this summer and fall they will get half-day sun by the north fence in my back yard:

Next up, I wanted to share the beautiful foliage on Poncho/Pancho, in its 15 gal pot in the greenhouse:

It opened about 5 flowers when it had that flush of growth, but as expected none set fruit.

And finally, some Bacon and Sharwil seedlings I’ve just grafted with small scions of Brazos Belle, Aravaipa and Poncho:

swincher · June 28, 2021, 8:51pm

Damn, now this one was the first victim of the heat wave, it just melted this afternoon. I’m trying emergency water resuscitation but time will tell. Poor little plant survives root rot and multiple hard frosts, but it’s the record breaking heat that does it in? In Seattle? Who would’ve guessed?!

Some other seedlings that were planted out seem to be loving the heat. These are two phenotypes of Royal-Wright seedlings:

I guess it’s no surprise that seedlings of a plant known to flourish in the CA Central Valley can handle mere 100ish° without issue.

swincher · June 29, 2021, 2:26am

Once again spoke too soon… it was just thirsty, even though I had deeply watered 3 days ago. This seedling must have 9 lives, though, it’s perked back up (though the leaves look much yellower than they did 2 days ago):

ramv · June 29, 2021, 2:54am

My seedling avocados are nearly dead after this heat wave. This is too hot for most plant types except maybe figs.

swincher · June 29, 2021, 3:13am

I’m sorry to hear that! Mine all seem to have done ok, but I’m in West Seattle where it was a few degrees cooler than the official/Sea-Tac temperature, because of proximity to the sound.

These are all in direct sun in my yard and seem fine (last one has older leaves with frost damage from late winter):

And the rest of my potted trees were hiding under my CA bay laurel tree where they just got morning sun.

They all seem happy enough. Let me know if you’re interested in replacing your dead/dying ones, I have more trees than yard space! I’m counting on lots of in-ground trees dying next winter to make room for the ones spending the winter in the greenhouse.

swincher · July 2, 2021, 5:55am

Planted out another couple trees today, here’s one of the Purple Nebula seedlings in my tinderbox meadow of an unmowed front lawn:

The most vigorous seedlings so far are from the seeds of @Marta’s Royal-Wright tree, and I’m happy to see that the Royal-Wright grafts on both greenhouse trees are pushing new growth. Here’s one of them, with Duke in the background for a little color contrast:

To give an idea of the level of vigor I’m talking about, this Royal-Wright seedling first emerged from its seed on March 4th:

swincher · July 6, 2021, 11:12pm

8 more seeds of Mexicola went in their germination pots today:

These seeds were noticeably smaller than the Mexicola seeds I got last time from a different source, both of which seemed reliable. So that makes me wonder whether all “Mexicola” trees are really the same variety or whether that term has been used generically for any small, black Mexican subspecies avocados, including seedling trees from different lineages with similar fruit. I guess there’s no real way to know!

My Joey tree is already bushing out nicely, I’m debating cutting some of these smaller branches to be scions for the frankentrees:

It looks like I may have gotten a cutting from a Bacon seedling to root, this one has been over a month in dirt and looks to be perking up a bit lately:

I had read that the Mexican subspecies roots more easily than the other two types, but so far none of my attempts have succeeded, which have consisted solely of sticking cuttings removed for grafting into water or dirt and covering with a humidity dome until they die (usually a couple weeks). I’m removing the dome from that one to see if it can make it.

The Jade plant I picked up in Gainesville is pushing a strong flush of growth after the heat wave:

I don’t think I’ve added this one yet, but even though I’m skeptical of the hardiness of Bacon, I picked up an allegedly superior Bacon seedling selection (left), grafted on its own seedling rootstock (right), both of which I will allow to grow out:

Looks like my Poncho graft from a few weeks ago (on Bacon seedling rootstock) is starting to push:

And to finish out this update, my first likely fatality since winter…

I accidentally snapped the end of the taproot on this Royal-Wright seedling when planting it out, and it looked droopy for a bit, but then we got that heat wave and it doesn’t look like it’ll recover… but the seed is still down there so maybe it’ll push another shoot!

ramv · July 6, 2021, 11:13pm

I found this interesting avocado article just today — posted elsewhere.

swincher · July 6, 2021, 11:21pm

Thank you for sharing! I’ve been to Fairchild (and also the nearby Fruit & Spice Park), and they do have impressive collections of West Indies and Guatemalan avocados, but the Mexican type is sadly poorly represented even though it’s likely the original wild type that the others were bred from, and has impressive genetic diversity in the Mexican highlands. A genetic diversity that is quickly disappearing as people replace old trees with Guatemalan types.

swincher · July 14, 2021, 9:17pm

Just got a new book and even after just skimming the table of contents and introduction I can tell this is going to be a good one:

I like this way of displaying the growth pattern of the avocado:

Here’s the description of the book copied from the link above:

This new manual for avocado growers and pest control professionals is the latest in UC’s highly regarded series of Integrated Pest Management Manuals. Drawing on the expertise of UC faculty, UC Cooperative Extension specialists, farm advisors, and pest control advisors, this beautifully illustrated guide gives you the latest research and advice on Pest Management for avocados.

Using this guide you’ll learn how to:

• Prevent and diagnose causes of damage
• Identify pests and key natural enemies
• Establish an IPM program for your grove
• Use biological control and other non-chemical methods
• Manage problems related to irrigation, nutrition, and the growing environment
• Determine when direct control actions are warranted

Illustrated with 386 color photographs and 64 line drawings and charts that will help you identify and manage over 100 important pests and disorders.

swincher · July 17, 2021, 4:58am

Marta wasn’t kidding about the brilliant red color of fresh Royal-Wright growth. It’s the lower-left graft, lower-right is Duke, upper two are both Aravaipa:

I also just grafted a new scion of Brazos Belle onto a Bacon seedling. I’m experimenting with using the growing tips rather than a more solid lower piece of branch, and leaving the smallest leaves intact:

swincher · July 20, 2021, 3:34am

It looks like some of these seeds may have been infected with something. I had thrown out one of them when they came because it was blackened, and I gave the rest a hydrogen peroxide bath before sowing, but two more showed signs of rot so I pulled them and split the seeds to check on the embryos:

Definitely doesn’t look healthy! I’ve never had this issue with germination before so hopefully I haven’t contaminated my greenhouse with something nasty! The other six are fine so far

swincher · August 1, 2021, 5:10pm

I’ve had a busy couple of weeks with the avocados, and I think I’m almost done planting trees in the ground for this year (maybe one more to go), so I thought it would be a good time for a post just listing the first batch of seedlings fated to spend their first full winter in the ground, with a little info about each one.

No. 23 (seedling of Mexicola)

germinated: December 20, 2020
planted out: January 22, 2021

I have often posted about this little tree, which was originally planted out because it was suffering from root rot indoors, intended to be euthanasia. However, despite melting in a hard frost, it sprouted back from the roots in the spring. It melted again during the heat wave, but was revived by a deep watering. It still isn’t the healthiest looking tree of the bunch, but after all it’s been through I’m rooting for it to make it. It is planted just above a drystone rock wall on the highest level of the back yard, so it should have excellent drainage in the rainy winter.

No. 25 (seedling of Mexicola Grande)

germinated: December 31, 2020
planted out: early March 2021

This is the second oldest seedling in the yard, and it’s still clinging to a couple of its oldest leaves that prove it withstood a few freezing nights in March ranging from ~26°F to ~31°F. Some of the later seedlings of Royal-Wright have overtaken No. 25 in size, but not by a whole lot. This tree is planted on the terraced mid-level of my back yard, with good sun exposure year-round, but shade starting in the late afternoon. Like most of my avocado seedlings in the ground, it shrugged off the heat wave in late June.

No. 51 (seedling of Mexicola Grande)

germinated: January 13, 2021
planted out: early March 2021

Much like its elder sibling, this seedling withstood some proper freezing temperatures in March, though it has shed those frost-bitten leaves already. Earwigs have been tormenting it by nibbling new leaves, but they don’t seem to be causing more than cosmetic damage. This tree is closest to my house of all the seedlings in the ground, and gets quite a bit of afternoon reflected heat from a concrete wall a foot and a half away on the east side. Amazingly despite that it also did not seem to mind the heat wave.

No. 53 (seedling of Mexicola)

germinated: January 17, 2021
planted out: end of July 2021

This tree spent more time outside in its pot than almost any of the others, and despite experiencing multiple mid-to-upper 20s nights, it never showed any sign of damage. It had smaller, thicker, darker leaves from a young age than most of the other seedlings. Unfortunately, when I planted this out yesterday, I damaged its roots pretty noticeably. I topped it in the hope that will help it handle the shock of the root damage, and grafted that top onto one of my greenhouse trees just in case I killed it. When preparing the scion, I noticed the leaves have a stronger aroma than many of the seedlings, and there is some other scent mixing with the usual drymifolia scent of anise. Will be very sad if this one was killed by my clumsiness!

No. 84 (seedling of Royal-Wright)

germinated: March 13, 2021
planted out: mid-June 2021

This is the undoubted champion when it comes to vigorous growth, having easily overtaken all the older seedlings in height, trunk girth, number of leaves, and basically any metric one could think of. Unlike most avocados, which seem to grow in bursts, this one seems to just continually push new growth. I’ll be curious to see when/if it slows in the fall. Hopefully it goes dormant in time for winter! This is planted on the lowest level of the back yard, so there is a non-porous layer of hard glacial clay about 2-3 feet below the surface, which could cause root rot issues during periods of heavy rainfall.

No. 91 (seedling of Royal-Wright)

germinated: March 20, 2021
planted out: mid-June 2021
grafted with Royal-Wright: late July 2021

This was probably the second most vigorous tree in the ground, though it’s hard to tell now that I’ve cut its top off to graft its mother onto it. For most of the first-year trees in the ground, I’ve decided to see how they do un-grafted, but I always have the urge to experiment, so I thought I’d try grafting Royal-Wright onto one of them, and No. 91 pulled the short straw. It is planted along the top of the same rock wall as No. 23, though in an area that may get little or no direct sun during the lowest-sun-angle days in mid-winter, so the ground may end up freezing here during a cold snap.

No. 96 (seedling of Purple Nebula)

germinated: April 2, 2021
planted out: mid-June 2021

One of the most vigorous seedlings of this exciting drymifolia variety that I obtained from someone on the tropical fruit forum. Planted next to the greenhouse, so also on the lowest level of the yard with potential deep drainage issues during extra wet periods. It is also near the northeast corner of the greenhouse, so receives morning to midday sun, but is shaded for the afternoon and evening.

No. 99 (seedling of Royal-Wright)

germinated: March 16, 2021
planted out: mid-June 2021

This is one of the less vigorous Royal-Wright phenotypes, which typically seem to have redder stems and new growth that turns to softer looking leaves that are a paler shade of green as the leaves mature. However, because Royal-Wright itself has such stunning red leaves, I am curious to see whether the red shade correlates with cold-hardiness. This was planted at the corner of the garden bed on the mid-level of the back yard, with very good drainage and excellent sun exposure.

No. 100 (seedling of Purple Nebula)

germinated: April 4, 2021
planted out: mid-July 2021

I may have accidentally over-fertilized this one because it had pale leaves when I planted it out, but now the lower leaves are showing some signs of fertilizer burn. I’ve watered it deeply a few times hoping to flush it down and looks like the new growth is coming in vigorously. It is planted in the middle of my front lawn, with good morning sun, midday shade, and then late afternoon sun in summer (but likely to be shaded by my house in winter). Soil is deep glacial sand (with some clay content) in the front yard, so drainage shouldn’t be much of an issue.

No. 107 (seedling of Purple Nebula)

germinated: May 22, 2021
planted out: mid-July 2021

I’ll close out today’s post with this, the youngest seedling currently in the ground, which also has the palest leaves of any of my current in-ground trees. I have tried fertilizing it, but so far no sign of improvement. It is planted at the highest point of my yard, next to the front fence by the sidewalk. The soil here is very sandy, and it’s possible the pH is different from most of the rest of the yard, so if it doesn’t improve from mild fertilizing I’ll have to investigate other causes of the paleness. It gets good late afternoon sun, and once it grows above the fence (~4 feet) it will also have good morning sun, but it’s in deep shade of a large fir tree for most of the late morning to early afternoon.

swincher · August 6, 2021, 10:49pm

Just came across an interesting study that did genetic analysis of a few dozen avocado cultivars to determine whether their reported subspecies lineages were accurate. There are a couple surprises!

Here’s a table summarizing their findings:

And they also discovered that the Mexican race (var. drymifolia) is actually two distinct populations: one in north-central Mexico at higher elevation, and one in south-central Mexico at lower elevation, and they broke down the lineage of the cultivars based on that distinction as well:

One interesting finding was that Bacon is not Mexican or a Mexican-Guatemalan hybrid, but rather appears to be a pure Guatemalan avocado. This is surprising in part because it’s a fairly frost tolerant cultivar, a trait usually attributed to Mexican genes.

swincher · August 11, 2021, 5:31am

Decided to rename the thread to be a little more descriptive, sorry if that confused anyone!

In preparation for our second heat wave of the summer, I just finished moving all the potted avocado trees (other than the ones in 12+ gal pots that are too heavy to bother with) into a corner of yard that just gets some midmorning sun but shade most of the afternoon. Gave them a bit of a drenching, too:

In other news all but one of the remaining Mexicola seeds have germinated in the last couple days. Here are a couple of the wee babies poking their heads out of their seeds for the first time:

I’ve also decided that now that I have two small grafted versions of my Poncho tree as backups, I’d try planting it in the ground:

That’s on a Lula seedling rootstock, but it’s grafted pretty low, so I’m planning to mound mulch up over the graft before winter. I can also fashion a cold frame for that raised bed if needed in a pinch, I guess. I also added a scion of Aravaipa to the Poncho tree, though for whatever reason I’ve had only failures with all my attempts to graft onto Poncho so far:

disc4tw · August 12, 2021, 1:27am

would it make sense to focus on the high elevation cultivars for improving cold hardiness based on these findings?

swincher · August 12, 2021, 2:07am

I’m not sure this study had a high enough level of confidence in that particular distinction to use it to eliminate the ones they identify as low-elevation. The fact that Duke-6 and Duke-7 are identified as being almost 100% from separate populations even though they both came out of the same UC rootstock breeding program as sibling seedlings of Duke is a bit of a warning that the distinction might be overstated. Though I guess if Duke is 50/50 low/high elevation then its seedlings could potentially be almost 100% either one…

That being said, visiting the northern Mexico highlands in search of criollos is absolutely on my list of vacations I want to do!