I’ve not exactly been hoping for this kind of extreme, but it does give us a chance to observe how some of these experimental avocados fare. That is the question at the crux of this whole exotic avocado project:  Can we expect to successfully grow a Sharwil avocado in our yard, or must we resign ourselves to the thin pleasure of merely planting them over and over again?  Maybe there’s a mathematical equation describing the waning satisfaction in each successive failed attempt, ebbing to a refusal to try another one.  Being the first damaging cold many of these young trees have seen, this is our chance to begin to understand what varieties are going to work for us.

Only spotty data is available on the relative cold hardiness of the avocado varieties we’re trying. Most of it’s from southern Ca., and not very encouraging. Have these varieties even been tried in Santa Cruz County before?  If so, the tablets were lost.  This is a condition endemic to fruit growing. The various western garden references are but a barest of beginnings.  The work of determining the best things to grow is ultimately our own, because everyone’s site is unique and non-uniform, our needs and tastes differ, and lots of good thing have never been tried.

The report offered here won’t apply to everyone’s situation.  You might even laugh at the fact that it’s only a single thermometer (not even digital) upon which I base my data, and so can know almost nothing about the actual thermal landscape of my yard.  These trees, however, are all planted pretty close together (within about a 75’ radius), subject to more or less (as noted in the table below) the same conditions, so there may be some value in comparing and reporting on the damage sustained by each variety. To the extent your place is like our place, this information may be useful.

Damage Rating:

0= no apparent physical damage beyond minor discoloration.

1=almost no damage, only a few tender tips

2=minor damage to tender growth on part of the tree.

3=minor damage to tender growth throughout the tree.

4=clusters of leaves burnt, including larger leaves.

5=mature leaves killed and twig tips burnt back a few inches.

Condition of tree rating (pre-freeze):

Poor=yellowish green color, sparse, blotchy leaves, stalled growth.

Fair=greenish color, thin canopy, blotchy leaves, stalled growth.
Good=green color, full canopy, some signs of growth.

Very good=dark green color, dense canopy, strong growth.

To the extent you’re growing some of the varieties listed in the table above, this first installment of information may help you gauge whether it’s worth trying some others you know not of.  Up here in the avocado outer-reaches, we need to plant the best varieties that have a chance (even if we’re alone in doing so), and we need some luck.   We need to be open to all possibilities, but open as well to the facts when they indicate we’re wasting our time: sometimes a tree just needs to be chopped out.  This job requires a certain degree of cold brutality, tempered with fair-minded leniency.  To not botch too badly this winnowing process we need to tease out some of the various factors influencing a particular trees failure:

Condition of tree is important: Stalled-out, yellow, salt-burned avocado trees are less hardy than healthy ones of the same variety.  High nitrogen levels make avocado leaves more cold resistant.  A tree that looks blue-green, may slide right through a cold event without damage if it’s between growth phases.  With new shoots all over it, the same temperatures may burn it badly, but growth often resumes in what’s survived of those shoots, as soon as things warm up again, leaving you with a bigger, better tree come springtime.

Size really does matter when it comes to avocado cold hardiness.  Large canopies hold more residual heat than tiny shoots, insulating the inner parts of the tree.  So full bushy trees will take more cold than naked straggly ones.  The most vulnerable situation would be the tender shoot from a fresh graft: all soft exposed stem, widely spaced, large succulent leaves.  A tree in this condition could be several degrees less cold tolerant than a full, healthy specimen of the same variety.

Position in the grove can spell doom for a tender variety that would succeed in a more favorable spot.  The temperature varies all over my yard, depending upon whether it’s a high spot on the south side of a fence, for instance, or behind a structure, shaded at sunrise, on the bottom of the yard where the cold air accumulates.  The differing damage levels between the few duplicate trees in my planting indicate, if only weakly, these effects.

Some of the results in the table above are noteworthy, because they’re either extremely good or extremely bad.  Starting with the most stunning failure, the hardest hit tree in the yard was the Ibis.  This tree was just grafted onto the stump of our former Fuerte tree, in late August.  At the lowest point in our avocado line, against a cold air dam in the form of an eight-foot hedge, shaded from the sunrise by the neighbors’ Winnebago, this is unquestionably the worst spot in the grove.  The original Ibis mother tree, a 30-foot tall, 50(?) year old chance seedling was discovered last spring in Corralitos.   It was loaded with tasty, long-necked, Feb-April ripening Mexicola-type fruit weighing up to one pound each.  Growing as it was in a cold part of the county, and displaying Mexican genetic traits, we guessed it would be happier in this bad spot than the Fuerte was.  We guessed it would prove itself to be a great new avocado for colder climates.  We guessed it was our best chance to rapidly screen our view of that blocky white Winnebago.  Maybe we guessed wrong.  All tender green shoots and succulent young leaves, our little Ibis had no canopy to speak of, no hardened-off leaves, and everything burnt back to ¼ inch stems.

You might think privately that only an idiot would be grafting avocados outside in late August.  Isn’t that inviting failure, waving all that tender new growth at the frosts coming only a couple months away?  True, it’s not very smart, but our mid-May graft attempts failed, and the mother tree was being removed.  It’s gone, through the chipper now, so we had one last chance.  The 5/8 inch main stems look fine, the tree will live, but it inspires empathy.  Combination bad position and vulnerable condition will prevent us making any snap judgements on this variety.  We’ll wait and see how it does in the future with a full, hardened-off canopy.

Next worst was the Nabal, despite a much more favorable location.  This small tree has not grown well, and went into winter with old looking leaves and exposed, sunburned stems in the top of the tree.  These mostly turned black, leaving a crown of dead twigs and clusters of full-sized, blackened leaves, while the bottom ¾ of the tree looked only lightly damaged.  It seems this is a slightly frost sensitive cultivar made more vulnerable by the poor condition of the top branches.  It’s encouraging to see clusters of tiny shoots forming throughout the still-surviving upper parts of this and most of the other damaged trees. Could the burn-back act as a growth stimulus?  This is the first time my Nabal has ever shown any enthusiasm.

Next is the Magoon and the Sharwil.  They stand 7’ apart in the grove, and appear similarly afflicted, with blackened clusters of leaves from the recent growth flush.  The damage is evenly distributed, but superficial in that only the freshest growth appears damaged.  The Magoon is notable in that it is actually two trees: our original tree that’s always looked to be near death, and another one we grafted onto a vigorous rootstock and planted a foot away for insurance.  The sallow, chlorotic, original tree is not quite as badly damaged as the healthier newer tree. I think it’s supposed to work the other way around, but the trees don’t seem to know that.  Both the Sharwil and the healthy Magoon were grafted this March.

It needs to be mentioned that some trees just seem to be smarter about cold weather than others.  The Reed, Hellen, Greengold, Bonny Doon, Ettinger, and Lamb to a lesser extent, all managed to restrain themselves from throwing out quantities of early bloom.  In contrast, Hass, Gwen, Carmen-Hass, Pinkerton, Queen, Nowells, and Jan Boyce were all sporting open flower clusters which mostly froze off.  Particularly disastrous was the nearly complete loss of the Carmen Hass trees’ November-set crop.  This tree hardly makes any fruit in the spring, when it’s supposed to, but it starts blooming again in late September.  The honey bees are more desperate in the Fall, as they rummage through the clusters like thrift store shoppers, while the Spring bloom they treat as they do my other avocado flowers, with almost complete indifference.  (Not to brag, but the Carmen Hass held onto more than 50 fruits last November, and the new crop looked just as good until this freeze.) So, except for the late Fall fruit-setting varieties, an early flower thinning can actually be a good thing.  It has been shown to increase fruit set, provided there are enough undamaged flower buds remaining. Still, I prefer the control afforded by a sharp pair of Felcos, and I like it when my avocados bloom late.

The various problem trees mentioned above aroused my maternal instincts.  I was disappointed at their shortcomings, but not surprised, as I suspected their weaknesses.  I’m optimistic about their futures as I feel most of the fault for their failures lies with us, in their shaky condition and/or their very youngness. Time and attention can cure both, and when these trees have more ballast to them, we’ll better be able to judge their relative hardiness.

Some trees in the grove deserve notice not because they failed us, but because they met the challenge unexpectedly well.  The Queen had only minor damage to the tenderest leaves.  Greengold was another one I was worried about, but it came through with only a few tiny tips burnt.  The Ardith, newly grafted in April, grew to four feet, but pretty whippy and thin.  Upper leaves discolored, but only the tiniest tips were singed. Koala, Big Sur Round, Gem and Edranol showed great resistance, boasting only minor reddish brown spotting on otherwise sound leaves.  Carmen Hass and Reed were both carrying big crops of well developed fruit, none of which was damaged.  The tree most unscathed was the Bird Avenue seedling from Willow Glen.  With dense, nutty, Greengold-like flesh, we loved these fruits when Jeffrey Wong of the Santa Clara CRFG shared them, scion-wood, and the story of the tree with us last spring.  Grafted in late April, planted out in July, it has looked pretty sickly and hasn’t grown much since.  Our Bird Avenue tree still has a weak look to it, a bit yellow, stalled-out and vulnerable looking, but the cold seemed to cause no harm.

I feel as un-entitled to celebrate these seeming successes, as I am reluctant to bemoan the tender trees’ failures.  One freeze provides insufficient data to decide anything. A harsher cold snap might kill some things, or require special protective measures, and would certainly provide us with more data.  26° is only a normal season’s low, but it is encouraging, because the trees all seem able to withstand it, and will come through to the spring with blossoms, and fruiting potential intact.

This is the basic test they need to pass.  This minimum hardiness is especially necessary for avocados.  They’re usually too big to protect before they bear fruit, and they carry their fruit through at least one winter, and up here, often two. I feel more secure knowing I needn’t pray for a string of miracle years if I want a chance to eat a Sharwil or a Queen from my own backyard.  Maybe I’m jinxing myself, but these varieties display a durable toughness beneath the tantalizing fantasy.  They can tolerate a normal year’s cold at my house.  That doesn’t mean they will make me lots of fruit.  They may not make any fruit, but hope is alive, and the honeymoon can go on a little longer.