Cold-Hardy Avocados

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Cold-hardy 'Little Cado' avocado is a dwarf cultivar.
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The Bonny Doon Vineyard's avocado tree is a "tough little sucker" that has survived frosts for more than 30 years.
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Avocado cultivar 'Fuerte' was brought to the United States in about 1912 from the high-elevation cloud forests of Atlixco, Mexico.
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Today, 80 percent of avocados eaten in the United States are from Mexico, and 95 percent are 'Hass.'
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'Ardith' avocado was developed at the University of California, Riverside.
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Ellen Baker is seeking the Holy Grail of cold-hardy avocados.

It’s a typical dayin Northern California — cool, gray, drippy — and water streaks across Ellen Baker’s wool sweater as she leans into thick, glossy foliage to pluck two dangling fruits. They’re avocados (Persea americana).

“We didn’t know how they’d produce here, but turns out they do great,” Baker says, cradling the bumpy, green-black fruits in one hand.

California is avocado country. Ninety-five percent of all avocados grown in the United States are from California, and 65 percent of those come from orchards in San Diego and Ventura counties. Baker’s home and her business, Epicenter Nursery, are in the coastal foothills near Santa Cruz, about two hours south of San Francisco, where the climate is nothing like the dry, blue-sky heat of Southern California. The 30 or so cultivars in her orchard look out of place next to heavily laden apple trees. “People said we were wasting our time planting avocados north of Monterey,” Baker shrugs, “but these avocados really don’t need a lot of heat.”

Avocado Experiments

It’s been 12 years since Baker and her husband, Fred Menge, started their avocado experiment. First, they planted cultivars recommended by the University of California, Irvine’s Avocado Collection that are hardy to their area’s lowest temperature — around 25 degrees Fahrenheit. Some did well, such as ‘Jan Boyce,’ ‘Reed,’ and ‘Carmen.’ Baker flatly didn’t like the fruit of others, such as ‘Mexicola.’ Within a few years, Baker became convinced that she and Menge could find better-tasting avocados that were also better suited to their climate. They began detouring through old neighborhoods, knocking on doors to ask for a taste of backyard avocados on a search for what Baker calls the “Holy Grail.” They found survivors as old as 100 years in abandoned lots, on farms, and occasionally on public streets growing through cracks in the pavement, such as the 30-plus-year-old tree that grows outside the Bonny Doon Vineyard office in downtown Santa Cruz (pictured above). “It’s a tough little sucker,” Baker says, fingering a leaf of the tree’s progeny in her orchard. “It’s what we’re looking for — ones that are really good and will make it through frost. We want a really great avocado; we don’t want a crappy avocado that survives to 20 degrees.”

Old trees in the Bay Area are relics from a time when people believed in a rosier future for northern avocados. A photograph published in a Santa Cruz newspaper in 1935 featured Henry Dakin, who had just won a county fair prize for fruits from his 22-year-old avocado orchard. Captions reported that Dakin grew 125 trees and shipped the slender, green-skinned ‘Fuerte’ cultivar to markets in San Francisco at substantial profit. The newspaper cheerfully predicted that farmers throughout the Bay Area would be sure to follow suit, making the then-infant avocado industry a statewide phenomenon.

Hardy Diversity in the North

In 1935, avocado growers had heard it was possible to grow the trees in northern counties — a tree planted in 1879 stood over the University of California, Berkeley, campus well into the 1960s — but back then growing larger plantings of avocados anywhere in California was experimental. (The bumpy black ‘Hass’ cultivar, today’s supermarket standard, had just been patented that year.)

So, when temperatures plummeted to 16 or 17 degrees in January 1936, abruptly destroying the season’s crop as far south as San Diego, the California Avocado Society (CAS) looked north to see whether the Bay Area yielded any hardier cultivars. They sent Marvin Rounds, a quiet man nicknamed “Mr. Avocado,” to find trees that produced commercial-quality fruit during cold weather. Rounds, too, was searching for the Holy Grail. Mr. Avocado’s enthusiasm for what he found encouraged local growers to dream bigger: He noticed that northern avocados fruited primarily in the fall and winter, a seasonal niche not filled by the south’s spring and summer crops.

“Rounds says the local avocados have the edge on the market because they mature later than the Southern California crop, and hit the market after the southern crop is gone,” explained newspapers under headlines screaming, “AVOCADO INDUSTRY URGED FOR AREA.” Within days, apple grower Joe Reite publicly announced he was ripping out his trees, “making change due to the success Henry Dakin has had with avocados.”

Others followed suit. Copying Dakin, most planted the green-skinned Mexican cultivar ‘Fuerte.’ ‘Fuerte’ and its cousin ‘Puebla’ were brought to the United States in about 1912 from the high-elevation cloud forests of Atlixco, Mexico. There, evening temperatures regularly dip into the low 40s and light freezes are common. Growers appreciated the vigor and frost resistance of ‘Fuerte’ — its name means “strong” in Spanish — and this elongated, shiny, green fruit became the first commercial avocado cultivar in the United States.

How We Got to ‘Hass’

Over the next three decades, the CAS recommended more cultivars. Farmers added ‘Duke,’ a cultivar discovered north of Sacramento that’s hardy to 21 degrees, as well as ‘Nowels,’ ‘Gwen,’ ‘Reed,’ ‘Pinkerton,’ and ‘Noga,’ a now-forgotten Bay Area fruit. The last report from the CAS on northern avocados, warning Southern California to expect competition from “a new avocado producing area,” was issued in 1973 and suggested ‘Bacon,’ ‘Hass,’ ‘Camulo,’ and ‘Zotano.’ Ominously, that same year, the thick-skinned, black ‘Hass’ officially outpaced the thin-skinned, green ‘Fuerte’ as America’s commercial choice. California avocado farms were industrializing, and expectations were changing in ways northern growers couldn’t meet. “The market has changed significantly,” Carl Stucky, a CAS representative, wrote in an email. “In Round’s time, there was little or no fruit in the late fall and winter. Now there’s an oversupply of fruit from Mexico.”

Today, 80 percent of avocados eaten in the United States are from Mexico, and 95 percent are ‘Hass.’ ‘Hass’ and its relatives are not considered cold-hardy. Few people have had success with these cultivars in the northern counties, or, for that matter, with any single cultivar monocrop, even ‘Fuerte.’ “The climate here is just not consistent enough for big acreage,” Baker explains.

Those with the mindset that avocados can’t be grown north of Monterey are right — sort of. The diversity in Baker’s 1-acre plot keeps her flush with mature, quality avocados nearly all year. Word is getting around about her new (old) local cultivars. There’s the ‘Palo de Oro,’ a suspected seedling of ‘Pinkerton’ that’s bigger and creamier than its possible parent. Shiny, jet-black ‘Ibis’ has survived a hard freeze of 19 degrees. ‘Precious’ is a total mystery from Watsonville, abandoned by University of California, Riverside, researchers when their grant ran out. “There are a lot of weird trees there,” Baker says.

At a taste test held in Baker’s orchard in 2015, guests ranked the ‘Bonny Doon’ as one of their favorites. Although she describes the taste as “rich, oily, and nutty,” Baker says its fruits are too small to be the Holy Grail. For that, she’s still looking.


Epicenter Nursery

Avocado Information

University of California, Riverside

Recommended Cultivars

Ellen Baker recommends the following cold-hardy cultivars and sells a limited number of trees via her business, Epicenter Nursery.

• ‘Bonny Doon’
• ‘Jan Boyce’
• ‘Nowels’
• ‘Pinkerton’
• ‘Reed’

Growing Tips

Planting. Plant avocado trees from March to June in full sun. Add 6 inches of coarse, woody mulch.

Fertilizing. Feed 1/2 to 1 pound of nitrogen per tree per year. Also add zinc once a year.

Watering. Soak the soil well two to three times per week and allow to dry between waterings.

Pruning. Trees can be pruned any time of the year, but it’s best done after the winter cold has passed.

Growing from seed. A tree will likely be different from its parent because avocados are most often the result of cross-pollination. Avocados fruit in 5 to 13 years when grown from seed.

Lindsay Gasik is a self-described fruit-hunting geek and horticultural tour guide in Malaysia and Thailand. Follow her atYear of the Durian.

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