By Gary Gragg


Home-growing the fruit keeps a supply nearby

By Gary Gragg

Bay Area News Group correspondent

Posted: 01/29/2010 02:00:00 PM PST

HOLY Guacamole! That's what I say every time I walk into the produce aisle and see how much a single avocado costs — sometimes as much as $2 each.

But I'm addicted. I could eat three or four a day. That could be a nearly $3,000 a year habit. What to do? Figure out how to grow the darned things myself.

Most people are introduced to avocados in the form of guacamole, often at a Super Bowl party.

Peak avocado season hits right around Super Bowl season. This year, it is expected that 50 million pounds of avocados will be consumed during the Feb. 7 game. That's enough to cover the entire field in guacamole 5 feet deep.

The avocado is a broad-leaved evergreen tree native from Mexico to South America and into the Caribbean. Under ideal conditions, avocado trees can reach 80 feet tall. And it is not uncommon to see trees that are 50 feet tall thriving on benign neglect in the older neighborhoods ringing the San Francisco Bay.

The fruit has been highly regarded in Central and South America for more than 2,500 years — seeds have been found alongside buried mummies in Peru dating back to the 8th century B.C. Comparatively speaking, the avocado is a relatively new introduction to California, having been commercially cultivated here for only about 100 years.

The single seed is usually oblong, but it is sometimes nearly round. The avocado is green or black skinned, and it can be as small as a walnut or as large as a cantaloupe.

Why the enormous range of fruit types? Genetic variability. Each seed produced by an avocado tree has its own unique genetic code and thereby has the ability to vary from its parents, or parent — avocados are self-fertile.

Like most plants man finds useful, avocados exhibiting desirable traits have been isolated and replicated via asexual reproduction for hundreds, if not thousands, of years. This is accomplished by grafting the desired variety onto a seedling rootstock or even onto a mature tree.

This process has given rise to more than 500 named varieties, one of which has dominated: the Hass.

Finding Hass

In 1926, a humble postman earning 25 cents an hour hit the genetic variability jackpot when he purchased an avocado seed from a local nurseryman. Rudolph Hass from La Habra Heights planted his seed, intending to grow a rootstalk upon which he would graft an existing common cultivar.

His seedling grew vigorously, but he failed at least twice in trying to establish a new graft. Hass considered cutting down the tree, but his children loudly protested, liking the taste of the bumpy, odd fruit the tree produced.

In 1935, Hass obtained the very first U.S. patent on a tree and gave his cultivar the family name. He contracted with a local nurseryman to grow and distribute the trees in a deal whereby Hass would collect 25 percent of the net proceeds from sales.

Unfortunately for Hass, commercial growers simply bought a single plant and used it to graft entire orchards.

Hass only made $5,000 from his discovery, yet the Hass cultivar has become the world's most dominant commercial avocado variety, currently accounting for more than a billion dollars in annual sales in the U.S. market alone.

California dominates the U.S. avocado market, producing nearly 95 percent of the nation's crop. Commercial California groves stretch from San Luis Obispo to San Diego County, although limited commercial growing occurs as far north as Monterey County.

As a result of the North American Free Trade Agreement, avocados from as far away as Mexico, Peru and Chile have begun to enter the U.S. market.

To me, this is absurd. Why should a fruit be shipped from the other side of the world to your local grocery, at an enormous environmental toll, when you can grow it yourself just outside your door?

Grow you own

Cultivar selection is of paramount importance. There are three types of avocados: Mexican, Guatemalan and West Indian.

Generally, Mexican varieties are hardy into temperatures in the low 20s and Guatemalan to the mid 20s, but East Indian get fussy in the low 30s, relegating them to semitropical Florida, Hawaii and the most frost-free locations of Southern California.

In Northern California, try using the most cold-hardy and toughest Mexican cultivars, such as California's first commercial type, Fuerte, the low-fat content Bacon, the early ripening Zutano, or the hardiest of all, Mexicola Grande, which has a smooth, dark purple skin and buttery flesh.

And if you are a bit more adventurous, risk tolerant, have a particularly frost-free location or all of the above, try one or more of the Guatemalan varieties, such as the nearly ever-bearing Hass, the Hass-like Gwen, the easy peeling Pinkerton or the summer ripening cannon ball-sized Reed.

Most exciting of all is a new Mexican type variety named "Sir-Prize" that was derived from a Hass seedling. It produces a fruit very similar to Hass except larger. But it is much more cold-hardy than its tender grandparent.

If you would like more than one variety but are short on space, simply plant two or three in the same hole and allow them to grow into a multi-trunk, multi-variety single tree.

And if you only have room for a large pot on a deck or balcony, choose the dwarf Littlecado, also known as "Wurtz."

Site selection

In Northern California, the ideal avocado-growing location is just beyond the fog belt, on a south-facing slope at least 200 feet above the valley floor, 250 feet to 1,200 feet above sea level.

Being just beyond the fog belt allows for increased heat without being so far inland that the trees become scorched and stressed from the hot summer sun. Planting on slopes allows for excellent drainage to prevent root rot and increased frost protection because dense cold air sinks and accumulates on valley floors, bypassing plantings on higher slopes.

If the slope faces south, the trees will enjoy much more winter sun and warmth because of the low angle of the winter sun. That said, avocados also can be successfully grown outside these "ideal" site conditions.

Tree planting

Avocado plants are commonly available in 5- and 15-gallon container sizes. Select a tree that appears vigorous and healthy. Dig a hole twice the width and slightly deeper than the container and plant the tree an inch or two higher than the prevailing grade because the plant will surely settle over time.

Backfill the hole with equal parts native soil and well-aged compost, mixed thoroughly. Use the excess soil dug from the hole to create a water basin around the plant to assist in irrigation. Tamp the soil and water deeply to relieve any air pockets.

To prevent damage to the young plant from frost, wind, sun and animals, surround the tree with a mesh cage held in place by rebar stakes. Drape burlap or shade cloth over the cage for the first few years or until it outgrows the apparatus. If gophers are active nearby, cage the root ball using half-inch aviary wire netting, taking care to wrap the entire core root ball to the point of the exposed trunk.

During the first several years, water deeply, thoroughly and frequently to encourage maximum root and top growth. The tree will become more drought tolerant with age, but remember that a well-watered tree will be healthier and bear more fruit than a similar drought-stressed-tree. Always supply ample water during fruit set.

Fertile fruit

A common misconception about avocados is that they are not self-fruitful. This is false, but the flowering habit of avocados is unique in that the flowers are perfect, having both male and female organs, but the parts do not function together.

Avocados are divided between type A and type B flowering cycles. Flowers of type A varieties open in the morning as receptive females, then close in the afternoon until the following afternoon when they reopen for pollen shed.

On the other hand, flowers of type B avocados open in the afternoon as receptive females, close overnight and reopen the following morning to shed pollen.

In other words, the girls and the boys on the same tree just aren't getting together at the right moment. To ensure maximum fruit set, plant type A and B avocado varieties in close, or even overlapping, proximity to each other.

And because bees are the prime pollinators of avocados, anything to increase their numbers in and around avocado trees during their flowering period likely will increase fruit set. Try bee-loving plants such as rosemary. Or establish a hive near your trees.

And remember that avocado trees are beautiful, shade-producing evergreens. They should be used as ornamental plantings and not just relegated to the orchard.They incorporate especially well into subtropical, Mediterranean and Spanish themed gardens. Be aware, though, that they can grow large and have significant leaf drop.

But the benefits of fresh guacamole far outweigh any potential downsides to having this wonderful tree around.

Gary Gragg, a Bay Area native who long has nurtured a passion for plants, owns Golden Gate Palms and Exotics in Point Richmond. Contact him at or through

Avocado info

Here is a list of varieties that are proven winners in the Bay Area. The name of the variety is followed by its cultivar, flower type and hardiness.

    Mexicola Grande, Mexican, A, 20 degrees

    Bacon, Mexican, B, 21 degrees

    Zutano, Mexican, B, 22 degrees

    Fuerte, Mexican, B, 23 degrees

    Sir-Prize, Mexican, B, 24 degrees

    Hass, Guatemalan, A, 26 degrees

    Pinkerton, Guatemalan, A, 27 degrees

    Reed, Guatemalan, A, 27 degrees

    Gwen, Guatemalan, A, 27 degrees


By Gary Gragg

Contra Costa Times correspondent

Posted: 11/12/2009 10:00:00 AM PST

Updated: 11/13/2009 11:04:29 AM PST

The autumn leaves on a black oak are semi-translucent. This tree grows in Lafayette. (Gary Gragg )

YOU'RE STOPPED at a red light, lost in the music coming from your car stereo, when suddenly you hear a large thud on your roof.

Clunk! And then another. You're under attack! Infuriated, you survey the scene for the delinquent prankster lobbing rocks onto your car, but it is nowhere to be seen. Then you catch sight of the ammo. It's not rocks — it acorns, falling from the massive 300-year-old oak you've stopped beneath.

Welcome to acorn season.

Acorns seem to be everywhere this time of year, littering driveways, filling rain gutters and smothering smaller ornamental plants. But just a few centuries ago, this acorn crop was highly anticipated and celebrated much the way we herald the grape harvests of today.

The acorn crop was essential to the people harvesting it. Acorns were collected by the thousands, and the inner fruit of the seed was ground down into flour, usually in the small depressions of nearby boulders.

But that was then and this is now. Now they simply litter the landscape and ultimately become part of the nutrient cycle unless they are lucky enough to be carried off by a squirrel or a jay, dropped in a favorable location and, with a lot of luck, grow into majestic tree.

There are more than 300 species of oak worldwide and more than 60 in North America alone. At least seven "true species" and several more natural hybrids call the East Bay home. Most of us are familiar with the two most common oaks growing here: the valley oak and coast live oak.

The ubiquitous valley oak, Quercus lobata, is the largest and tallest of all the North American oaks and it dominates the valley floors, growing up to 100 feet tall and living as long as 600 years.

It has lobed, deciduous foliage, grows fast and is very attractive. As it ages, the bark can become deeply fissured, resembling the rough skin of an alligator. In the landscape, valley oak makes for a fantastic shade tree that can be used in residential situations or as a boulevard street tree. Nothing says California more than this tree.

Coastal oak

The coast live oak, Quercus agrifolia, is easily identifiable in that it is evergreen and not generally as large as the valley oak. It has smoother bark and smaller, evergreen foliage armed with small prickly thorns.

This is a fantastic tree to use as a large hedge for privacy, a windbreak, or as a tree to create deep shade throughout the year. It can reach heights of up to 75 feet given three or four centuries. After only 10 years in the ground, given favorable conditions, it can grow to 20 feet tall and 30 feet wide with an 18-inch caliper. Coast live oak grows throughout the region but as it likes terrestrial and atmospheric moisture, the closer you get to the fog belt, the more dominant the tree becomes in the landscape. This is the tree that gave Oakland its name.

Blue oak

On the other end of the spectrum, the hotter and drier the habitat becomes, the more likely the drought-tolerant blue oak will dominate the scene. The blue oak, Quercus douglasii, is the ultimate water conservationist. Its foliage has a bluish, silvery cast to reflect the sun's harsh rays and is stiff, sparse and small with very little surface area, keeping transpiration water loss to a minimum.

The tree grows very slowly and conservatively, relying upon a dense and elaborate root system to develop before it commits to top growth. Trees with 18-inch diameter trunks can be several hundred years old.

It makes for an interesting foliage contrast plant in the garden where a medium to smaller tree is desired. Many fine examples can be found in and around Martinez's Hidden Lakes Park, along the Briones Ridge top, and growing among the sand stone outcrops of Walnut Creek's Castle Rock Park.

Fall color

Black oak, Quercus kellogii, is a medium sized deciduous tree that has the largest and most lustrous green foliage of our local oaks. Because of its large and lush foliage, it almost has the appearance of being tropical.

As an added bonus, once temperatures drop in fall, it turns a gorgeous, bright yellow before going bare for the winter. This golden autumnal display is set against the nearly black trunks, from which the plant earned its common name.

The black oak is also an important lumber crop, producing fine hard wood so durable and dense that at one time car axles were turned from choice sections of trunk. Acorns of the black oak were also a favorite of the native Indian population because mash from these acorns tasted sweeter and had a thicker consistency than other species.

You'll find the black oak locally mixed in with valley and coast live oaks, especially on north and east facing slopes. Look around this time of year; they are easily spotted because they are the only oak to turn bright yellow in fall.

Rarer and harder to find is the interior live oak, or Quercus wislizenii, an evergreen that can take two forms: a medium to large tree reaching 70 feet tall, or a small shrub variety named Quercus wislizenii frutescens that grows in dense thickets reaching only 10-12 feet high.

The height difference is a direct response to habitat. Go to the top of Mount Diablo where it is windy and exposed and you'll find the shorter variety. Farther down the mountain, in more protected locales such as at Juniper Camp, you'll find massive trees reaching for the heavens.

To the untrained eye, the tree can be mistaken for coast live oak. The foliage of interior live oak is more pointed and flatter than its coastal cousin.

Coast live oak also has gray or rusty fuzz on the backside of its foliage whereas interior live oak has no such fuzz. Interior live oak makes for a wonderful drought-tolerant and evergreen landscape shade tree.

Wide ranging oak

Another oak popping up here and there in our area is the Canyon oak, Quercus chrysolepis. The Canyon oak is the most widely distributed oak in California, ranging from Central Baja into Oregon, and from the Mojave Desert into the Sierra and over to the Channel Islands off Santa Barbara.

Around here we can find it happily living in Las Trampas Regional Park and on the slopes of Mount Diablo. Like Coast and Interior oaks, it's evergreen. The main difference is that Canyon oak's leaves are both elliptical and bi-colored — darker and shinier green on top, and dull lime green underneath.

It's also called the maul oak because the wood is so dense and strong that early pioneers used it for wedge mauls to split other, less dense trees such as redwood.

Strange visitor

The rarest oak growing in our region is the desert oak, Quercus palmeri. No one really knows how it got to our area. Quercus palmeri is a shrub oak usually reaching no more than 10-15 feet in height. It's evergreen with nearly round foliage that is wavy and heavily spined on its margins.

Like canyon oak, it's also two-toned with dull green on its upper leaf surface and yellowish below. Its only local home is on a single, windswept hilltop called Brushy Peak Regional Park, just north of Interstate 580 near the Altamont Pass.

The desert oak's normal habitat is along desert margins of Northern Mexico and Southern California. The stands of desert oaks at Brushy Peak are exceedingly rare. The nearest stands outside Brushy Peak are more than 200 miles to the south in the Mojave.

How they became established on that isolated hilltop is anyone's guess, although we're pretty sure it wasn't the squirrels or the jays.

Maybe space aliens?

Gary Gragg is the host of HGTV's "Superscapes" and owner of Golden Gate Palms and Exotics in Point Richmond. Gary is a Bay Area native who has long nurtured a passion for plants. Reach him at or through

Planting oaks

Choose a large, solid acorn that does not have any visual damage to it.

Collect more than you need.

Dump the acorns in a pail of water and discard those that float, keeping the acorns that sink.

Find the spot for your new tree and plant several acorns to increase your chances of a healthy sprout. It is best to plant acorns directly where you want the tree to grow instead of in containers. The taproot makes this plant hardy and drought tolerant, and a tap root will not develop properly in a container.

Plant the seeds on their sides, 12 inches apart and 2 inches deep.

Mulch the entire area 4 inches deep within 3 feet of the seedbed. The mulch will suppress weeds, help retain ground moisture from evaporation and act as a fertilizer as it decomposes and releases nutrients.

To protect your investment, place a 4-inch plastic drain pipe vertically over the seed, secured in place by a vertical piece of half-inch diameter rebar pounded into the ground. Place mesh screening over the top, held in place by tie wire. The pipe will protect the young seedling from being smothered by weeds, eaten by deer, or being run over by man or machine. In three or four years, the seedling will break through the top of your protection tube and you can remove it.

Sudden oak death affects three true oak species -- coast live oak (Quercus agrifolia), California black oak (Q. kelloggii), and shreve oak (Q. parvula var. shrevei) -- as well as tanbark oak (Lithocarpus densiflorus). There is no cure for the disease but there may be in the future. For information on the disease and its control, go to