Avocado, Alligator Pear (English); Aguacate, Palta (Spanish)
The avocado probably originated in southern Mexico but was cultivated
from the Rio Grande to central Peru before the arrival of Europeans.
Guatemalan (Persea nubigena var. guatamalensis L. Wms.),
Mexican (P. americana var. drymifolia Blake), West Indian
(P. americana Mill. var. americana). Hybrid forms exist
between all three types.
Coyo (Persea schiedeana Nees), Anay (Beilschmiedia anay
Avocados do well in the mild-winter areas of California, Florida and
Hawaii. Some hardier varieties can be grown in the cooler parts of
northern and inland California and along the Gulf Coast. The northern
limits in California is approximately Cape Mendocino and Red Bluff.
Avocados do best some distance from ocean influence but are not adapted
to the desert interior. West Indian varieties thrive in humid, tropical
climates and freeze at or near 32° F. Guatemalan types are native to
cool, high-altitude tropics and are hardy 30 - 26° F. Mexican types are
native to dry subtropical plateaus and thrive in a Mediterranean
climate. They are hardy 24 - 19° F. Avocados need some protection from
high winds which may break the branches. There are dwarf forms of
avocados suitable for growing in containers. Avocados have been grown in
California (Santa Barbara) since 1871.
The avocado is a dense, evergreen tree, shedding many leaves in early
spring. It is fast growing and can with age reach 80 feet, although
usually less, and generally branches to form a broad tree. Some
cultivars are columnar, others selected for nearly prostrate form. One
cultivar makes a good espalier. Growth is in frequent flushes during
warm weather in southern regions with only one long flush per year in
cooler areas. Injury to branches causes a secretion of dulcitol, a
white, powdery sugar, at scars. Roots are coarse and greedy and will
raise pavement with age. Grafted plants normally produce fruit within
one to two years compared to 8 - 20 years for seedlings.
Avocado leaves are alternate, glossy, elliptic and dark green with paler
veins. They normally remain on the tree for 2 to 3 years. The leaves of
West Indian varieties are scentless, while Guatemalan types are rarely
anise-scented and have medicinal use. The leaves of Mexican types have a
pronounced anise scent when crushed. The leaves are high in oils and
slow to compost and may collect in mounds beneath trees.
Avocado flowers appear in January - March before the first seasonal
growth, in terminal panicles of 200 - 300 small yellow-green blooms.
Each panicle will produce only one to three fruits. The flowers are
perfect, but are either receptive to pollen in the morning and shed
pollen the following afternoon (type A), or are receptive to pollen in
the afternoon, and shed pollen the following morning (type B). About 5%
of flowers are defective in form and sterile. Production is best with
cross-pollination between types A and B. The flowers attract bees and
hoverflies and pollination usually good except during cool weather.
Off-season blooms may appear during the year and often set fruit. Some
cultivars bloom and set fruit in alternate years.
West Indian type avocados produce enormous, smooth round, glossy green
fruits that are low in oil and weigh up to 2 pounds. Guatemalan types
produce medium ovoid or pear-shaped, pebbled green fruits that turn
blackish-green when ripe. The fruit of Mexican varieties are small (6 -
10 ounces) with paper-thin skins that turn glossy green or black when
ripe. The flesh of avocados is deep green near the skin, becoming
yellowish nearer the single large, inedible ovoid seed. The flesh is
hard when harvested but softens to a buttery texture. Wind-caused
abrasion can scar the skin, forming cracks which extend into the flesh.
"Cukes" are seedless, pickle-shaped fruits. Off-season fruit should not
be harvested with the main crop, but left on the tree to mature. Seeds
may sprout within an avocado when it is over-mature, causing internal
molds and breakdown. High in monosaturates, the oil content of avocados
is second only to olives among fruits, and sometimes greater. Clinical
feeding studies in humans have shown that avocado oil can reduce blood
Avocados will grow in shade and between buildings, but are productive
only in full sun. The roots are highly competitive and will choke out
nearby plants. The shade under the trees is too dense to garden under,
and the constant litter can be annoying. In cooler areas plant the tree
where it will receive sun during the winter. Give the tree plenty of
room--up to 20 feet. The avocado is not suitable for hedgerow, but two
or three trees can be planted in a single large hole to save garden
space and enhance pollination. At the beach or in windy inland canyons,
provide a windbreak of some sort. Once established the avocado is a
fairly tough tree. Indoor trees need low night temperatures to induce
bloom. Container plants should be moved outdoors with care. Whitewashing
the trunk or branches will prevent sunburn.
Avocado trees like loose, decomposed granite or sandy loam best. They
will not survive in locations with poor drainage. The trees grow well on
hillsides and should never be planted in stream beds. They are tolerant
of acid or alkaline soil. In containers use a planting mix combined with
topsoil. Plastic containers should be avoided. It is also useful to
plant the tub with annual flowers to reduce excess soil moisture and
temperature. Container plants should be leached often to reduce salts.
Avocado trees may not need irrigation during the winter rainy season,
but watch for prolonged mid-winter dry spells. Over irrigation can
induce root which is the most common cause of avocado failure. To test
to see if irrigation is necessary, dig a hole 9 inches deep and test the
soil by squeezing. If it is moist (holds together), do not irrigate; if
it crumbles in the hand, it may be watered. Watch soil moisture
carefully at the end of the irrigating season. Never enter winter with
wet soil. Avocados tolerate some salts, though they will show leaf tip
burn and stunting of leaves. Deep irrigation will leach salt
Commence feeding of young trees after one year of growth, using a
balanced fertilizer, four times yearly. Older trees benefit from feeding
with nitrogenous fertilizer applied in late winter and early summer.
Yellowed leaves (chlorosis) indicate iron deficiency. This can usually
be corrected by a chelated foliar spray of trace elements containing
iron. Mature trees often also show a zinc deficiency.
It is important to choose a cultivar that is hardy in your area. Mexican
types are the best choice for colder regions. Plant above a slope for
air drainage, or near the house for added protection. In youth, protect
with rugs, towels and such spread overhead on a frame. For further
protection heat with light bulbs and wrap the trunk with sponge foam.
These measures also permit tender cultivars to become established in
borderline locations; established trees are much hardier than young
ones. The upper branches can also be top worked with hardy Mexican
types, which will protect a more tender cultivar on lower branches, as
well as serving as a pollinator. Harvest fruit before the frost season
begins. Cold-damaged fruit turns black. Avocados are often in bloom at
the time of frost and the flowers are killed, but the tree tends to
rebloom. This is especially true of Mexican types.
Columnar cultivars require pinching at early age to form a rounded tree.
Others need no training. Current orchard practice avoids staking. The
best results are obtained by fencing the tree with plastic mesh for the
first two to three years. Container and dwarf trees will need constant
staking. The skirts of avocado trees are sometimes trimmed to discourage
rodents, otherwise the trees are usually never pruned. Branches exposed
to sun by defoliation are extraordinarily susceptible to sunburn and
will surely die. Such branches should always be whitewashed. It is
better to avoid any pruning. Most cultivars are ill-adapted to espalier.
They are too vigorous. Avocado fruit is self-thinning.
Desired clonal rootstocks can be be propagated by a method known as the
etiolation technique. The largest seed are planted in gallon cans and
the seedlings are then grafted to a root rot tolerant clonal scion. When
the stem of the graft reaches about 1/4 inch in diameter, the top is cut
off leaving a whorl of buds just above the graft. A 4 inch band of black
tar paper is formed into an extension of the can and filled with
vermiculite and placed in a dark box with high temperature and humidity.
When growth is some 3 - 4 inches above the vermiculite, the plant is
removed into the light where the upper portion quickly assumes a green
color. The tar paper collar is removed, the shoot is severed from the
seed and then placed in flats where the cuttings are rooted in the
conventional manner. Any seed may also be used for rootstock, but
Mexican types make the strongest growth and are the most often used.
Plant cleaned seeds as soon as they are ripe. The seedling plants are
ready to bud the following year. Budding is done in January, when
suitable buds are available. Larger stocks are worked by bark grafts in
the spring. Scions are collected Dec - Jan after the buds are
well-formed. Paint and cover the graft with a moistened plastic bag and
place a vented paper bag over the whole.
Pests and diseases:
Rats and squirrels will strip the fruit. Protect with tin trunk wraps.
Leaf-rolling caterpillars (Tortrix and Amorbia) may
destroy branch terminals. Avocado Brown Mite can be controlled by
powdered sulfur. Six-spotted Mite is very harmful; even a small
population can cause massive leaf shedding. A miticide may be required
if natural predators are absent. Snails can be a problem in California.
Two fungi and one virus cause more
damage than any pests. Dothiorella (Botryosphaeria ribis) canker
infects the trunk, causing dead patches that spreads to maturing fruit,
causing darkened, rancid smelling spots in the flesh. Flesh injury
begins after harvest and is impossible to detect on outside. Mexican
types are immune to trunk cankers but the fruit is not. The disease is
rampant near the coast and has no economical control. Root Rot (Phytophthora
cinnamomi) is a soil-borne fungus that infects many plants,
including avocados. It is a major disease problem in California. Select
disease-free, certified plants and avoid planting where avocados once
grew or where soil drainage is poor. The disease is easily transported
by equipment, tools and shoes from infected soils. Once a tree is
infected (signs include yellowing and dropping leaves), there is little
that can be done other than cut back on water. Sun Blotch is a viral
disease that causes yellowed streaking of young stems, mottling and
crinkling of new leaves and occasional deformation of the fruit. It also
causes rectangular cracking and checking of the trunk, as if sunburned.
It has no insect vector but is spread by use of infected scions,
contaminated tools and roots grafted with adjacent trees. It is
important to use virus-free propagating wood.
The time of harvest depends upon the variety. Commercial standards
requires fruit to reach 8% oil content before harvesting. Mexican types
ripen in 6 - 8 months from bloom while Guatemalan types usually take 12
- 18 months. Fruits may continue enlarging on the tree even after
maturity. Purple cultivars should be permitted to color fully before
harvest. Guatemalan types can be stored firm, at 40 - 50° F. for up to
six weeks. Mexican types discolor quickly and require immediate
Leaf and seed extracts have been used for a variety of medical
application, including treatment of diarrhea and dysentery and as an
Origin Otto Keup, Anaheim, 1910.
Guatemalan. Tree columnar, productive. Fruit very large, to 24 oz.,
elongated glossy green, seed small, oil 15%. Tenderest of cvs. for
coast only. To 32° F. Season July.
Origin James Bacon, Buena Park,
1954. Hybrid. Tree broad, productive. Fruit small to medium, to
12 oz., round-ovoid, smooth green. Flesh only fair, almost
colorless,seed cavity molds rapidly. Hardy for Bay Area, Central
Valley. To 25° F. Season December.
Origin Orton Englehart,
Escondido,1969. Hybrid. Seedling of Reed. Tree open, upright,
branching. Fruit medium, to 14 oz., skin green flesh extraordinarily
pale,buttery, nearly fiberless. Not alternate bearing. To 30° F.
Season April - July.
Origin Bangor (Oroville), 1912.
Tree vigorous, open, resists wind. Fruit small, 12 oz., elongated
pyriform, waxy green, skin paper-thin. Flesh excellent, oil 21%.
Seeds commonly used for rootstocks, resist root rot. Extraordinarily
hardy, recovers quickly from freeze, to 22° F. Season October
Origin Atlixco, Mexico, intro.
Carl Schmidt, 1911. Hybrid. Tree open, spreading, tall. Fruit large
to very large, 16 oz., elongated pyriform, skin dark green with
numerous small raised pale spots, waxy bloom, skin thin. Flesh good,
oil 18%, seed medium. Formerly standard cv. of California industry.
Tends to bear in alternate years, unproductive near coast or in
north. To 26° F. Season December.
Origin Albert Rideout, Whittier,
1905. Mexican. Tree tall, spreading, open. Fruit small, to 8 oz.,
long pyriform, skin paper-thin, pale waxy green. Flesh good, oil
18%. Oldest avocado cv. in California. Quite hardy, for Central
Valley floor and far north. To 23° F. Season October.
Origin Riverside, Robert Whitsell,
1982, patented. Seedling of Hass. Tree dwarf, to 14 ft., low vigor.
Fruit small, to 8 oz., a Hass look alike, elongated green, flesh
good. Most productive of dwarf avocados, best dwarf for outdoor use,
also for containers, greenhouse. Not hardy, to 30° F. Season
February - October.
Origin Rudolph Hass, La Habra
Heights, 1926. Seedling of Lyon. Guatemalan. Tree rather open, not
tall. Fruit medium, to 12 oz., pyriform, skin thick, pebbled,
coppery purple. Flesh good, oil 19%, seed fairly small. Currently
the standard of the industry. To 26° F. Season July.
Origin John Reinecke, San Diego,
1939. Hybrid. Tree upright. Fruit small to medium, to 10 oz., olive
green, with long neck, oil 12%. To 26° F. Season June.
Origin George Cellon, Miami, 1919.
West Indian. Tree dense, broad, prolific. Fruit round, slightly
pyriform, to 20 oz., slightly rough glossy green, oil 12%. Only West
Indian type recommended for California, rather hardy, to 28° F.
Origin R. Lyon, Hollywood, 1908.
Central American. Tree columnar, slow growing, difficult to
propagate, often scion incompatible. Fruit commonly over 24 oz.,
dark glossy green, rough, pyriform, oil 21%. High quality. Tender,
to 30° F. Season April.
Origin Coolidge, Pasadena, 1910.
Mexican. Tree tall and spreading, vigorous. Fruit small, 5 oz.,
round pyriform, skin paper-thin, purplish black, waxy bloom. Flesh
highest quality, seed very large. Hardiest cv. known, seedlings
useful as rootstocks in far north. Recovers rapidly from freeze.
Defoliated at 20° F, trunk killed at 17° F. Season September.
- Mexicola Grande
Seedling selection of Mexicola.
Mexican. Tree tall and spreading similar to Mexicola. Fruit 15% -
25% larger than Mexicola and somewhat rounder in shape with better
seed/flesh ratio. Skin paper-thin, purple-black. High quality flesh
with high oil content. Hardy to about 18° F.
- Murrieta Green
Origin Colima, Mexico, intro. by
Juan Murrieta, 1910. Hybrid. Tree slow growing, easily trained.
Fruit large, to 18 oz., oblate, green, resembling Fuerte. Flesh
exceptional, oil 18%. Only cv. readily adaptable to espalier. For
coast and intermediate. To 27° F. Season September.
Origin Antigua, Guatemala, intro.
by F.W. Popenoe, 1917. Tree dense, columnar. Fruit handsome, large
pyriform, to 17 oz., green, skin resembles Fuerte. Flesh
exceptionally high quality, oil 16%. Young trees require pinching to
force low branching. Tends to bear alternate years. To 27° F. Season
Origin John D. Pinkerton, Saticoy,
1972, patented. Guatemalan. Tree dense, productive. Fruit variable
in size, 7 to 12 oz., skin thick, pebbled, green. To 30° F. Season
Origin Antigua, Guatemala, intro.
by E.E. Knight, 1914. Guatemalan. Tree broad. Fruit exceptionally
large, to 24 oz., elongated, purple, flesh excellent, oil 13%.
Fairly hardy for large cv., worth trying in Bay Area. To 26° F.
Origin Atlixco, Mexico, intro. by
Carl Schmidt, 1911. Mexican. Tree broad, high branching. Fruit
beautiful, medium to large, to 18 oz., ovoid, skin thin, lacquered
maroon purple. Flesh excellent, oil 20%. Least hardy Mexican type,
to 29° F. Season December.
Origin James S. Reed, Carlsbad,
1948. Hybrid. Tree columnar. Fruit large, to 15 oz., round, skin
thick, pebbled, green. Flesh good. To 30° F. Season August.
Origin Carlsbad, Sam Thompson,
1944. Hybrid. Tree small. Fruit small to medium, 10 oz., green,
resembling Fuerte. Flesh good. For coast, Santa Barbara and Ventura.
To 27° F. Season January.
Origin Albert Rideout, Whittier,
1927. Hybrid. Tree low, spreading. Fruit medium, to 14 oz.,
elongated, otherwise resembles Hass, skin thick, pebbled, purple.
Flesh good, oil 25%. For Inland Empire, Bay Area. To 26° F Season
Origin E. Bradbury, Bradbury,
1911. Hybrid. Tree spreading. Fruit medium, to 15 oz., round with
small neck, tangelo shaped. Lacquered, coppery purple, outstanding
flavor, oil 16%. To 27° F. Season April.
- Topa Topa
Origin E.S. Thatcher, Ojai, 1912.
Mexican. Tree columnar, vigorous. Fruit handsome, elongated pyriform,
small to medium, 8 oz., smooth dark purple with white waxy bloom.
Skin paper-thin. Flesh rather poor, oil 15%, seed elongated.
Seedlings commonly used for rootstocks. Hardy, for far north. To
Origin Robert Whitsell,
Riverside,1982, patented. Hybrid. Hass seedling. Tree dwarf, to
12 feet, low vigor. Fruit small, 6 oz., elongated Hass look alike.
Flesh good. Bears in alternate years. For containers and greenhouse
only, not hardy. To 30° F. February to October.
- Wurtz (syn.
Origin Roy Wurtz, Encinitas, 1935.
Hybrid. Tree prostrate, difficult to train, low vigor. Fruit dark
green, medium, to 10 oz. For containers and greenhouse. To 26° F.
Origin R.L. Ruitt, Fallbrook,
1926. Hybrid. Tree columnar. Fruit small to medium, to 10 oz.
elongated smooth green, resembles Fuerte but inferior, has fibers.
Hardy for Bay Area, Central Valley. To 25° F. Season November.
See generally: California Avocado
Society Yearbook, 1915 to present.
Davenport, T.L. Avocado
Flowering, Hort. Reviews 8: 257-289.
Koch, F.D. Avocado Grower's
Handbook, Bonsall Publications, 1983.
Morton, Julia F. Fruits of Warm
Climates. Creative Resources Systems, Inc. 1987. pp. 91-102.
Ortho Books. All About Citrus
and Subtropical Fruits. Chevron Chemical Co. 1985. pp. 16-19