Names: Avocado, Alligator Pear (English); Aguacate,
Origin: The avocado
probably originated in southern Mexico but was cultivated from the Rio
Grande to central Peru before the arrival of Europeans.
Species: 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.
Related species: Coyo
(Persea schiedeana Nees), Anay (Beilschmiedia
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.
Growth Habit: 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.
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.
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.
Fruit: 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
Location: 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.
Soil: 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.
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 accumulation.
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.
Frost Protection: 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.
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
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.
Harvest: 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 consumption.
and seed extracts have been used for a variety of medical application,
including treatment of diarrhea and dysentery and as an antibiotic.
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
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. Season April.
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.
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
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.
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 July.
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 November.
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. Season August.
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 August.
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
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 23° F.
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
Wurtz (syn. Littlecado)
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. Season July.
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.