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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
anay Kosterm)
Adaptation
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.
DESCRIPTION
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.
Foliage: 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.
Flowers: 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.
Fruits: 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 cholesterol.
CULTURE
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 20feet. 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.
Irrigation: 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 9inches 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.
Fertilization: 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.
Pruning: 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.
Propagation: 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 4inch 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 - 4inches 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°. for up to
six weeks. Mexican types discolor quickly and require immediate
consumption.
Miscellaneous: Leaf and
seed extracts have been used for a variety of medical application,
including treatment of diarrhea and dysentery and as an antibiotic.
CULTIVARS
Anaheim
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.
Bacon
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.
Creamhart
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.
Duke
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
Fuerte
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.
Ganter
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.
Gwen
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.
Hass
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.
Jim
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.
Lula
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.
Lyon
Origin R. Lyon, Hollywood, 1908. Central American. Tree columnar,
slow growing, difficult to propagate, often scion incompatible.
Fruit commonly over 24oz., dark glossy green, rough, pyriform, oil
21%. High quality. Tender, to 30°F. Season April.
Mexicola
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.
Nabal
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.
Pinkerton
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.
Queen
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.
Puebla
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.
Reed
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.
Rincon
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.
Ryan
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.
Spinks
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 23°F.
Whitsell
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. 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.
Zutano
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.
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AVAILABLE FROM:
Alan’s Tropical Fruit Trees
Largo, FL
J.D. Andersen Nursery
Fallbrook, CA
Atkins Nursery, Inc.
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Exotica Nursery Inc.
Vista, CA
Green Mart
Orange, CA
Jene’s Tropicals
St Petersburg, FL
Laguna Hills Nursery
El Toro, CA
Northwoods Wholesale Nursery
Mollala, OR
Oregon Exotics
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Pacific Tree Farms
Chula Vista, CA
Papaya Tree Nursery
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Tropical Oasis Farms
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Montoso Gardens
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Just Fruits and Exotics
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