Scientific: Persea 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]
Common: avocado
Family: Lauraceae
Origin: The avocado probably originated in southern Mexico but was cultivated from the Rio Grande to central Peru before the arrival of Europeans.
Pronounciation: Per-SEE-a SPEE-sheez
Hardiness zones
Sunset 13 (with protection), 15-24
USDA 9 (with ample protection from sun and heat), 10-11
Landscape Use: In Phoenix, protected edible fruit gardens, large accent tree. One cultivar even makes a good espalier.
Form & Character: Variably upright, large and spreading depending on cultivar, dense, mesic, tropical. Some cultivars are columnar, others selected for nearly prostrate form. Clean in appearance, but oh, what a litter producer!
Growth Habit: The avocado is a dense, evergreen, soft-wooded perennial tree, shedding many leaves in early spring. It is fast growing and can with age reach 80 feet, although usually much less in Phoenix. Growth is in frequent flushes during warm weather in southern regions with only one long flush per year in cooler areas.
Foliage/Texture: Opposite, thick, glabrous, lanceolate dark green leaves to 6 inches long, sessile, prominent veins, brittle twigs and small branches; medium fine texture.
Flowers: Flowers are in terminal panicles of 200 to 300, and are small and yellow-green. 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, are sterile and abort immediately. 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. Each panicle will produce only one to three fruits. 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 large (weighing up to 2 pounds), smooth round, glossy green fruits that are low in oil content. Guatemalan types produce medium ovoid or pear-shaped, pebbled green fruits that turn blackish-green when ripe. The fruit of Mexican varieties are small (only 6 to 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.
Seasonal Color: None, though the reddish-bronze coloration of new foliage in the spring can be a subtle accent.
Temperature: Intolerant of frost or temperatures in excess of 115oF.
Light: Full to partial sun, no western exposures of sites with reflected radiation. Trunks highly prone to sunscald injury, and are also (like citrus) painted white with a dilute mixture of 50% water and 50% white latex paint to increase albedo.
Soil: Avocado trees grow best in a sandy loam soil. They will not survive in locations with poor drainage due to their sensitivity to root rot pathogens. Zinc deficiency symptoms (interveinal chlorosis) are common in alkaline soil.
Watering: Regular irrigations in desert areas is required.
Pruning: Rarely needs pruning nor should be pruned. The foliar canopy of an avocado tree offers
great protection against trunk sunscald injury and should be allowed to extend to the
ground if possible. If not, as mentioned above paint trunks with using mixture of 50% latex paint
and 50% water.
A special note: Because of its soft-wooded nature, avocado prunage can be difficult to chip and shred.
Propagation: Mostly asexually by cutting, budding or grafting. Seed propagation, though not difficult, is generally not practiced professionally.
Disease and Pests: Avocados are highly prone to pathogenic attack; principally two fungal and one viral species cause more damage than any pest problems. 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 California coast and has control measures that are economically viable. Root rot (Phytophthora cinnamomi) is a soil-borne fungus that easily infects avocado roots in sites
with poor drainage. 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.
Urban herbivory: Squirrels, rats, racoons, birds and all manner of urban critters love to eat the avocado fruits.
Additional comments: The avocado is not suitable for planting in hedgerows, but one can plant two or three trees into a single large hole to save garden space and enhance fertile pollination. For young transplant trees at the beach, in windy inland canyons, or on hilltops one should provide a windbreak of some sort as leaves tatter easily and young branches are soft and weak. Once established however the avocado tree is a fairly tough. Indoor avocado trees need low night temperatures to induce bloom. Container plants should be moved outdoors with care. The roots of avocado trees are highly competitive and in combination with the intense leaf litter will do a nice job of keeping away other vegetation from the base of the tree.
Biomedical notes: The oil content of avocado fruits is rich in oleic acid, a monounsaturated omega-9 fatty acid (also the main component of olive oil). Clinical feeding studies in humans have shown that avocado oil can alter blood cholesterol levels. Leaf and seed extracts have been used for a variety of medical applications including treatment of cancer, blood pressure, vision, depression, inflammation, diarrhea and dysentery, and as an antibiotic.
Some popular avocado cultivars include:
Origin - Otto Keup, Anaheim, California, 1910. Originally from Guatemala. Tree columnar, productive. Fruits very large, to 24 oz., elongated glossy green, seed small, oil 15%. Tenderest of cvs. for coast only. Cold hardy to 32oF, tender. Season July.
Origin - James Bacon, Buena Park, California, 1954. Hybrid tree, broad, productive. Fruits small to medium, to 12 ounces, round-ovoid, smooth green. Flesh only fair, almost colorless,seed cavity molds rapidly. Hardy for Bay Area, Central Valley. Cold hardy to 25oF. Season December.
Origin - Orton Englehart, Escondido, California, 1969. Hybrid seedling of 'Reed'. Tree open, upright, branching. Fruits medium, to 14 oz., skin green flesh extraordinarily pale,buttery, nearly fiberless. Not alternate bearing. Cold hardy to 30oF. Season April - July.
Origin - Bangor, Oroville, California, 1912. Tree vigorous, open, resists wind. Fruits small, 12 ounces, elongated pyriform, waxy green, skin paper-thin. Flesh excellent, oil 21%. Seeds commonly used for rootstocks, resist root rot. Extraordinarily cold hardy to 22oF, recovers quickly from freezing temoperatures. Season October.
Origin - Carl Schmidt, 1911. Originally from Atlixco, Mexico. Hybrid tree open, spreading, tall. Fruits large to very large, 16 ounces, elongated pyriform, skin dark green with numerous small raised pale spots, waxy bloom, skin thin. Flesh good, oil 18%, seed medium. Formerly standard cultivar of California industry. Tends to bear in alternate years, unproductive near coast or in north. Cold hardy to 26oF. Season December.
Origin - Albert Rideout, Whittier, California, 1905. Originally from Mexico. Tree tall, spreading, open. Fruits small, to 8 ounces, 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. Cold hardy to 23oF. Season October.
Origin - Robert Whitsell, Riverside, California, 1982. Patented seedling of 'Hass'. Dwarf tree to only 14 feet, low vigor. Fruits small, to 8 ounces, a 'Hass' look alike, elongated green, flesh good. Most productive of dwarf avocados, best dwarf for outdoor use, also for containers, greenhouse. Cold hardy to 30oF, tender. Season February to October.
Origin - Rudolph Hass, La Habra Heights, 1926. Seedling from Lyon. Guatemala. Tree rather open, moderately tall. Fruits medium, to 12 ounces, pyriform, skin thick, pebbled, coppery purple green. Flesh good, oil 19%, seed fairly small. Currently the standard of the avacado industry. Cold hardy to 26oF. Season October.
Origin - John Reinecke, San Diego, 1939. Hybrid tree with an upright habit. Fruits small to medium, to 10 ounces, olive green, with long neck, oil 12%. Cold hardy to 26oF. Season June.
Origin - George Cellon, Miami, Florida, 1919. Originally from West Indies. Tree dense, broad, prolific. Fruits round, slightly pyriform, to 20 ounces, slightly rough glossy green, oil 12%. Only West Indian type recommended for California, rather cold hardy to 28oF. Season April.
Origin - R. Lyon, Hollywood, California, 1908. Originally from Central America. Tree columnar, slow growing, difficult to propagate, often scion incompatible. Fruits commonly over 24 ounces, dark glossy green, rough, pyriform, oil 21%. High quality. Cold hardy to 30oF, tender. Season April.
Origin - Coolidge, Pasadena, California, 1910. Originally from Mexico. Tree tall and spreading, vigorous. Fruits small, 5 ounces, round pyriform, skin paper-thin, purplish black, waxy bloom. Flesh highest quality, seed very large. Most cold hardy known cultivar, seedlings useful as rootstocks in far north. Recovers rapidly from freeze. Defoliated at 20oF (defoliated), trunk killed at 17oF. Season September.
Origin - Seedling selection from Mexicola, Mexico. Tree tall and spreading similar to 'Mexicola'. Fruits 15% to 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. Cold hardy to about 18oF. can be grown up into central Alabama and southern Georgia. Season September.
Origin - Juan Murrieta, 1910. Originally from Colima, Mexico. Hybrid slow-growing tree, easily trained. Fruits large, to 18 ounces, oblate, green, resembling Fuerte. Flesh exceptional, oil 18%. Only cv. readily adaptable to espalier. For coast and intermediate. Cold hardy to 27oF. Season September.
Origin - F.W. Popenoe, 1917 from Antigua, Guatemala. Tree dense, columnar. Fruits handsome, large pyriform, to 17 ounces, green, skin resembles Fuerte. Flesh exceptionally high quality, oil 16%. Young trees require pinching to force low branching. Tends to bear alternate years. Cold hardy to 27oF. Season July.
Origin - John D. Pinkerton, Saticoy, California 1972, patented. Originally from Guatemala. Tree dense, productive. Fruits variable in size, 7 to 12 ounces, skin thick, pebbled, green. Cold hardy to 30oF. Season November.
Origin - E.E. Knight, 1914. Originally from Antigua, Guatemala. Tree broad. Fruits exceptionally large, to 24 ounces, elongated, purple, flesh excellent, oil 13%. Fairly hardy for being a large cultivar, worth trying in in northern California around San Francisco. Cold hardy to 26oF. Season August.
Origin - Carl Schmidt, 1911. Originally from Atlixco, Mexico. Tree broad, high branching. Fruits beautiful, medium to large, to 18 ounces, ovoid, skin thin, lacquered maroon purple. Flesh excellent, oil 20%. Least hardy Mexican type, cold hardy to 29oF. Season December.
Origin - James S. Reed, Carlsbad, 1948. Hybrid tree, columnar. Fruits large, to 15 ounces, round, skin thick, pebbled, green. Flesh good. Cold hardy to 30oF. Season August.
Origin - Sam Thompson, 1944, Carlsbad, California. Hybrid small tree. Fruits small to medium, 10 ounces, green, resembling 'Fuerte'. Flesh good. For coast, Santa Barbara and Ventura. Cold hardy to 27oF. Season January.
Origin - Albert Rideout, Whittier, 1927. Hybrid tree, low and spreading. Fruits medium, to 14 ounces, elongated, otherwise resembles Hass, skin thick, pebbled, purple. Flesh good, oil 25%. Wide range production in California from warm inland southern California valleys and foothills to the San Francisco Bay area. Heat loving, cold hardy To 26oF Season August.
Origin - E. Bradbury, Bradbury, 1911. Hybrid. Tree spreading. Fruits medium, to 15 ounces, round with small neck, tangelo shaped, lacquered, coppery purple, outstanding flavor, oil 16%. Cold hardy to 27oF. Season April.
Origin - E.S. Thatcher, Ojai, California 1912, originally from Mexico. Tree columnar, vigorous. Fruits handsome, elongated pyriform, small to medium, 8 ounces, 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 growth and production in central and coastal northern California. Cold hardy to 23oF.
Origin - Robert Whitsell, Riverside, California, 1982. Patented hybrid tree from a 'Hass' seedling, dwarf to 12 feet, low vigor. Fruits small, 6 ounces, elongated Hass look alike. Flesh good. Bears in alternate years. For containers and greenhouse only, not hardy. Cold hardy to 30oF. Season February to October.
Origin - Roy Wurtz, Encinitas, California, 1935. Hybrid tree, prostrate, difficult to train, low vigor. Fruits dark green, medium, to 10 ounces. For containers and greenhouse. Cold hardy to 26oF. Season July.
Origin - R.L. Ruitt, Fallbrook, California, 1926. Hybrid tree, columnar. Fruits small to medium, to 10 ounces, elongated smooth green, resembles 'Fuerte', but inferior, has fibers. Hardy as far north as San Francisco Bay Area, Central Valley. Cold hardy to 25oF. Season November.