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
13 (with protection), 15-24
USDA 9 (with ample protection from sun and heat), 10-11

Landscape Use: Edible fruit gardens, large accent tree.

Form & Character: Evergreen tropical to semi tropical tree. Large and spreading.

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.

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

Temperature: Intolerant of frost or temperatures in excess of 115oF. Trunks prone to sunscald.

Light: Full to partial sun, no western exposures of sites with reflected radiation

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 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, paint trunks with using mixture of 50% latex paint and 50% water.

Propagation: Mostly by cutting, seed is difficult

Disease and pests: Avocado 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.

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.

The oil content of avocado fruits is high in monosaturates (similar to olive fruit). Clinical feeding studies in humans have shown that avocado oil can reduce blood cholesterol.  Leaf and seed extracts have been used for a variety of medical application, including treatment of diarrhea and dysentery and as an antibiotic. 

Some popular avocado cultivars include:

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 from Lyon. Guatemala. Tree rather open, moderately tall. Fruit medium, to 12 oz., pyriform, skin thick, pebbled, coppery purple green. Flesh good, oil 19%, seed fairly small. Currently the standard of the industry. To 26 F. Season October.

Origin John Reinecke, San Diego, 1939. Hybrid tree upright habit. Fruit small to medium, to 10 oz., olive green, with long neck, oil 12%. To 26 F. Season June.font>

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. 

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 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 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. 

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. 

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.