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in Tucson, Phoenix,
Arizona and California

Gardening in Tucson, Phoenix, Arizona and California

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Growing Avocados: Persea americana

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Overview
A member of the Lauraceae (Cinnamon and Bay Laurel) family. Avocado plants fall into three major groups: Mexican (v. drymifolia), West Indian (v. americana), and Guatemalan (v. guatemalensis). Some Mexican varieties are the most cold hardy while some West Indian are the most salt tolerant. Guatemalan varieties are intermediate between the two. Over 1000 cultivars and hybrids have been created, with only a few grown commercially. Mexico leads the world in avocado production. In the United States, major production occurs only in California, Florida and Hawaii.

Description
Form: Tree.
Lifespan: 400 years is possible. 30-40 years is typical.
Leaf retention: Evergreen. Some leaves start dropping during flowering, and on into warmer months, and are quickly replaced.
Growth rate: Usually rapid. A few cultivars are slow.
Mature Size: 30-40' high and 25-35' wide is typical. Some can reach 80' in a suitable climate. Dwarf cultivars are available.
Flowers: Yellow-green, small, clustered. While flowers have both male and female parts, avocado cultivars fall into two flowering types called A and B. In the morning, type A are open as females, and type B are open as males. In the afternoon, type A are open as males and type B are open as females. This unusual flowering behavior increases the chance of cross pollination and genetic diversity.
There is an overlap on the same tree between male and female openings, however, especially when previous night temperatures were below 70°F, increasing the chance of bees pollinating flowers within the same tree. Usually no fruit set occurs below 60°F.
Bloom: Late winter or spring. Avocado trees can display "alternate bearing" with a heavy crop in one year followed by a light crop the following year. Some cultivars are more prone to this than others.
Self-fruitful: Yes. Most trees get better at producing fruit with age and residential gardeners do not need a second tree. For commercial growers, two trees, one of flowering type A, the other B, can provide a 20-95% increase in fruit production depending on distance between the trees and cultivar used.
Years before fruiting: Grafted rootstock 3-4, grown from seed 8-20.
Fruit: Egg-shaped, pear-shaped, or spherical. Yellow-green to purple-black skin can be smooth or pebbly, and range from thin to thick. Flesh is light green to yellow. The single seed varies from small to large. Since the tree has an extended flowering period, it will have fruits of varying degrees of maturity. Weight range 3-40 ounces depending on cultivar.
Months for fruit to ripen: 6-18 depending on cultivar. Avocados attain maturity on the tree but can only ripen after reaching maturity and after dropping or being picked off the tree. For many cultivars, the fruit reach full size before they mature, so the only reliable indicator of maturity is when the fruit falls from the tree, making a tarp under the tree worthwhile. One harvesting problem is picking the fruit too soon, before maturity, and then the fruit never ripens.
Storage after harvest: Mature avocados can take 4-5 days to ripen at room temperature. To speed ripening, place in a paper bag with apples or bananas. Once ripe, the only storage is to cut them open, mash the ripe flesh in a bowl, and add lemon juice. This will keep for a day refrigerated or longer frozen.
Leaves: Dark green, glossy, oval, remain on tree for 2-3 years. Some leaf drop when flowering is normal and may continue into warmer weather. Mexican cultivars have an anise aroma. Guatemalan and West Indian leaves, without an anise aroma, are mildly toxic.
Stems: No thorns. The thin green skin on the trunk is prone to sunburn, especially during the first three years. This tree should not be pruned, particularly lower branches, so that its leaves can shield its trunk from direct sun. After three years, the trunk skin gradually hardens into a thicker, bark-like covering.
Roots: Tap root plus shallow feeder roots no deeper than 6-8". Most trees are grafted onto a hardy rootstock.
The 'Lula' rootstock, which originated in Florida, is salt tolerant, does well in alkaline soil, is cold hardy to at least 28°F, and is vigorous and heavy bearing as a tree. This is a preferred rootstock in Texas and Arizona.
The 'Dusa' rootstock is used in California because of its disease resistance, high yield and salt tolerance. It is also known to be hardy in Arizona.
In climates with winter freezes, the graft union should be placed low on the rootstock to make it easy to protect with soil or mulch.
Cultivars of Note:
'Bacon' - Hardy to 25°F, tree grows 20' tall, medium sized fruit, large seed, green skin, low-oil watery flavor, fruit tends to spoil quickly when ripe, average yield.
'Lila' / 'Opal' - Hardy to 18°F, possibly lower, medium sized fruit, green skin, average flavor, average and inconsistent production. Slowly grows about 10" a year, reaching 20-30' tall. Easy to grow in a container for those wanting a small outdoor tree. Will need 50% all day shade protection in the summer for up to 10 years. Sold by Texas nurseries.
'Mexicola' - Hardy to 18°F, very heat tolerant, tree grows to 25' tall and 20' wide, high yield, small fruit with large seed, thin edible skin, very good flavor.
'Stewart' - Hardy to 18°F, tree grows to 30' tall and as wide, low yield, small to medium fruit, medium seed, excellent flavor. This might the best tree for those not wanting an over-supply of avocados when the tree becomes large.
'Wurtz' / 'Little Cado' - Hardy to 25°F, slow growing dwarf tree 8-15' tall, weeping growth habit, small to medium fruit with small seeds, medium-thick green skin, good flavor, consistent moderate yield. Best avocado to grow in a container.
'Zutano' - Hardy to 25°F, tree grows 30-40' tall and wide, grown primarily as a pollenizer for 'Hass' in California. Medium sized, glossy green skin, large seeds, low-oil watery flavor, high yield, poor disease resistance leading to short life span.
Wildlife: Attracts bees. Fruit attracts mammals.
Toxic / Danger: All parts mildly poisonous to animals. Unripe fruit mildly poisonous. Leaves of Mexican varieties and ripe fruit of all varieties are not dangerous to humans except in the case of rare allergies.
Origin: Mexico.

Cultivation and Uses
USDA hardiness zones: 8b-11 for a few cultivars, 9b-11 otherwise.
Sunset climate zones: 16-17, 19, 21, 23-24.
Chill hours: None.
Heat tolerant: A few cultivars, listed above, tolerate temperatures over 80°F.
Sun: Full sun when the tree is over 8' tall and in the ground three years.
Drought tolerant: Yes, after three years in ground.
Water after becoming established: Deep water weekly when fruiting, monthly at other times, especially during drought. Use basin irrigation. Soil should be dry 9" deep before watering. Root rot and other diseases occur in moist soil.
Soil: Very well drained, high in organic content, low salinity, pH tolerance varies by rootstock.
Fertilize: Use organic compost, worm castings, or fish poop. Chemical-based fertilizer use should be avoided so as to keep soil salinity low, a problem with desert soils. In any case, chemical-based fertilizers must not be used the first year in the ground. A composted foliar spray can also be employed.
Mulch: Use up to 1' of mulch. Keep mulch 8" away from trunk in moderate to high rainfall regions. Avocado leaves that have been dropped by the tree make the best mulch. Use leaves, pine needles or shredded bark when avocado leaves are not available.
Planting: Test the proposed location for the tree by digging a hole, filling it with two gallons of water, and checking that the water has drained completely within one hour. If not, place the hole on top of a large mound of soil at least two feet above ground level.
First three years care: During the hottest months of the summer, provide afternoon shade until the plant is over 8' tall. For some cultivars, all day 50% shade cloth may be necessary in the hottest months of the year.
A cloth sheet may need to be draped over the entire tree and down to the ground when nights are below freezing until the plant is 8' tall.
Water the tree every two to three days, unless freezing temperatures are near, using basin irrigation, to establish a strong root system.
During the cold winter months, build a temporary block wall on the north side of the newly planted tree, about 3' away from the tree in the first year, to keep it warm in winter. Use stacked blocks without mortar, about 6' long, 3-4' high and 1' wide. The wall should be white on the north side and dark on the south side facing the tree. As the tree grows, move the wall back to avoid branches and roots. The wall, which will radiate heat during winter nights, may be removed when the tree is more than 8' tall.
Prune: Never prune branches, especially lower branches, except to keep them barely off the ground. The leaves must protect the trunk from direct sun top to bottom. Fruit develops on new growth.
Pruning can be used to dampen alternate bearing. In the fall after a light bearing year, remove 50-75% of new growth that would result in new flower clusters. This will lower fruit set in the following year.
Litter: Fruit if not harvested. Fallen avocado leaves must not be discarded, but used as mulch under the tree, directly on the soil.
Propagation: Cuttings grafted onto rootstock. Seeds are only viable for one month after being removed from their fruit and often do not grow true.
Uses: Ornamental, edible fruit.

Comments
Most avocados found in supermarkets are restricted to climates with a 33-80°F temperature range. Growing from seed without being grafted will produce a tree that will take 8-20 years to fruit.



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Avocado: Persea americana - flowers

Avocado: Persea americana - fruit
Persea americana: Avocado 'Wilma' is prolific and produces very large fruit.

Avocado: Persea americana
Persea americana: Avocado 'Wilma' on 'Lula' rootstock. The tree is four years old and has grown 15' tall. Tree photo by Ken Stockton.


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