A member of the Lauraceae, Cinnamon and Bay Laurel, family, the Persea genus contains about
150 species, of which Avocado is the most prominent. 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 in cold and salt tolerance.
Over 400 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.
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 trees fall into two flowering types called A and B, depending on the cultivar.
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 the distance between the
trees and the cultivars used.
Years before fruiting: Grafted rootstock 3-4, grown from seed 8-20.
Fruit: Egg-shaped, pear-shaped, or spherical. The yellow-green to
purple-black skin can be smooth or pebbly, and range from thin to thick. The 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. The weight of the fruit ranges between 3-40 ounces depending on the
Months for fruit to ripen: 6-18 depending on cultivar. Avocados
attain maturity on the tree but can only ripen after reaching maturity and 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 the avocado fruit 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, remaining on the tree for 2-3 years.
Some leaf drop when flowering is normal and may continue into warmer weather. Mexican cultivars have
an anise aroma and can be used in cooking. 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 the 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: This tree has a 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.
'Hass' - Hardy to 33°F, performs poorly in temperatures above
85°F, tree grows 15-20' tall, medium sized fruit, small to medium seed, pebbly thick skin, the
standard grocery store avocado outside Florida, excellent flavor.
'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: The flowers attract bees. The fruit attract mammals.
Toxic / Danger: All parts are mildly poisonous to animals. Unripe fruit
are mildly poisonous. The leaves of Mexican varieties and the ripe fruit of all varieties are not dangerous
to humans except in the case of rare allergies.
Persea americana: Avocado 'Wilma' is prolific and produces very
Persea americana: Avocado 'Wilma' on 'Lula' rootstock. The tree is
four years old and has grown 15' tall. Tree photo by Ken Stockton.
Cultivation and Uses
USDA hardiness zones: 8b-11 for a few cultivars, 9b-11 otherwise.
Chill hours: None.
Heat tolerant: A few cultivars, listed above, tolerate temperatures
Sun: Provide all day part shade in the first three years. Allow full
sun only when the tree is over 8' tall and in the ground three years. In its native habitat, this tree begins
as an understory plant.
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
The 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.
The pH tolerance varies by rootstock.
Fertilize: Use organic compost, worm castings, or fish poop. 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
because their decomposition provides the best nutrients. Use leaves, pine needles or shredded bark when
avocado leaves are not available.
Planting: Avocados are successor plants. That is, they grow in
forests where other plants are already growing. The best location is one where another tree, such as a fig,
has successfully grown and been chopped down, or is next to large trees whose roots have colonized the
planting area, and is partly shaded most of the day, especially in the afternoon. The rootlets of the
previous tree(s) provide organic material, have aerated the soil, and have supported an extensive
mycorrhizal fungi network that the avocado tree needs for nourishment.
Time of Year to Plant: Transplant the sapling from a pot into the
ground in mid to late fall (in regions without freezes), or mid to late winter, avoiding both freezing
temperatures and summer heat, never when temperatures are high. The plant needs time to grow enough roots
before summer's heat so that it can supply sufficient water to the leaves.
Avocado leaves need to transpire large amounts of water in high temperatures to stay healthy.
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
, 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 and protect from wind. 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 the 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.
Most avocados found in supermarkets, such as Hass, can only survive a 33-80°F temperature
range and do poorly in hot, dry climates.
A tree grown from seed will not be true to its parents. If it is not grafted, it will take 8-20 years
Avocados do best when planted in soil where other fruit trees have successfully grown for five years
or more. They must be "babied" for the first three years.
Do you have additional information or a different
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