Avocado (Persea americana)

Persea americana, widely known as the avocado plant, is an evergreen tree (semi-deciduous in cooler climates) that is native to Central America. It is cultivated all over the world for its nutritious fruits. Avocado has become an important plant in many cuisines due to its high nutrient and fat content, creamy texture, and distinct taste.

I. Appearance and Characteristics

The word avocado comes from the Spanish aguacate, which derives from the Nahuatl (Mexican) word āhuacatl , which goes back to the proto-Aztecan *pa:wa. In Molina’s Nahuatl dictionary “auacatl” is given also as the translation for compañón “testicle”, and this has been taken up in popular culture where a frequent claim is that testicle was the word’s original meaning. This is not the case, as the original meaning can be reconstructed as “avocado” – rather the word seems to have been used in Nahuatl as a euphemism for “testicle”.

The modern English name comes from a rendering of the Spanish aguacate as avogato. The earliest known written use in English is attested from 1697 as avogato pear, later avocado pear (due to its shape), a term sometimes corrupted to alligator pear.

Persea americana is a tree that grows to 9–20 m (30–66 ft) with a trunk diameter between 0.3–0.6 m (1–2 ft). The leaves are 8–25 cm (3–10 in) long and alternately arranged.

• Flower

Panicles of flowers with deciduous bracts arise from new growth or the axils of leaves. The tree flowers thousands of blossoms every year. Avocado blossoms sprout from racemes near the leaf axils; they are small and inconspicuous 5–10 mm (3⁄16–3⁄8 in) wide. They have no petals but instead 2 whorls of 3 pale-green or greenish-yellow downy perianth lobes, each blossom has 9 stamens with 2 basal orange nectar glands.

• Fruit

The avocado fruit is a climacteric, single-seeded berry, due to the imperceptible endocarp covering the seed, rather than a drupe. The pear-shaped fruit is usually 7–20 cm (3–8 in) long, weighs between 100 and 1,000 g (3+1⁄2 and 35+1⁄2 oz), and has a large central seed, 5–6.4 cm (2–2+1⁄2 in) long.

The species produces various cultivars with larger, fleshier fruits with a thinner exocarp because of selective breeding by humans.

II. How to Grow and Care

Sunlight

Avocado trees require plenty of sunlight to thrive. They do best in a location that receives full sun for at least 8 hours a day. Adequate sunlight is crucial for healthy growth and fruit production. Avoid overly shady areas, as this can hinder the tree’s development.

Temperature

Avocado trees are tropical to subtropical plants and are not very cold-hardy. They grow best in temperatures between 50-85ºF (10-20ºC). Young trees are particularly sensitive to cold and can be damaged below 32°F (0°C). Mature trees can withstand slightly lower temperatures (down to around 28°F, or -2°C, for short periods) but will suffer damage in prolonged cold spells.

In colder climates, avocados can be grown in containers and moved indoors during winter, or special care must be taken to protect them from frost, such as using frost cloths or heaters. Choosing cold-hardy avocado varieties and planting in sheltered locations can also help improve cold tolerance.

Watering

Avocado trees benefit from infrequent, deep watering. This encourages deeper, stronger root growth. Wait until the soil begins to dry out, then water deeply. During the summer months, the avocado tree will require more frequent watering.

Young trees also require more frequent watering as they become established. Mature trees should receive around 2 inches of water per week.

Soil

The ideal soil for avocado trees is well-draining and fertile, with a slightly acidic to neutral pH (5-7). They are sensitive to alkaline soils. Avoid heavy clay soils as they do not tolerate waterlogged conditions. Amend poor soils with organic matter to improve fertility and drainage.

Fertilizing

Fertilizing an avocado tree starting in the late winter to early spring and feed until the fall, depending on the specific instructions included with your chosen fertilizer. Fertilizers specifically designed for avocado or citrus trees work well.

Pruning

If avocado trees are grown from seed, start pruning when the seedling is only 6 inches tall, snipping off the top pair of the leaves. When it reaches a foot in height, trim it back 6 inches. After this, prune the tree yearly.

Mature trees require occasional pruning. Light pruning can be done any time of year, though heavy pruning should be done in the early spring. Prune thick areas to ensure adequate light and airflow. Cut back any dead wood and trim away V-shaped branches. Don’t take off more than one-third of the length of each branch.

Propagation

Propagating an avocado tree can be a rewarding experience. There are primarily two methods: seed propagation and grafting. Here’s how to do both:

Propagating Avocado from Seed

Extract the Seed:

• Carefully remove the seed from a ripe avocado without cutting it.
• Clean the seed in water to remove any flesh, being careful not to remove the brown skin on the pit.

Prepare the Seed:

• Identify the top (narrower, pointy end) and the bottom (broader, flat end) of the seed.

You can start the seed in water or soil:

• In Water: Stick three or four toothpicks into the seed around its circumference and suspend it, broad end down, over a glass of water, ensuring the bottom 1/3 is submerged.
• In Soil: Plant the seed in a pot with the top 1/3 sticking out of the soil.

Germination:

• Place the pot or glass in a warm, sunny spot.
• If in water, change the water regularly to prevent mold.
• Germination can take anywhere from 2-6 weeks.

Transplanting:

• Once the seedling reaches 6-7 inches tall (15-17 cm), transplant it to a larger pot with soil if it was started in water.

Propagating Avocado by Grafting

Choose a Rootstock and Scion:

• The rootstock is usually a seedling or a young tree, and the scion is a cutting from a mature, fruit-bearing avocado tree.
• Ensure the scion is from a healthy, productive tree.

Grafting Process:

• Common grafting methods include cleft grafting or bud grafting.
• Make clean cuts on both the rootstock and the scion.
• Fit the scion onto the rootstock so that the cambium layers (just beneath the bark) match up.
• Secure the graft with grafting tape or a rubber band.

Aftercare:

• Keep the grafted plant in a sheltered, humid environment until the graft heals and shows new growth.
• Once established, care for it as you would any young avocado tree.

Tips for Successful Propagation

• Patience is key, especially when propagating from seed, as it can take several years for a seed-grown tree to bear fruit, if at all.
• Grafting is preferred for fruit production, as it ensures the new tree will inherit the fruit characteristics of the parent tree.
• Always use clean and sterilized tools when grafting to prevent disease transmission.

How to Grow in Pots

Avocados can be grown in pots outdoors, though it will stifle their growth. (They can also be grown indoors in pots.) This is ideal for small yards or gardens near the northern edge of the avocado’s growing zones, as potted trees can be moved to a protected area when cold weather arrives.

Young trees or dwarf varieties are ideal for growing in pots as these will stay small for some time. When choosing a container, be sure it drains well and has unobstructed drainage holes, ideally a terracotta pot since it’s more breathable.

Overwintering

When grown in the appropriate zones, avocado trees do not require extra care during the winter

unless the area experiences a frost. Protect the tree from a cold front by wrapping it loosely in burlap and adding extra soil at the base of its trunk until the frost has passed.

For trees grown on the northern edges of their growing zones, it is best to keep them in pots so they can be moved to an area protected from cold weather.

Pests and Diseases

Common pests that may bother an avocado tree include mites, caterpillars, borers, lace bugs, and thrips. Diseases include root rot, fruit rot, sun blotch, and cankers. Be alert to the presence of these pests or early signs of disease. Prompt action is the best way to remedy any developing problems before they threaten the health of your avocado tree.

III. Uses and Benefits

• Ornamental uses

Avocado is cultivated for itsedible fruit. This tree typically only grows in hot, dry climates and can be difficult to develop. However, it can be grown as a garden ornamental or as an indoor potted plant, without producing fruit. In outdoor landscapes it considered a successor plant, growing where other plants have already resided.

• Culinary uses

The fruit of horticultural cultivars has a markedly higher fat content than most other fruit, mostly monounsaturated fat, and as such serves as an important staple in the diet of consumers who have limited access to other fatty foods (high-fat meats and fish, dairy products). Having a high smoke point, avocado oil is expensive compared to common salad and cooking oils, and is mostly used for salads or dips.

A ripe avocado yields to gentle pressure when held in the palm of the hand and squeezed. The flesh is prone to enzymatic browning, quickly turning brown after exposure to air. To prevent this, lime or lemon juice can be added to avocados after peeling.

The fruit is not sweet, but distinctly and subtly flavored, with smooth texture. It is used in both savory and sweet dishes, though in many countries not for both. The avocado is common in vegetarian cuisine as a substitute for meats in sandwiches and salads because of its high fat content.

Generally, avocado is served raw, though some cultivars, including the common ‘Hass’, can be cooked for a short time without becoming bitter. The flesh of some avocados may be rendered inedible by heat. Prolonged cooking induces this chemical reaction in all cultivars.

It is used as the base for the Mexican dip known as guacamole, as well as a spread on corn tortillas or toast, served with spices. Avocado is a primary ingredient in avocado soup. Avocado slices are frequently added to hamburgers and tortas and is a key ingredient in California rolls and other makizushi (“maki”, or rolled sushi).

In addition to the fruit, the leaves of Mexican avocados (Persea americana var. drymifolia) are used in some cuisines as a spice, with a flavor somewhat reminiscent of anise. They are sold both dried and fresh, toasted before use, and either crumbled or used whole, commonly in bean dishes.

IV. Harvesting and Storage

On a healthy outdoor avocado tree, you could harvest upwards of 200 avocados per season. For nursery-bought trees, you can expect to see fruit in three to four years. For avocados started from seed, it may take five to 13 years before fruits appear.

When fruits appear, wait until the avocado grows to its mature size. The fruits do not ripen on the tree, so avocados are picked as soon as they are full size. Bring the avocados indoors and let them rest on a counter until ripe.